Tag: maintenance (page 1 of 4)

Don’t judge a book by its cover; promote aviation to adults and kids

On Cinco de Mayo I had the pleasure of sharing the “screen” with Julie Clark, Martha King and Pia Bergqvist on Social Flight Live as we each talked about our aviation careers. As we were preparing for the show I found it interesting that we all had very different entrées into aviation. Three of us were children of pilots and one sort of stumbled into aviation by happy coincidence. After the show, [ ] I thought about the old saying, “Don’t judge a book by its cover, you might miss out on an amazing story.” I wonder if we should re-think our approach to inspiring the love of flight, promoting aviation, and protecting airports.

We always love showing off our airplanes to wide-eyed tots, but perhaps it is the adults we should be pursuing.

So pull up a chair and listen to the stories of four women with wildly different backgrounds who became pilots from their teens to their forties.


Julie Clark 18 years

It is hard to think about the small family of female airshow performers without thinking of Julie Clark who has been gracing the skies for decades. What is lesser known is that she had to tell a few white lies to find her way to the blue skies.

Julie started flying lessons while attending University of California Santa Barbara at age 18. Julie was taking lessons on the sly, not telling her Aunt and Uncle who were her guardians, after her parents passed away. The only ones that knew about her clandestine flight lessons were a few of her Alpha Pi sorority sisters. Julie says that she spent her book money on flight lessons in a Cessna 150. I think we can all agree that we are glad she did.


Martha King, 24 years

Martha learned to fly when she was 24 years old. She recalls she was generally not aware of private aviation. Martha’s father was a pilot in the military, but she did not have a passion for it from early on. But her boyfriend John was in love with flying—he used to fly with his father, and with some family friends. After they got married and finally had both some time and some money, John said he wanted to finish getting his pilot’s certificate. Although Martha knew nothing about the process, she said, “I was not going to stay at home while he was out at the airport having fun!” So the couple bought a Cherokee 140 [pictured] and got their certificates together—2 days apart. They did their flight training at Speedway Airport (now gone) and Eagle Creek Airpark in Indianapolis.

It would be hard to imagine aviation education without Martha and John King. So hats off to John for pursuing his pilot’s certificate and to Martha for seizing the opportunity for a lifetime of fun flying.


Pia Bergqvist, 29 years

An 8-year-old Pia Bergqvist was smitten with aviation after a visit to Kallinge AFB in Ronneby, Sweden with her friend whose father was based there. That is when she first laid eyes on the Saab JA-37 Viggen Jet.

Pia’s Uncle was a charter pilot in Sweden, and she flew with him once. She remembered that her Uncle went to the US to get his license. She had never heard of little private planes until moved to Switzerland at 19 yrs. old.  The idea of going to the US seemed too difficult. Further complicating matters she had never even seen a woman pilot. Her desire was there but there was no clear path to get to her goal.

Pia came to the US in August of 1997 [Brentwood, CA]. Pia worked on the USC campus. It was there she befriended a female student who was a flight attendant for Delta, who was working her way through dental school. Pia told her she wanted to be a pilot but that it wasn’t possible, as there weren’t any female pilots. Her new friend told her “yes, there are female pilots and it is possible!” At age 29 Pia went to Santa Monica’s Justice Aviation for her PPL.

Fabulous 40s

 Jolie Lucas, 40 years

I was raised in a General Aviation-savvy family. We drove a modest car, but always had a small plane in the hangar. My Dad was a primary trainer in the Army Air Corps [WWII] at Rankin Field in the Boeing Stearman. We flew, as a family in our Bellanca, then a Mooney to Seattle, WA or Indiana annually.

In 2002 airport day at Jackson/Westover, CA coincided with our Lucas family reunion. While up at the airport my Dad landed in his Mooney, my brother in his Bonanza, and I thought, “What the heck am I waiting for?” I was married, worked full-time as a psychotherapist and had three children, but I decided it was my turn to learn and grow. When I returned home to Hood River, Oregon I called the airport and started lessons. Within three months I was the proud owner of a PPL.

I love seeing the fly-over events happening across our country to honor those first responders, medical workers, and essential workers who are serving us during the pandemic. Over the past weeks many of us made our way to get a glimpse of those magnificent jets. I do think that seeing some GA airplanes buzzing around might give folks joy right now too, assuming you are safe to do so. If you are able to fly, do so. It will be good for you and who knows, you might inspire someone on the ground to look up how to become a pilot.

When aviation events resume, and they will someday, please consider talking to ADULTS about becoming pilots. Don’t get me wrong; I will always talk to kids about becoming pilots and mechanics. But think about it for a moment, the seven year old you are talking to will have a ten year lag before they can become licensed. However that child’s mother, father, or even grandparent could start flight lessons right away given some motivation. Imagine if Pia never ran into the flight attendant who told her she could become a pilot.


I got my license when I was 40 years old, and in 2020 I will complete my commercial and commercial multi-engine add on. The first 40 years of my life were awesome. I earned my degrees, had my children, and bought my first home. I believe the second half of life can be more exciting than the first.



Pilots make up 2/10 of 1% of the population.

Let’s work together to increase that number and land our dreams.



Jolie Lucas makes her home on the Central Coast of CA with her mini-Golden, Mooney. Jolie is a Mooney owner, licensed psychotherapist, and commercial pilot. Jolie is a nationally-known aviation presenter and aviation writer. Jolie is the Region 4 Vice President of the California Pilots Association. She is the 2010 AOPA Joseph Crotti Award recipient for GA Advocacy. Email: [email protected] Web: Twitter: Mooney4Me

Fix It Now!

Sometimes I just can’t fathom what makes aircraft owners do some of the things they do. Particularly amazing to me are some of the mechanical problems that aircraft owners elect to live with rather than fix.

Now I’m just as averse to spending money as the next guy (and probably more than most). In fact I’ve made something of a crusade out of saving money on aircraft maintenance, and for the past 10 years my company has helped aircraft owners save millions of dollars by avoiding unnecessary and excessive maintenance.

On the other hand, when it comes to my own airplane, I have always had something close to a zero-tolerance policy about mechanical problems. When something isn’t right on my bird, it drives me nuts until I fix it. Almost always, I fix such problems right away rather than putting them off.

My five decades as an aircraft owner has taught me that it’s usually cheaper to fix a problem sooner rather than later…sometimes a great deal cheaper. Not to mention that continuing to fly with a known mechanical deficiency can sometimes be hazardous to your health as well as your wallet.

Fuel LeakFuel leak

Some aircraft owners apparently don’t share my fix-it-now philosophy. Check out this email that I received from an aircraft owner:

Shortly after I bought my airplane last year, I noticed a drip coming from under the aircraft which pooled just to the left of the nosewheel. The drip occurred with the frequency one drip probably every five seconds while the aircraft sat static with the fuel selector on either the left or right tank. Obviously one of the very important shutdown tasks for me was to turn the fuel selector off in order to stop the leak. I never established whether the fuel leaked while the engine is running.

After not flying for the past month, I went out to my airplane last week. The aircraft was leaking fuel despite the selector being in the off position. There was a big pool of avgas beneath the airplane, and the fuel gauges indicated that I had lost almost all the fuel in my tanks…at $4.75 a gallon!

Not understanding why the fuel now leaked regardless of fuel selector setting, I started the aircraft, taxied it around to warm-up the engine and then left it at the maintenance hangar.

I am being told by the very competent maintenance supervisor that originally it was simply a fuel selector gone bad. However, they are now telling me that given that the aircraft now leaks in any position, it’s also a bad engine driven fuel pump. Usually I’d say let’s fix the selector and see if that resolves the problem altogether but I am concerned about the fuel pump going out at some critical time. Please advise.

Here we have an owner who knowingly flew his airplane for a year with a known significant fuel leak in the engine compartment. He only brought it to the attention of his mechanic when he could no longer stop the leak when the aircraft was parked by turning off the fuel selector. Now he’s asking whether it would be okay to fix the fuel selector and continue flying with the fuel leak in the engine compartment unaddressed.

Good grief! I cannot imagine operating my LAWNMOWER with a known fuel leak, much less my airplane. What is this owner thinking?

Exhaust LeakExhaust leak?

While still scratching my head over that one, I heard from the owner of a cabin-class pressurized twin Cessna that made me start scratching my head again:

I don’t push the engines hard, running at 65% power or lower most of the time. However, despite a published service ceiling of 27,000 feet, the engines really don’t perform well over 15,000 feet. I routinely fly over that altitude, but the cylinder head temperatures get a little high, and the engines burn more oil.

Sometimes I have trouble with the wastegates functioning properly at altitude, too, and I get some bootstrapping of manifold pressures (needle separation), which is unpleasant at best (because the props get out of sync), and is dangerous at worst (because the bootstrapping could be due to an exhaust manifold leak). So as a practical matter, I only climb over 21,000 if it is absolutely necessary.

It baffles me how this owner can be sufficiently knowledgeable to recognize that his aircraft has a turbocharging problem that prevents it from operating properly at altitude, and even understands that the problem could well be due to an exhaust leak, yet continues to fly the aircraft with that known deficiency.

Doesn’t he understand that turbocharged twin Cessnas have a ghastly history of exhaust-related accidents, many of them fatal? Doesn’t he know about AD 2000-01-16 that requires repetitive inspection of his exhaust system every 50 hours, and pressure testing at every annual inspection? What is this owner thinking? (For that matter, what is his mechanic thinking?)

Starter drive adapter slipping

The beat goes on. Here’s a post I saw on a popular Internet aviation forum:

On my departure from Pensacola on Sunday afternoon, I turned the key to start the engine (a Continental IO-520) and I could hear the starter motor, but the prop wouldn’t turn. It did twich slightly, but then just sat there.

I have noticed frequently in the past that the prop turns a little and then stops and then a second or two later it continues. Once the prop starts turning, the engine usually fires on the first turn and starts right up.

On my previous airplane, my A&P told me to turn the prop until I hear the click and it would help to start. So, I turned everything off, got out of the plane and turned turn the prop by hand until I heard it click. I turned it again until I heard it click a second time just for good measure. I then got back in the plane and it fired right up like normal.

When I stopped for fuel at Zephyrhills on the way home, the engine started right up with out having to do the prop trick.

I figured I would monitor it and if it acted up again to call in my A&P for a surgical procedure, but after thinking about it this morning I thought I would come to the forum here and see what others have to say.

Continental Starter Drive Adapter

Replies to this owner’s post explain that he was suffering from the classic symptoms of a Continental starter drive adapter (SDA) that is severely worn and slipping. What bothers me is that the owner’s description makes it obvious that he’s been aware of this slippage problem for a long time yet did nothing about it. Even after the slippage got so severe that he nearly found himself stranded in Pensacola, his first thought was to “monitor it” and only bring it to the attention of his A&P “if it acted up again.”

This owner’s approach was clearly to do nothing about the SDA slippage until it becomes so bad that he simply cannot tolerate it any more. This is truly a “penny wise, pound foolish” attitude because every time a Continental SDA slips, it “makes metal” inside the engine. If the owner is lucky, most of that metal will be caught by the oil filter and won’t circulate through the engine and contaminate the bearings and plug up the small passages in the hydraulic valve lifters. If he’s not so lucky, he could find himself buying a $30,000 engine overhaul.

Yet this owner is hardly alone. Countless owners of Continental-powered aircraft have slipping SDAs, but elect to live with the problem until it gets completely intolerable, rather than fix it. That’s not smart.

Fix it now!

I could go on and on, but I’m sure you’ve got the idea. Any time you become aware of something on your aircraft that isn’t quite right, the smart thing to do is to bring it to the attention of your mechanic pronto. If the mechanic agrees that the problem is one you can prudently defer fixing until the next scheduled maintenance cycle, fine. But it’s often the case that the fix-or-defer decision is a “pay me a little now or pay me a lot later” proposition.

An exhaust leak at an exhaust riser flange might be solved with a simple gasket if addressed early. If left unaddressed until the cylinder exhaust flange has been severely eroded, the jug will probably have to come off for expensive rework or replacement.

A slipping Continental starter drive adapter if caught early can usually be fixed for several hundred dollars or so by installing an undersize spring. If allowed to continue slipping until the shaftgear is worn beyond limits, you’re looking at thousands of dollars to repair—or if you get unlucky, a new engine.

A fuel leak caught early can often be fixed by tightening a B-nut or replacing a chafed line. If ignored, it can cause a fire, loss of the aircraft, and perhaps even loss of life.

So, don’t just scribble the discrepancy on a post-it note so you can squawk it at the next annual inspection. Fix it now—or at least discuss it with your mechanic before making a fix-or-defer decision. That’s the smart thing to do.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).

I have more than I need, so I give back

Many of us have friends on Facebook that we follow but may have never met in person. Such is the case for Joshua Knowlton and me. It all started with Oregon and airplanes, but my esteem for Joshua has grown over the years so I want to tell you about him. He is 40 years old and has been working in aviation for about 7 years. He has been an A&P for 5 years, and an IA for 2 years. He says, of his careers, “I dropped out of high school when I was 16 and didn’t go to college until I was 32. I have worked in a slaughterhouse, I’ve been a professional cook, a sewing machine technician, a painter, and I drove a tow-truck for 7 years before starting college. “

He attended Lane Aviation Academy at Lane Community College in Oregon and was awarded several scholarships and finished first in his class with a 4.02 cumulative GPA. He started working at PJ Helicopters soon after graduation from A&P School and worked there for a little over 3 years. After that he started working with his friend and fellow alum Kyle Bushman, restoring antique airplanes. “Since I have my own 1942 Piper L4A Grasshopper that I am restoring I thought this would be a good transition. We worked together for about a year before I decided to get back into rotor craft since I was so attracted to them. I started working for Hillsboro Aviation about a year ago. That is where I currently work and I love my job”, he says.

Joshua is a humble person when talking about his work as a philanthropist. He probably would bristle at me calling him that. He states simply, “I am in a position now where I feel like I have more than I need and I want to be able to give back. This is why I am trying to do good and help others and raise money for causes I support.” I remember he posted on Facebook saying he wanted to take his daughter and her school friend to Disneyland. That quickly turned in to her school friend and her two sisters who were all homeless. He was able to raise over $1800 to help pay their expenses and had a fabulous time at Disneyland. If that isn’t philanthropy I don’t know what is.

After that he decided to start his own scholarship at the A&P school that he attended. “I wanted to pay for one student’s written FAA mechanic exams (about $500) but after talking to a couple of people I raised $300 from them and decided to pull a couple hundred more dollars out of my pocket and pay for the written exams for two students” he says. He calls this scholarship the “Anna Marie Shurden Scholarship for Positive Change”, named after a fellow student who beat the odds and overcame many personal difficulties to finish school and get a job in the aviation industry and continues to be a success. His goal for 2019 is to raise enough money to pay for both the oral and practical exams as well as the written exam for one deserving student. The link for the fundraiser for 2019 is:

Joshua says, “I would like to point out that I am a member of Women in Aviation and my scholarship is geared toward (but not exclusive to) females that are pursuing a career in aviation maintenance. I am a firm believer that this industry needs more women. Not just pilots but mechanics also. “

Joshua was poor as a kid and didn’t have a lot of opportunities. He’s never been out of the country. “Aviation has given me the life I always wanted and has given me opportunities that I never thought I would have. Whenever I have the chance I want to help out other people who are in the place where I was. They just need a hand up to get to a better place and have a chance at the life they have always wanted. I do my best. I am grateful. I work hard.” Be like Joshua.


Jolie Lucas makes her home on the Central Coast of CA with her mini-Golden, Mooney. Jolie is a Mooney owner, licensed psychotherapist, and commercial pilot. Jolie is a nationally-known aviation presenter and aviation writer. Jolie is the Region 4 Vice President of the California Pilots Association. She is the 2010 AOPA Joseph Crotti Award recipient for GA Advocacy. Email: [email protected] Web: Twitter: Mooney4Me

Think like an upside down wedding cake: three-tiered airport advocacy works

Unique airplanes on display at AOPA,Norman

Having just returned from Norman Oklahoma and the AOPA Regional Fly-In I was impressed to see the record attendance numbers at the two-day event. Over 7500 people and 500 airplanes came to enjoy the Friday educational seminars and the Saturday events. This year, AOPA broke the mold of the wildly successful regional fly-in by adding Friday seminars, which educate both the pilot, and non-pilot (as with Pilot Plus One/Right Seat Ready). In observing the event at Norman, I was reminded of the three-tiered model of airport advocacy. In action were local pilot groups, the eleventh annual Aviation Festival, the University of Oklahoma, state-level aviation associations, and of course nationally AOPA.

Jan Maxwell, co-founder Right Seat Ready! companion seminar.

As pilots, we are all used to looking at Class B airspace as an upside-down wedding cake. We understand that the first level extends from the ground upward; a larger ring sits on top of that, and a still larger ring above that. I have long believed that in terms of airport advocacy we need to subscribe to a three-tiered model. Much like Class B, we have the central core being the boots on the ground, local level. Above that are the state level and finally the national level. Let’s take a closer look:

Tier 1 – Local Advocacy: Local wisdom is the best source of information at an airport. Who better understands current issues, history, and future needs better the pilots who are based there? What can you do locally?

  • Join your local airport organization.
  • Find out who your AOPA ASN volunteer is.
  • Attend Airport Land Use Meetings.
  • Host community events at your airport.
  • Form a business relationship with your City or County Planners.
  • Attend all City or County sponsored airport meetings.
  • Attend Airport meetings.
  • Look for chapters of state aviation organizations in your town/area/region.
  • Use media to the airport’s best interest [newspaper, radio, social media, TV].
  • Create a good working relationship with your airport manager.

 Tier 2 – Statewide Organizations: Not every state has its own general aviation organization. But a quick Google search will tell you if your state does. Statewide airport advocacy organizations are important because they maintain statewide contacts, information, and strategies. Further, our statewide groups can also advise and assist the local airport groups when issues arise.

Tier 3 – National Organizations: Our national aviation organizations are a critical piece of the three-tiered airport defense strategy. Membership insures that each maintains its ability to support statewide or local airport/pilot organizations. If you do not belong to AOPA, EAA, NBAA, you should. Critical to interfacing with our congressional representatives, lobbying that national pilot organizations provide a large presence in Washington, DC. This voice serves to remind DC of the importance of general aviation to the nation’s transportation infrastructure.

As a resident of California, I get the pleasure of seeing the three-tiered model in full effect coming up October 13th and 14th at historic San Carlos Airport [KSQL]. The California Pilots Association  in conjunction with the San Carlos Airport Association is presenting AirFest 2017. The two-day event sponsored by ACI Jet,  features a Friday night wine and food reception with AOPA President, Mark Baker. Saturday’s workshops range from safety seminars and airport advocacy to disaster preparedness. All three levels of local state and national are working together to provide educational, social and advocacy.  I would encourage everyone to think like an upside down wedding cake when it comes to advocating for GA and airports. Think globally and act locally. The more we promote general aviation the more we protect our airports.

CalPilots Airfest 2017




Jolie Lucas makes her home on the Central Coast of CA with her mini-Golden, Mooney. Jolie is a Mooney owner, licensed psychotherapist, and commercial pilot. Jolie is a nationally-known aviation presenter and aviation writer. Jolie is the Region 4 Vice President of the California Pilots Association. She is the 2010 AOPA Joseph Crotti Award recipient for GA Advocacy. Email: [email protected] Web: Twitter: Mooney4Me

It’s Baffling

The email from a Cessna T210 owner read:

Suggested baffle holes

The owner of this T210 suggested making some baffle modifications to improve cooling of cylinders #5 and #6 by “giving them more air.” This would NOT have been a good idea, and would almost certainly have made things worse instead of better.

I recently had my engine rebuilt and had a new baffle kit installed. The CHTs for cylinders #5 and #6 are always 20ºF to 30ºF hotter than the rest. During climb the difference gets even bigger. Cylinder #5 and #6 CHTs are very difficult to keep below 400ºF during a climb, even with the cowl flaps open and rich mixture. Should I consider giving them some air? On cylinder #6, why not cut one or more holes in the white aluminum baffle in front of the cylinder? On cylinder #5, why not drill one or more holes in the horizontal aluminum plate located behind the oil cooler?

I replied that cutting holes in the baffles was definitely NOT a good idea, and that doing so would undoubtedly make the cooling problems worse, not better. It was apparent that the T210 owner didn’t understand how the powerplant cooling system in his aircraft works, or what the function of the baffles is. He’s not alone—some A&P mechanics don’t fully understand it, either!

Cooling: then and now

Spirit of St. Louis

Early aircraft engines were ‘velocity cooled’ by passing the slipstream over the finned cylinders. However, this simple approach to cooling is simply not practical for today’s high-performance engines and low-drag airframes.

In the early days of aviation, aircraft designers took a simple approach to the problem of cooling aircraft engines. The engines were mounted with their finned cylinders out in the slipstream and cooled by the horizontal flow of ram air. This design is known as “velocity cooling” and was adequate for cooling the low-compression single-row radial engines of the time.

As engines grew more powerful and multi-row radials and horizontally opposed engines went into service, it became obvious that simple velocity cooling wasn’t up to the job. For one thing, cooling was uneven—front cylinders got a lot more cooling airflow than rear cylinders. For another, sticking all those cylinders out in the breeze created horrendous cooling drag. A better scheme was obviously needed.

That better system was known as “pressure cooling” and is the method used in all modern piston aircraft. Pressure cooling is accomplished by placing a cowling around the engine and using a system of rigid baffles and flexible baffle seals to produce the volume and pattern of cooling airflow necessary to achieve even cooling with minimum drag.

What do baffles do?

Cooling Airflow

The heart of a modern ‘pressure-cooled’ powerplant installation is a set of rigid sheet-metal baffles and flexible baffle seals that, together with the engine cowling, divide the engine compartment into two chambers: a high-pressure area above the engine and a low-pressure area below and behind the engine. Engine cooling depends upon the vertical airflow from the upper chamber to the lower one. Cowl flaps modulate the cooling by regulating the vacuum in the low-pressure chamber.

Our modern piston aircraft are powered by tightly cowled horizontally opposed engines. Inside the cowling, a system of rigid aluminum baffles and flexible baffle seals divide the engine compartment into two chambers: a high-pressure area above the cylinders, and a low-pressure area below the cylinders and behind the engine. Cylinders are cooled by the vertical flow of air from the high-pressure above the engine to the low-pressure below it. Cooling airflow is top-to-bottom, not front-to-back.

The volume of cooling airflow that passes across the cylinders is a function of the pressure differential between the upper (high-pressure) chamber and the lower (low-pressure) chamber of the engine compartment.  This pressure differential is known as “delta-P.” Cowl flaps are often used to modulate the cooling airflow. Opening the cowl flaps reduces the air pressure in the lower chamber, thereby increasing delta-P and consequently the volume of cooling air that passes vertically across the cylinder fins.

It’s important to understand that the pressure differential between the upper and lower chambers is remarkably small: A typical high-performance piston aircraft generally relies on a delta-P of just 6 or 7 inches of water—about 1/4 PSI! Aircraft designers try to keep this delta-P to an absolute minimum, because higher delta-P means higher cooling drag.

…and so what if they don’t?

Baffle Seals

Flexible seals are used to prevent air from escaping through the gaps between the engine-mounted sheet-metal baffles and the cowling. To do their job, they must be oriented so as to curve toward the high-pressure chamber above the engine, so that air pressure pushes them tightly against the cowling.

Because the pressure differential (delta-P) on which engine cooling depends is so very small, even small leaks in the system of baffles and seals can have a serious adverse impact on engine cooling. Any missing, broken, or improperly positioned baffles or seals will degrade engine cooling by providing an alternative path for air to pass from the upper chamber to the lower chamber without flowing vertically across the cylinder cooling fins.  (This is precisely what the effect would have been had the T210 owner cut holes in his baffles, which is why I strongly discouraged the idea.)

Probably the most trouble-prone part of the cooling system is the system of flexible baffle seals. These flexible strips (usually high-temp silicone rubber) are used to seal up the gaps between the sheet metal baffles and the cowling. These gaps are necessary because the baffles move around inside the cowling as the engine rocks on its shock mounts.

To do their job, the seals must curve up and forward into the high-pressure chamber, so that the air pressure differential (delta-P) presses the seals tightly against the cowling. If the seals are permitted to curve away from the high-pressure area—not hard to do when closing up the cowling if you’re not paying close attention—they can blow away from the cowling in-flight and permit large amounts of air to escape without doing any cooling.

I recall some years ago inspecting a Cessna TR182 whose pilots had complained of high CHTs. Upon removing the top engine cowling, I immediately spotted the problem: One of the ignition leads was misrouted and became trapped between the baffle seal and the cowling, preventing the baffle seal from sealing against the cowling. The ignition lead had become severely chafed where it rubbed against the cowling, and an A&P had wrapped the chafed area with electrical tape, but failed to reroute the tape-wrapped lead to keep it away from the baffle seal. Clearly that A&P didn’t understand the importance of an air-tight seal between the baffle seals and the cowling. Repositioning the ignition lead solved both the cooling problem and the chafing problem.

Another common problem is that seals may develop wrinkles or creases when the cowling is installed, preventing them from sealing airtight against the cowling and allowing air to escape. It’s important to look carefully for such problems each time the cowling is removed and replaced, and especially important when new seals have been installed (as was the case with the T210).

Intercylinder Baffles

Inter-cylinder baffles are oddly-shaped pieces of sheet metal that mount beneath and between the cylinders, and force the down-flowing cooling air to wrap around and cool the bottom of the cylinders. (This photo was taken looking up from the bottom of the engine, with the exhaust and induction systems removed to make the baffle easier to see.)

Yet another trouble-prone part of the cooling system is the inter-cylinder baffles. These are small, oddly-shaped pieces of sheet metal mounted below and between the cylinders. Their purpose is to force the down-flowing cooling air to wrap around and cool the bottom of the cylinders, rather than just cooling the top and sides. These baffles are difficult to see unless you know exactly where to look for them, but they are absolutely critical for proper cooling. It’s not at all uncommon for them either to be left out during engine installation or to fall out during engine operation. Either way, the result is major cooling problems.

Awhile back, I noticed that the #3 cylinder of the right engine on my Cessna 310 was running noticeably hotter than its neighbors. I removed the top cowling from the right engine nacelle and carefully inspected all the aluminum baffles and rubber baffle seals, but couldn’t find anything awry. Frustrated, I removed the lower cowlings so that I could inspect the underside of the engine. Sure enough, I discovered that the intercylinder baffle between cylinders #1 and #3 had vibrated loose and shifted about 1/4 inch out of position, creating a significant air leak near the #3 cylinder. Repositioning the baffle properly and tightening its attach bolt to hold it securely in place against the cylinders and crankcase solved the problem.

Why the T210 engine ran hot


Close-up of a fairly significant cooling air leak due to a wrinkle in a flexible baffle seal. This problem was apparent only with the top cowl installed, and could be seen by inspecting through the front intake openings using a flashlight. It’s an excellent idea to look for such baffle seal problems during preflight inspection.

With this as background, I emailed the T210 owner to discourage him from cutting holes in his baffles, and suggested instead that he examine his baffles and seals for existing holes and gaps that could be plugged up to improve cooling. A couple of days later, the owner emailed me back a series of digital photos showing a half-dozen air leaks that he found in his newly installed baffles.

One of those photos revealed a fairly significant cooling air leak due to a wrinkle in a flexible baffle seal. This problem was apparent only with the top cowl installed, and could be seen by inspecting through the front intake openings using a flashlight. Savvy pilots who understand the importance of baffles and seals look for this sort of thing during pre-flight inspection. (Since mechanics do most of their inspecting with the cowlings removed, problems like this sometimes escape their detection.)

I studied the photos and continued my email dialog with the Cessna owner. Between the two of us, we managed to identify a dozen leaks in the T210’s new baffle system. Some were small, others more serious. Combined, they accounted for a significant loss of cooling efficiency. With a few well-placed dabs of high-temp RTV sealant and a little trimming of the flexible seal strips, the owner plugged the leaks in short order, and his engine began running noticeably cooler.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).

Why change the oil?

Aeroshell W100 PlusContinental and Lycoming tell us that we must change the oil in our engines every 50 hours or 4-6 months, whichever comes first—and that’s if we have a full-flow oil filter installed. If we have only an oil screen, then the oil change interval goes down to 25 hours. Did you ever wonder why we need to change the oil so often?

It’s not because the oil breaks down in service and its lubricating qualities degrade. The fact is that conventional petroleum-based oils retain their lubricating properties for a very long time, and synthetic oils retain them nearly forever.

Consider, for example, that most automobile manufacturers now recommend a 7,500-mile oil-change interval for most cars and light trucks. That’s the equivalent of 150 to 250 hours of engine operation. In fact, oil analysis studies have shown that a synthetic automotive oil like Mobil 1 or Amsoil can go 18,000 miles without appreciable degradation, and that’s the equivalent of 400-600 hours.


No, the reason we change oil in our aircraft engines every 25 to 50 hours is not because it breaks down. It’s because it gets contaminated after 25 to 50 hours in an aircraft engine. In fact, it gets downright filthy and nasty.


Dihydrogen monoxide (DHMO) is a highly corrosive chemical that is produced in copious quantities during combustion, and can cause great harm to costly engine components when it blows by the piston rings and contaminates the engine oil. You may be more familiar with DHMO’s common chemical formula: H2O.

Compared with automotive engines, our piston aircraft engines permit a far greater quantity of combustion byproducts—notably carbon, sulfur, oxides of nitrogen, raw fuel, partially burned fuel, plus massive quantities of the corrosive solvent dihydrogen monoxide or DHMO (see graphic)—to leak past the piston rings and contaminate the crankcase. This yucky stuff is collectively referred to as “blow-by” and it’s quite corrosive and harmful when it builds up in the oil and comes in contact with expensive bottom-end engine parts like crankshafts and camshafts and lifters and gears.

To make matters worse, avgas is heavily laced with the octane improver tetraethyl lead (TEL), which also does nasty things when it blows by the rings and gets into the crankcase. (If you’re as old as I am, you may recall that back before mogas was unleaded, the recommended oil-change interval was 3,000 miles instead of 7,500 miles.)

So one of the most important reasons that we need to change the oil regularly in our Continentals and Lycomings is to get rid of these blow-by contaminants before they build up to levels that are harmful to the engine’s health.


Another reason we need to change the oil regularly—arguably even more important than disposing of contaminants—is to replenish the oil’s additive package, particularly its acid neutralizers. When sulfur and oxides of nitrogen mix with DHMO, they form sulfuric acid and nitric acid. If you remember these dangerous corrosives from your high school chemistry class, then you’ll certainly appreciate why you definitely don’t want them attacking your expensive engine parts.

OIl analysisTo prevent such acid attack, aviation oils are blended with acid neutralizer additives. These are alkaline substances that neutralize these acids, much as we might use baking soda to neutralize battery acid. These acid neutralizers are consumed by the process of neutralizing acids, so it’s imperative that we replenish them before they get used up to an extent that might jeopardize our hardware. Of course, the way we replenish them is to change the oil.

How can we tell when the acid neutralizers in the oil have been used up? It turns out that there’s a laboratory test that measures the level of unneutralized acid remaining in the oil. This is known as the “total acid number” or “TAN” test. Some oil analysis firms can perform this test on your oil samples. However, it’s not routinely done as part of the normal oil analysis report, so you need to specially request a TAN test when you send in your oil sample (and be prepared to pay extra for it).


Tach w/hourmeterMost owners don’t bother with the hassle and expense of TAN testing, and simply change their oil at a conservative interval that’s guaranteed to get the junk out and fresh additives in before anything untoward is likely to occur.

On my own airplane, what I do (and generally recommend to my clients) is to change the oil and filter every 50 hours or 4 calendar months, whichever comes first. This means that operators who fly at least 150 hours a year can go 50 hours between oil changes, but operators who fly less will use a proportionately reduced oil-change interval.

This recommendation assumes that the aircraft has a full-flow (spin-on) oil filter installed, that it operates primarily from paved runways, and that it has decent compressions and relatively low blow-by past the rings. Engines that have only an oil screen (no filter) should have the oil changed every 25 hours. Engines that operate in dirty or dusty conditions and ones that have high oil consumption due to high blow-by should have more frequent oil changes.

My friend Ed Kollin—lubrication engineering wizard who used to head Exxon’s lubrication lab and who developed ASL CamGuard—is even more conservative. He preaches that oil should be changed no less frequently than every 30 hours, and frowns when I suggest that it’s okay to go to 50 if you fly a lot.


InsolublesAnother important indication of oil condition can be found in standard oil analysis report provided by some labs—notably the one I prefer, Blackstone Laboratories in Ft. Wayne, Indiana—is the “insolubles” test. This test is performed by placing the oil sample in a centrifuge to separate out all solids and liquids in the sample that are not oil-soluble.

Virgin oil normally contains no insolubles. The insolubles found in drained engine oil come from three sources: (1) oxidized oil that breaks down due to excessive heat; (2) contaminants from blow-by of combustion byproducts; and (3) particulate contamination caused by poor oil filtration. If your oil analysis report reveals above-normal insolubles, it might be indicative of an engine problem—high oil temperature, excessive blow-by, inadequate filtration—and almost certainly means you should be changing your oil more frequently.

By the way, did I mention that I’m a huge fan of laboratory oil analysis? I use it religiously, recommend it strongly to all piston aircraft owners, and believe that it’s one of the most important tools we have—along with oil filter inspection and borescope inspection—for monitoring the condition of our engines and determining when maintenance is necessary.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).

Scope That Jug!

continental-cylinder-removalIn 2002, I did something unfortunate: pulled a perfectly good cylinder off of one of the engines of my Cessna 310. If I had it to do over again, I wouldn’t have touched the cylinder. But at the time, I thought I was doing the right thing.

It was the usual story. I had just downed the airplane for its annual inspection, and the first items on my checklist were performing a hot compression check, draining the oil, sending oil samples to the lab, and cutting open the oil filters for inspection.

All the cylinders had compressions in the low- to mid-70s. All but one, that is. That one measured about 60/80 with air leaking past the exhaust valve.

At the time, the engine manufacturer’s guidance on compression tests was Continental Motors service bulletin M84-15, which instructed mechanics that a jug could leak considerably past the rings and still be considered perfectly airworthy. However, any leakage at all past the valves was considered unacceptable, according to TCM, and required the cylinder to come off for repair or replacement.

So off it came.

Pulling a cylinder is a real PITA. I spent two hours removing cooling baffles and the exhaust and induction plumbing. It took me another hour to remove the rocker cover, rocker shafts, rocker arms, pushrods and pushrod housings. Finally, I used a cylinder base wrenches and a big breaker bar to coerce the eight cylinder base nuts loose. About four hours into the project, I held the offending jug in my arms and carried it over to my workbench to survey the damage.

I inspected the cylinder closely, with special attention on the exhaust valve. Surprisingly, I couldn’t see anything wrong. The valve looked normal, as did the rest of the cylinder. Yet it must have been bad, I thought, because it had clearly been leaking air past the exhaust valve.

I sent the cylinder out for re-valving and honing, installed new rings on the piston, then spent another four hours reinstalling them on the engine and replacing the exhaust, intake and baffles.

Like I said, it was a PITA. It cost me more than $500 plus a full day of sweat equity. (Had I not been doing the grunt work myself, the tab would have been at least $1,500.)

Continental pulls a switcheroo

That episode turned out to be a classic case of bad timing. Had my annual inspection come a few months later, that cylinder would never have been yanked. That’s because not long after my jug came off, Continental radically changed its guidance to mechanics regarding cylinder inspection.

On March 28, 2003, the wizards in Mobile issued service bulletin SB03-3 titled “Differential Pressure Test and Borescope Inspection Procedures for Cylinders.”  This 14-page document is arguably the best guidance ever provided to mechanics on the subject of when a cylinder should be pulled. (SB03-3 was recently incorporated into Continental Motors Standard Practice Maintenance Manual X-0, and is no longer a service bulletin.)

Continental’s guidance in SB03-3 differed from its predecessor M84-15 in two crucial respects. First, it reverses Continental’s previous position that even small amounts of leakage past the valves during a compression check is unacceptable and grounds for pulling the cylinder. Many experienced A&Ps considered the “zero leakage past the valves” standard as being unrealistic and after 19 years Continental finally agreed with that assessment.

The other difference is arguably even more important: For the first time, Continental directed mechanics to perform a borescope inspection of the cylinders at each annual inspection, 100-hour inspection, and any other time a compression check is done. Continental’s language about this is quite emphatic: “Continental Motors REQUIRES a cylinder borescope inspection be accomplished in conjunction with the differential pressure test.”

This was huge.

Although SB03-3 officially applies only to Continental engines, the guidance it offers makes good sense for Lycomings, too.

Borescope choices

Lennox Autoscope

Lennox Autoscope

At the time in 2003, borescopes were expensive and exotic devices whose use was pretty much limited to turbine engine inspections. Relatively few piston GA maintenance shops and A&P mechanics owned a borescope, and even fewer had a clue how to use one or what to look for. In SB03-3, Continental specifically recommended a particular make and model of borescope: the “Autoscope” from Lenox Instrument Company in Trevose, Pa. This was a simple, low-cost rigid borescope developed in the mid-1980s for use by auto mechanics, and cost about $1,000. The Lennox Autoscope had excellent optics and provides a remarkably clear view of what’s going on inside a cylinder. However, it was purely optical, and offered no way to take photos or capture digital images.

Since then, borescopes have become much less expensive and feature-rich. For years, I recommended the BK8000 digital borescope (also about $1,000) which provides excellent image quality and the ability to view images on a screen or capture them as JPEG files on a computer.

Vividia Ablescope VA-400

Vividia Ablescope VA-400

Last year, I purchased a Vividia Ablescope VA-400 from Amazon for less than $200. This is an amazingly inexpensive rigid digital borescope with the unique ability to adjust its viewing angle to anything between 0 and 180 degrees. The unit doesn’t come with an imaging device, but it has a USB cable that can be connected to any notebook computer or Android tablet or phone with a micro-USB port. It comes with both PC software and an Android app. This thing is so cheap that it’s now practical for every aircraft owner to have one.

What to look for

Normal valves

Normal valves

Also A&Ps tend to have little or no training in how to use a borescope, it’s certainly not rocket science. Here’s a photo what valves normally look like. The smaller valve on the left is the exhaust valve, while the larger one on the right is the intake valve. The reddish deposits on the exhaust valve and the brownish ones on the intake valve are typical. These deposits should appear reasonably symmetrical, indicating that the valves are rotating in service as they should be.

Burned exhaust valve

Burned exhaust valve

By way of contrast, here’s a photo of a burned exhaust valve. Note the asymmetrical appearance, especially the highlighted region (white arrows) where the deposits are minimal or absent (because that portion of the valve is running too hot). This is the classic visual signature of a burned valve. If the cylinder leaks air past the exhaust valve during the compression check and if the borescope shows this kind of asymmetrical deposit pattern, you can be relatively certain that the valve is burned and that the cylinder has to come off. But if the valve looks normal under the borescope, some leakage during the compression check is not grounds for removing the cylinder. (Now they tell me!)

Cylinder barrels

Cylinder barrels

The borescope is also a great way to check the condition of the cylinder barrel. Ths photo shows two borescope views of the upper cylinder bore—the so-called “ring step area.” The left view is normal; the right one has abnormal wear and scoring—possibly due to a broken compression ring—and probably needs to come off.

Next time you put your airplane in the shop, ask your mechanic what kind of borescope he uses. If your A&P doesn’t have a borescope or doesn’t know how to use one, educate him (and let him know that it’s now required equipment for any mechanic that works on Continental engines)…or find another mechanic.

Pulling a cylinder without first borescoping it is a lot like performing major surgery without first getting a CT or MRI. Don’t let any mechanic do that to your engine.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).

Checking the Dipstick

Checking the dipstick

There’s a lot more to checking the dipstick than just noting the oil level. The appearance of the oil is at least as important as its quantity.

We’ve been doing it since our earliest days as student pilots. Now that we’re aircraft owners, we still do it as part of our standard preflight ritual. But are we doing it right?

It turns out that there’s a lot more to checking the engine’s oil dipstick properly than just making sure that the oil level is above the minimum-for-flight level listed in the POH. If we really pay attention, we can learn a lot about the condition of our oil and of our engine.

How much oil is needed?

The engines on my Cessna 310 have 12-quart sumps—13 quarts if you include the quart in the spin-on oil filter. When I first acquired the airplane, my mechanic would fill the sump to its maximum capacity at each oil change. It didn’t take me long to discover that the engines didn’t like that, and promptly tossed several quarts out the engine breathers.

My POH states that the “minimum for flight” oil level is 9 quarts. So I asked my mechanic to service the sump to 10 quarts (instead of 12), and I’d add a quart of make-up oil when the level got down to 9 quarts. That worked better, but I was still seeing a fair amount of oil on the underside of the engine nacelles and the outer gear doors.

After I became a mechanic myself and learned about such things, I checked the Type Certificate Data Sheet (TCDS) for my Continental TSIO-520-BB engines, and found that an oil level of 6 quarts was sufficient to make good oil pressure in all flight attitudes from 23° nose-up to 17° nose-down. Armed with this information, I decided to experiment with lower oil levels.

What I discovered was that oil consumption (and the oily mess on the airframe) was drastically reduced if I maintained the oil level at around 8 quarts on the dipstick. Since then, I’ve avoided filling the sump to more than 9 quarts, and I normally do not add make-up oil until the dipstick reads about 7½ quarts. (This still gives me a 1½-quart “cushion” above what the engine needs to operate reliably in all flight attitudes.)

You might wonder why Continental put a 12-quart sump on an engine that requires only 6 quarts. The answer is that FAA certification requirements demand that the engine be designed to hold twice as much oil as it actually needs:

FAR §33.39 Lubrication system.

(a) The lubrication system of the engine must be designed and constructed so that it will function properly in all flight attitudes and atmospheric conditions in which the airplane is expected to operate. In wet sump engines, this requirement must be met when only one-half of the maximum lubricant supply is in the engine.

The TCDS for my TSIO-520-BB engines states that maximum acceptable oil consumption is about one quart per hour. If my engines actually used that much oil, then I’d need to fill the sumps nearly to their maximum capacity to ensure that I had enough oil to make a 5-hour flight without risking oil starvation. But since I know from long experience that my engines use more like 0.1 quart per hour, there’s no reason for me to carry anywhere near that much oil.

Every aircraft engine installation has an optimum oil level at which oil consumption is minimized and the engine is happiest. I would encourage you to experiment to determine what oil level works best for your airplane. Your engine will operate properly at 50% of its maximum oil capacity—guaranteed. As long as you keep the oil level a quart or two above the 50% point, your engine will be happy.

The best time to get an accurate dipstick reading is just prior to the first flight of the day. If you check the oil level shortly after the engine has been run for awhile, the dipstick reading will be noticeably lower because a significant quantity of oil remains adhered to various engine components. Another reading taken 24 hours later will often show an oil level that is ½ to 1 quart higher.

Oil consumption?

Having assured yourself that there’s enough oil in the engine, your next task is to make note of how much oil your engine is using. Keeping track of oil consumption—particularly any significant increase in oil consumption rate—is an important tool for monitoring engine condition.

The most common method of measuring oil consumption is to record how many quarts of make-up oil are added between oil changes, and to divide the total by the number of hours in the oil-change interval. (For example, if the oil is changed after 50 hours and 6 quarts of make-up oil were added during that time, the average oil consumption rate is 50/6 or 8.3 hours per quart.)

Oil consumption graph

Oil consumption isn’t linear—it accelerates as the oil deteriorates over time. The rate of consumption during the first 10 hours after an oil change is a good indication of engine condition.

However, this approach obscures the fact that oil consumption is not linear over the oil change interval. If you keep track of when you add each quart of make-up oil, you’ll find that less oil is consumed at first, and progressively more oil is consumed as the oil’s time-in-service increases.

The reason for this accelerating oil consumption is that the viscosity of the oil decreases as the oil deteriorates. Mineral oils lose viscosity due to a phenomenon called “polymer shearing” in which the long organic molecules are actually broken apart by mechanical action of the engine’s moving parts. Multigrade oils also lose viscosity because their viscosity-index improvers oxidize when exposed to high temperatures.

The increased rate of oil consumption provides tangible evidence that your engine oil is getting “long in the tooth” and ought to be changed soon.

What does your oil look like?

Whenever you check the dipstick, it’s also important to make note of the oil’s appearance—particularly its color and clarity. The oil’s appearance offers valuable clues to its condition and that of your engine.

Oil color

Color and transparency are important indicators of engine condition. When oil becomes dark and opaque, it should be changed. If this happens rapidly, it suggests that the engine has too much blow-by past the rings, or that oil temperature is too hot.

Fresh engine oil has a light amber color and is so transparent that it’s sometimes hard to read the dipstick level. As the oil remains in service, it gradually darkens in color and becomes progressively more opaque.

The darkening of engine oil is caused by contamination and oxidation. Contaminants include carbon (soot), lead salts and sulfur from combustion byproducts that get past the compression rings and into the crankcase (“blow-by”), as well as any dust or dirt that gets past the induction air filter. Oxidation of the oil occurs when it is exposed to high localized temperatures at it circulates through the engine, and results in the formation of coke. Various oil additives are also vulnerable to oxidation, particularly the viscosity-index improvers used in multiweight oils.

Dispersant additives are blended in the oil to help keep these so-called “insolubles” in suspension in order to keep the engine clean and minimize sludge deposits. As the quantity of insolubles in suspension increases, the oil darkens and becomes opaque.

It is important to note how quickly this darkening occurs. If your oil remains relatively light-colored and translucent after 25 hours in service, you can be reasonably confident that your cylinders and rings are in fine condition and that your oil can prudently remain in service for 40 or 50 hours. On the other hand, if your oil gets dark and opaque after 10 or 15 hours, you’d be wise to change your oil more often—perhaps at 25 hours—and you may want to investigate the possibility that one or more cylinders are excessively worn.

Such rapid discoloration is often a good indicator that the oil is distressed. In one study, 90% of oil that appeared abnormally dark on the dipstick was subsequently found by laboratory analysis to be non-compliant with required specifications. Oil that is dark and opaque from blow-by past the rings is very likely to be rich in acids and other corrosive compounds that can attack your cam and lifters, and that’s probably the #1 cause of engines failing to make TBO. Any time your oil appears dark or opaque, you would be wise to drain it and replace it with fresh oil and a new oil filter, regardless of the oil’s time-in-service.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).

Temperature, Temperature, Temperature

I’ve had wonderful luck with piston aircraft engines throughout my nearly 50 years as an aircraft owner. All the engines on my airplanes have made TBO with minimal maintenance along the way, and in recent years they’ve gone far, far beyond TBO.

For decades, I was convinced that the secret of my success was the fact that I “babied” my engines, typically limiting my cruise power settings to no more than 60 or 65 percent power. I felt that sacrificing a little airspeed in exchange for long engine life and reduced maintenance cost was a good tradeoff.

I’ve come to learn, however, that such “babying” is one way to achieve long engine life, but it’s not the only way. That’s because it’s not POWER that damages out engines—it’s TEMPERATURE. It turns out you can run these engines as hard as you like so long as you are obsessive about keeping temperatures under control.

Or as my late friend, powerplant guru and former Continental Motors tech rep Bob “Mose” Moseley used to say, “There are three things that affect how long your engine will last: (1) temperature, (2) temperature, and (3) temperature!”

It’s all about the heat

CHTOur piston aircraft engines are heat engines. They have moving parts—notably exhaust valves and valve guides—that are continually exposed to extremely high temperatures in the vicinity of 1,500°F and sometimes hotter. Since engine oil cannot survive temperatures above about 400°F, these moving parts must function with no lubrication. They depend on extremely hard metals operating at extremely close tolerances at extremely high temperatures with no lubrication. Aluminum pistons and cylinder heads are also exposed to these very hot temperatures, despite the fact that aluminum melts at about 1,200°F. It’s nothing short of miraculous, and a testament to outstanding engineering, that these “hot section” components last as long as they do.

The key to making these critical parts last is temperature control, and the most important temperature is cylinder head temperature (CHT). Mose monitored and overhauled these engines for nearly four decades, and he swore to me that an engine that is operated at CHTs above 400°F on a regular basis will show up to five times as much wear metal in oil analysis as an identical engine that is consistently limited to CHTs of 350°F or less. “It’s amazing how much a small increase in CHT can accelerate engine wear,” Mose said.

As critical as CHT is, many owners don’t have a clue whether their CHTs are 400°F+ or 350°F-. That’s because the engine instrumentation provided by most aircraft manufacturers is pathetically inadequate. The typical factory CHT gauge looks at only one cylinder, and it’s not necessarily the hottest one. Further, the typical factory CHT gauge often isn’t even calibrated, and its green arc extends up to a ridiculously hot 460°F (for Continentals) or 500°F (for Lycomings). Those numbers may be okay as emergency red lines, but they’re horribly abusive for continuous operation. If all you have is factory gauges, you could easily be cooking your cylinders to death while blissfully thinking that all is okay because the CHT gauge is well within the green arc.

To know what’s really going on in front of the firewall, you have to have a modern multiprobe engine analyzer with a digital readout. Such instrumentation isn’t cheap—figure $2,500 for a single or $5,000 for a twin, installed—but if it saves you from having to replace a couple of jugs en route to TBO, it has more than paid for itself. Installing a digital engine analyzer is probably the best money you can spend on your airplane.

Fuel system setup

MaintenanceFor takeoff and initial climb, we normally are at wide-open throttle, full-rich mixture, maximum RPM (if we have a constant-speed prop), and wide-open cowl flaps (if we have those). So there’s not much we can do from the cockpit to affect CHT during these phases of flight.

What does affect CHT is how our full-power fuel flows are adjusted. Unfortunately, it is shockingly common to see damagingly high CHTs due to improperly adjusted fuel flows, particularly in fuel-injected engines. It is not unusual for the fuel flows to be set wrong from the day an engine is installed, and never to be checked or adjusted all the way to TBO. The owner winds up going through cylinders every 500 hours and never knowing why (or blaming the manufacturer).

In part, the problem lies with mechanics who don’t fully understand how critical it is to test and adjust the fuel system setup on a regular basis. Continental recommends that the fuel system setup on its fuel-injected engines be checked and adjusted several times a year to account for seasonal changes. I’ll grant that’s a bit anal, but most Continental-powered airplanes go year after year without this ever being done, and many shops that maintain these airplanes don’t even have the necessary test equipment to do it.

Even when mechanics do test and adjust the fuel system, they often adjust it wrong. For example, Continental Manual M-0 (formerly SID97-3G) contains a lengthy table that specifies full-power fuel flow as a range (minimum and maximum). The “fine print” instructs mechanics to adjust the full-power fuel flow to the high end of the specified range, but many mechanics miss this subtlety and adjust it to the middle of the range. Experience shows that this is simply not enough fuel flow to keep CHTs cool during hot-weather takeoffs.

Lycoming engines with RSA fuel injection have no field adjustments for takeoff fuel flow. If it’s inadequate, the fuel servo has to be sent in to a specialty shop for bench checking and adjustment.

Then there’s the problem of aftermarket engine modifications. For example, engines that have been retrofitted with Superior’s Millennium cylinders often run higher CHTs than they did with their original factory cylinders. That’s because Millennium cylinders have substantially better “volumetric efficiency” than factory cylinders—in other words, they breathe better. Since they breathe more air during every combustion cycle, they need more fuel to maintain the same fuel/air mixture. The full-power fuel flow marked on your fuel-flow gauge may simply not be high enough if you have Millennium cylinders installed.

Even worse are turbocharged engines with aftermarket intercoolers installed. The intercooler reduces the temperature of the air that the cylinder breathes, making it denser. Denser air demands more fuel to maintain the desired fuel/air mixture, so full-power fuel flow must be increased significantly above original factory specifications. Too often this is not done, and the result is fried cylinders.

Many A&Ps are reluctant to adjust takeoff fuel flow above red-line. However, if you have Millennium cylinders, an aftermarket intercooler, or some other “mod” that allows your engine to produce more power than it did when it left the factory, that’s exactly what must be done to keep your CHTs cool and avoid premature cylinder failure.

Enough fuel flow?

MP and FF guage comboHow can you tell if your full-power fuel flow is adequate? If you’re limited to factory gauges, you probably can’t, at least with any precision. About the best you can to is to watch your fuel flow gauge (if you have one).

A good rule of thumb is to multiply your engine’s maximum rated horsepower by 0.1 to obtain the minimum required fuel flow in gallons-per-hour, or by 0.6 for pounds-per-hour. For example, if your engine is rated at 285 horsepower, your takeoff fuel flow should be at least 28.5 GPH; if it’s rated 310 horsepower, the minimum should be 31.0 GPH. If your takeoff fuel flow is significantly less than this, have your mechanic crank it up. And don’t forget that if you have Millennium cylinders or an aftermarket intercooler, your engine might be producing a few percent more horsepower than what the book says, so it might need a few percent more fuel flow.

Now if you have a digital multiprobe engine analyzer, it’s easy to tell if your fuel flow is adjusted high enough. Just make sure none of your CHTs exceed 380°F during takeoff and climb for Continentals or 400°F for Lycomings. Lower is even better.

What about cruise?

Cruise flight represents the lion’s share of our flying time. Just as in takeoff and climb, it’s essential to keep all our CHTs at or below 380°F (for Continentals) or 400°F for Lycomings during cruise to achieve good cylinder longevity, and lower is even better. There are basically three different strategies for keeping CHTs low during cruise:

  • Baby the engine
  • Operate very rich
  • Operate lean-of-peak

All three strategies work, and conscientious use of any of them will give you a good shot at making TBO with minimum cylinder problems. But each has its pros and cons. Let’s take a closer look.

Engine graph

The mixture that many POHs refer to as “recommended lean mixture” is 50°F rich of peak EGT. As this graph shows, using that mixture results in very nearly the highest possible CHT. To reduce CHTs to the level required for good cylinder longevity, you need to do one of three things: (1) reduce power, (2) operate very rich, or (3) operate lean-of-peak.

Baby the engine

Many POHs talk about operating at three alternative mixture settings: “best power mixture” (~125°F rich-of-peak), “recommended lean mixture” (~50°F rich of peak, and “best economy mixture” (~peak EGT). It turns out that “recommended lean mixture” (~50°F ROP) is just about the worst possible mixture setting for keeping CHT low.  If you look at Figure 1, you’ll see that CHT reaches a maximum very close to 50°F ROP. So if you want to operate at “recommended lean mixture” and simultaneously keep CHT low, there’s only one way to get there: reduce power dramatically (generally 65% power or less). In other words, baby the engine.

Both “best power mixture” (~125°F ROP) and “best economy mixture” (~peak EGT) result in somewhat lower CHTs than does “recommended lean mixture.” At either of these mixture settings, you can usually operate at 70% power or so and still keep CHTs in the acceptable range.

In any of these cases, you’re trading power and airspeed for reduced temperatures and increased longevity. For most of us, that’s a reasonable tradeoff to make.

Operate very rich

But what if you are unwilling to sacrifice power and airspeed? Is it possible to go fast and still keep CHTs low?

Sure it is. We already talked about one way to do this in our discussion of takeoff and initial climb: pour lots of 100LL on the problem. In other words, operate very rich.

How rich? Figure 1 suggests that to reduce CHTs by 25°F, you need to enrich the mixture to about 160°F ROP. For each additional 10°F of CHT reduction, you need to enrich an additional 50°F ROP. Using such very rich mixtures, you can go fast and still stay cool. (This is how Reno racers usually operate.) But before you decide to go this route, consider the downsides.

The most obvious downside is that this strategy is very fuel-inefficient. Compared to “best economy mixture,” the very-rich strategy consumes about 25% more fuel, and reduces range by a similar amount. Advocates of very rich mixtures will tell you that “fuel is cheaper than engines,” but don’t be so sure. At today’s avgas prices, using 25% more fuel in a 300 horsepower engine can cost more than $40,000 over the engine’s TBO, and that’s enough to change out quite a few cylinders.

A second and less obvious downside is that very rich mixtures result in “dirty” combustion with lots of unburned byproducts in the exhaust gas. Operating this way for long periods of time tends to cause deposit buildup on piston crowns, ring grooves, spark plugs and exhaust valve stems. Do it long enough and you could wind up with stuck rings, stuck valves, worn valve guides, and fouled plugs.

Operate lean-of-peak

The third way to reduce CHTs is to lean even more aggressively than the POH recommends and operate on the lean side of peak EGT. Figure 1 shows that you can reduce CHTs by 25°F by leaning to about 10°F LOP. For each additional 10°F of CHT reduction, you need to lean an additional 15°F LOP. Using these very lean mixtures, you can go fast, stay cool, and obtain outstanding fuel economy, all at the same time.

What’s the downside of the LOP approach? The only major downside is that if your engine has uneven mixture distribution among its cylinders, it will usually run unacceptably rough at LOP mixture settings.

Uneven mixture distribution can usually be corrected in fuel-injected engines by “tuning” the fuel injector nozzles to eliminate the mixture imbalances. GAMIjectors are tuned nozzles that are STC’d for the majority of fuel-injected Continentals and Lycomings. Continental now offers its own version of tuned injectors on some of its premium engines.

If your engine is carbureted, you have no injector nozzles to tweak. Most carbureted Lycomings have pretty decent mixture distribution and can be run at least mildly LOP without running rough. Some carbureted Continentals (notably the O-470 used in the Cessna 182) have miserable mixture distribution, making it difficult to run those engines LOP without uncomfortable roughness.

Stay cool!

Whatever strategy you prefer, the important thing is to keep a close watch on your CHTs and ensure that they remain cool. The best way to do this is to install a multiprobe digital engine monitor and program its CHT alarm to go off at 390°F (Continentals) or 410°F (Lycomings). If the alarm goes off during takeoff or initial climb, you’re going to have to get your mechanic to turn up the full-power fuel flow.  If it goes off during cruise, either enrich (if ROP) or lean (if LOP) to bring the CHT down to acceptable levels.

If you don’t have a multiprobe digital engine monitor, install one. The cost of such instrumentation (including installation) is usually less than the cost of replacing one cylinder. Failure to install such instrumentation is a classic case of “penny wise, pound foolish.”

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).

The most dangerous thing in aviation?

AOPAfileToolsThere’s an old joke among aircraft mechanics that “the most dangerous thing in aviation is an aircraft owner with a screwdriver.” (Or a wrench, or a toolbox, or a Swiss army knife…)

For many mechanics, this is no laughing matter. I’ve been advocating owner involvement and participation in maintenance for many years, and I’ve gotten a fair amount of push-back from repair station owners and working A&Ps who think I’m doing aviation a great disservice through this advocacy, and feel strongly that aircraft maintenance should be left strictly to the pros (like them).

It’s not hard to understand where this idea originates. I doubt there exists a working general aviation mechanic anywhere who doesn’t have a few dozen horror stories about owner-performed maintenance nightmares he’s found while working on GA aircraft—automotive hoses used in fuel systems; exhaust leaks patched with fiberglass and epoxy; rat’s-nest wiring full of Home Depot plastic-insulated doorbell wire, Scotch electrical tape, Pep Boys’ automotive crimp connectors and cold solder joints; … well, you get the idea. I’m the first to admit that I, too, have seen stuff like this in airplanes that really made me shudder.

(But then again, I’ve also seen plenty of things done by allegedly professional A&P mechanics that made me shudder. Unfortunately, the fact that someone holds an FAA certificate—whether it be a pilot certificate or a mechanic certificate—is no guarantee that he isn’t a jerk.)

Some of the best-maintained aircraft I’ve ever seen are ones maintained largely by their non-A&P-rated owners. After all, no one is more motivated to do a first-class job of maintenance than the person whose posterior and those of his family are on the line.

Some of the most mechanically magnificent GA aircraft I’ve ever seen are kitplanes entirely built and maintained by their owners. I suspect the average homebuilt is better maintained than the average “professionally maintained” spam can.

Let’s face it: There are plenty of aircraft owners who have the knowledge, skill and desire to work on their own aircraft and do a first-class job. On the other hand, there are also lots of aircraft owners who have little or no mechanical aptitude or inclination. Most readily admit that they are mechanically challenged individuals (a.k.a. “all thumbs”) and happily leave the wrench swinging to the pros at their maintenance shop.

Then there are a small minority of owners who tinker with their aircraft even though they don’t know which end of the screwdriver to hold, and wind up doing things that are illegal and unsafe. These are the folks that A&P jokes and horror stories are made of, but in truth they represent only a tiny minority of owners.

You won’t save money

There are lots of reasons to consider getting involved in swinging wrenches on your own aircraft, but generally saving money isn’t one of them. While the labor rates at maintenance shops aren’t exactly cheap, the fact is that you’d probably take an hour to accomplish what a professional A&P can do in 20 minutes. At least that was my experience when I started swinging wrenches on my airplane more than 15 years ago, and that of several aircraft-owner friends who do their own maintenance. Even though I now have a lot more experience and hold an A&P/IA, I’m still a lot slower than a career mechanic who swings wrenches every day.  As owner-mechanics, we consider ourselves safe, competent and careful … but slow.

Think about it. A working A&P can hang a cylinder on an engine in 20 minutes or so. No big deal—install the base O-ring, pre-oil the barrel, insert the piston into the barrel using a ring compressor, lift the jug into position, slide the wrist pin through the piston and con rod, push the jug over the studs, thread on the hold-down nuts, and then torque them into place.

But when I hang a jug, I spend 20 minutes watching the Continental video just to make sure I remember all the necessary steps (since the last time I hung a jug was three years ago), and another 10 minutes looking up the torque values and torque sequence (stuff any working A&P knows from memory because he changes jugs every week). Then I waste five minutes trying to remember where I put my cylinder base wrenches, and another 15 minutes going next door to borrow a 5.25-inch ring compressor. And so it goes.

In other words, when I swing wrenches on my airplane, my work is careful, meticulous, strictly by-the-book … and pathetically slow. I suspect the same is true of most owner-mechanics who only go through one annual inspection a year instead of dozens.

So unless you value your time at less than one-third of your A&P’s shop rate, you’re money ahead to let him do the work.

So why do it?

Good question.

I owned airplanes for 20 years before I first had any interest in picking up a wrench. I never would have guessed that I’d become involved in aircraft maintenance.

After owning a succession of single-engine airplanes, I bought my Cessna T310R in 1987. Eighteen months later, the A&P who had been doing my maintenance relocated, and the mechanic who took his place was relatively young and inexperienced and made me a little nervous. So when the airplane went into the shop for its annual inspection, I decided to hang around and watch, just for peace of mind.

It wasn’t long before “hang around and watch” turned into “hang around and help.” Lots of mechanics wouldn’t have put up with me, but this one did—in fact, he seemed to appreciate my interest, and was very patient in answering my questions and showing me the ropes of basic aircraft maintenance.

Much to my surprise, I found the hands-on work oddly therapeutic—a sharp contrast to my normal daily routine (“slaving over a hot computer keyboard”). I’ve always enjoyed learning new things (my wife calls me a professional student), and I found myself intrigued by how much there was to learn about aircraft maintenance in general and about my Cessna T310R in particular.

Over the next few years I found myself taking on more and more of the maintenance work myself, under the patient supervision of a succession of A&Ps. Clearly, I was hooked.

As I started doing more and more of my own maintenance, I discovered that my aircraft became mechanically better and better. In my past aircraft ownership experience, my airplanes always seemed to have a few squawks waiting for the next time the plane went into the shop. Now, even though the T310R was by far the most complex airplane I’d ever owned, I discovered that it was virtually squawk-free. When anomalies did arise, I’d find myself fixing them immediately, rather than letting them stack up.

So why consider owner-performed maintenance? In my case, the answer is “satisfaction.” The satisfaction that comes from doing something with your hands; from learning something new and complex; from getting to know a complicated piece of machinery in a way that that cannot be achieved without taking it apart and putting it back together; and from flying a squawk-free airplane that receives the finest maintenance that dedication (not money) can buy.

Getting started

Will aircraft maintenance give you the same kind of satisfaction that it does me? There’s only one way to find out, and that is to try it. Remember, I never thought of myself as a wrench-swinging kind of guy—until I tried it and (surprise!) discovered that I liked it.

Regardless of how you think you feel about aircraft maintenance, I strongly suggest that every aircraft owner go through at least one owner-assisted annual inspection. It’ll cost you a week or two out of your busy schedule (consider it a novel vacation idea), and you’ll learn more about your aircraft’s design, construction and condition than you can possibly imagine. You’ll also learn a lot about yourself. You might discover that you enjoy working on your airplane, maybe even that you’ve got a knack for it. Or perhaps that you hate it and/or have absolutely no aptitude for it.

I also suggest you learn how to do some basic preventive maintenance on your airplane—at least how to change the oil and oil filter, and perhaps to clean, gap and rotate the spark plugs. This involves only a couple of hours of work—even the busiest aircraft owner can do it over a weekend. The real beauty of doing your own oil and filter changes—besides the fact that it saves you the hassle of taking your plane to the shop every 25 to 50 hours—is that it forces you to remove the engine cowlings regularly and get up-close-and-personal with your engine. It’s the sort of inspection that pilots really ought to be doing every preflight, but unfortunately can’t be done on most of today’s tightly-cowled aircraft except at oil-change time. Think of an owner-performed oil change as an “advanced preflight.”

What can you do legally?

The FAA has carved out a broad laundry list of so-called “preventive maintenance” tasks that a pilot-rated owner can perform on his aircraft without requiring supervision or sign-off from an A&P mechanic. The relevant regulation is 14 CFR 43.3(g), which reads:

The holder of a pilot certificate issued under Part 61 may perform preventive maintenance on any aircraft owned or operated by that pilot which is not used under Part 121, 129, or 135.

The definition of “preventive maintenance” appears in Appendix A(d) of 14 CFR Part 43, and most owners are surprised to learn just how much maintenance they’re allowed to do on their own recognizance. As an owner/operator, you’re permitted to:

  • Change engine oil
  • Replace fuel and oil filters
  • Service spark plugs
  • Service hydraulic fluid
  • Service battery
  • Lubricate just about anything
  • Change tires and tubes
  • Grease wheel bearings
  • Service landing gear struts
  • Replace fuel/oil hoses
  • Install safety wiring and cotter pins
  • Replace landing and position lights
  • Repair landing light wiring
  • Replace the battery
  • Remove and replace tray-mounted radios (except DMEs and transponders)
  • Change database cards
  • Paint anything except balanced flight controls
  • Repair upholstery
  • Replace side windows
  • Replace seats
  • Replace safety belts
  • Patch airframe, fabric

…and that’s just what you can do on your own without a mechanic’s supervision.

With the cooperation of your friendly neighborhood A&P, there’s almost no maintenance task you can’t do. Here’s what 14 CFR 43.3(d) has to say about that:

A person working under the supervision of [an A&P] may perform … maintenance, preventive maintenance, and alterations … if the supervisor personally observes the work being done to the extent necessary to ensure that it is being done properly and if the supervisor is readily available, in person, for consultation.

In other words, you can do anything that your A&P will let you do (and agrees to supervise and sign-off). In this context, “supervise” means whatever your A&P says it means—the reg says he has to be available for consultation, but that doesn’t mean he has to watch your every move or breathe down your neck. As you earn the trust of your supervising A&P, he’ll probably let you do more and more of your own work and simply drop by to inspect it once you tell him you’re done.

How do you earn your A&P’s trust? Keep in mind that he doesn’t expect you to be an expert—in fact, coming across like a know-it-all is a good way to scare off your mechanic. What’s most important is to demonstrate to your A&P that you know your limits, and that he can trust you to stop and consult with him any time you’re not absolutely sure of what you’re doing. Exhibit a careful, conscientious and humble approach, and your A&P will probably give you lots of latitude.

So try it. You might just like it.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from in paperback and Kindle versions. (508 pages).
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