Staying Alive in a Two Dimensional World

November 11, 2015 by Markus Lavenson

Winter is coming, so I thought it a good time to touch on an optical illusion called flat light. Though it is more prevalent during winter months, it can occur any time of year.

For VFR flight, we need to see enough of the ground as a reference to control the aircraft and to avoid terrain, which is the problem with this illusion. Those of us who fly in Arctic regions take flat light very seriously, but it can also occur at lower latitudes.

If you haven’t experienced it personally, flat light can be difficult to appreciate. While horizontal visibility may often be very good–like being able to see a mountain range 50 miles away–when looking down one is unable to focus on the ground.  Imagine being able to see the ground, without having the depth perception necessary to determine exactly how far away it really is. In a flat light condition your height above the ground determination may be off by as much as 2,000 feet!

The problem stems from the limitations of how we perceive our world. Our brain acts as a video processor and models an image based on raw data received from the retina via the optical nerve. We only see .0035 percent of the electromagnetic spectrum, visible light in the near ultraviolet class, and that data is badly pixilated with a hole in it. The hole, commonly referred to as the blind spot, is due to a lack of light receptors where the optic nerve attaches to the retina. Even when we close one eye we don’t see the blind spot because our brain is very good at interpolating data. It simply fills in the picture with what it calculates should be there. An interesting experiment demonstrating the brain’s imaging capability is when people are fitted with special glasses, turning the images they see upside down. After a time, the brain makes the correction and everything is right side up.  That is until the glasses are taken off, when the image once again goes upside down until the brain can once again adapt.

If that wasn’t problematic enough, the best part of our field of view with good resolution is very narrow. Based around the retina center, it is about 1 degree, or about an inch using the distance from the pilot to the aircraft instrument panel. Now you know why our instructors always stressed a proper scan! As humans, we are stuck with these sensory capabilities, which unfortunately don’t serve well flying in a flat light environment.

Flat light typically occurs during winter with overcast skies and a snow-covered ground. The combination of a very reflective white surface and a lack of direct sunlight turns our 3-dimensional world into one that looks 2-dimensional. There are no shadows or contrast, which are necessary for depth perception. Rock, trees, rivers, buildings, and roads can all provide the pilot with a much needed depth reference. Knowing this, a prudent pilot flying over a large flat white valley may opt to fly along an area with objects providing contrast, such as a rocky ridgeline.

One of the things that makes flat light so dangerous is its insidious nature. The pilot thinks he can see the ground and judge the altitude. Others may be convinced that if it’s daytime and there isn’t a ground obscuration, such as fog or blowing snow that they will be able to see the ground well enough to avoid crashing into it.


Loss of direct sunlight due to an overcast cloud layer over flat terrain covered with snow results in ideal conditions for flat light.

Losing sunlight over flat terrain covered with snow is an ideal conditions for flat light.

The closer one is to the ground the more dangerous the situation, as during takeoffs and landings.  You may have just landed on snow covered terrain with the sun shining, only to find 15 minutes later the sun has dipped below a ridge or been covered by a passing cloud.  You are now enveloped in a shadow of flat light where an attempted takeoff could be very dangerous. This is a case where you are better off being on the ground wishing you were in the air, rather than being in the air wishing you were on the ground.

There was an incident in 1999, when a company crashed three helicopters in one day and all on the same glacier due to flat light. The first helicopter encountered flat light on the glacier and experienced a hard landing, injuring the pilot and passengers. With the first aircraft overdue, a second helicopter was dispatched to search, which also crashed on the same ice field. A third helicopter began to search for the two missing aircraft, which also ended up crashing on the same glacier. The pilot of the third helicopter reported that he thought he was 500 feet above the ground when the aircraft impacted the ground.

These were experienced pilots who had been flying tours over this glacier day after day. They didn’t become less experienced in a day and the glacier didn’t change. What changed were the lighting conditions. It can be hard to accept that at times one can see the ground without enough depth perception to know how far below it really is. Without instrumentation such as a radar altimeter or TAWS (terrain avoidance warning system), the pilot won’t even realize it’s happening.

Anywhere, anytime

Vermilion Bay, on the shores of Louisiana, is so notorious with Gulf of Mexico helicopter pilots that it is commonly referred to as “Vertigo Bay.” The bay’s water has a reddish brown color, and when coupled with an overcast cloud layer, low visibility, and no wind it presents a significant hazard to VFR flight. It is the same effect you get in a room with a full-sized wall mirror when it gives the illusion of the room being much bigger than it really is. Vertigo Bay is so large that with visibility less than 5 miles you can’t see land, and without any wind the highly reflective mirror-like water provides no contrast, but instead reflects the cloud layer from above. When these adverse conditions exist, VFR helicopter pilots circumnavigate the bay sticking close to the contrast of the shoreline.


Highly reflective mirror-like water will reflect the cloud layer from above, making it difficult for the pilot to judge the height visually.  This is the Beaufort Sea north of Alaska, and though the water is reflecting the cloud layer from above, the sandbars, ship and distant ice pack help provide contrast for the pilot.

Highly reflective mirror-like water will reflect the cloud layer from above, making it difficult for the pilot to judge the height visually. This is the Beaufort Sea north of Alaska, and although the water is reflecting the cloud layer from above, the sandbars, ship and distant ice pack help provide contrast.

Avoidance is the certainly the best remedy for flat light. Understanding the environmental conditions where flat light can exist helps the pilot in early recognition and avoidance. Study the terrain along the planned route of flight, including possible areas where you may divert. Review weather reports and forecasts to determine what lighting conditions will exist on the flight. Avoid flying over large expanses of water without wind to ripple the surface and direct sunlight to provide contrast. Stay clear of takeoffs or landings or any low-level flight over large areas of white snow without some direct sunlight. Flat light is a condition where a conservative approach is best, using your superior judgment to avoid the necessity of using your superior skill.

(These views and opinions are my own and do not necessarily reflect the views of Era.)

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I can hear the radios and smell the smoke

October 9, 2015 by Markus Lavenson

Meet Joe Kline.

I first met Kline 15 years ago, and recently had the pleasure of seeing him again. His art brings to life and honors those who lived and died flying the helicopters of the Vietnam War.

Joe is an acclaimed artist painting military aircraft and the people who crewed them. His primary focus is on Army helicopters of Vietnam where he served in the 101st Airborne. His paintings grace the rooms of several museums, including the Smithsonian Air and Space Museum.


Joe’s father was a bombardier on a B-25 Mitchell during World War II, so it was only natural he grew up with a passion for military aviation. During the Vietnam War Joe joined the Army and tested high for a mechanical aptitude. He was assigned to helicopter maintenance unit in Qui Nhon, but he wanted to fly.  Joe soon got his wish and was transferred to Camp Eagle in Hue. He was now in the esteemed 101st Airborne, as a crew chief and door gunner of a Bell UH1 Huey.

While in the 101st Joe saw a lot of action and was involved in the Lam Son 719 offensive in 1971, where 10 percent of the total helicopter losses of the war occurred. While he managed to get some photographs, there wasn’t a lot of time nor was it the place for his artistic talents. The 101st did not encourage nose art on the aircraft, but Joe did manage to design and paint a few unit emblems.

Joe Kline

Joe Kline

Joe now honors those who served by creating historically accurate paintings. He tells me he must be completely accurate, if a rivet is out of place or a control surface in the incorrect position for a particular regime of flight, he will hear about it from someone.

Joe gets the most satisfaction when his art touches people and helps them reconnect. He once painted a Huey, hovering full of ground troops taking an RPG (rocket propelled grenade) while a gunship provided cover from above. Like all his paintings, this was a true event that took place in 1967. It appeared on the cover of Vietnam magazine and was recognized by one of the survivors. The gunship pilot saw the picture and began reaching out to the others.  He eventually reunited with the copilot of the downed Huey, and in turn contacted other survivors of that tragic day.

In addition to reuniting people, Joe gets satisfaction when a veteran stares at his work and quietly says, “I can hear the radios and smell the smoke.”

You see some of Joe’s work at

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The indispensable AFD

October 2, 2015 by Matt Johnson

I’m not talking about the handy little green book that so many of us lugged around for years prior to the advent of wonderful flight apps like Foreflight.

I’m talking about an AFD in a totally different realm of aviation-the Aviation Forecast Discussion. The AFD has become an absolutely indispensable part of my daily and subsequent on-going weather “go-to” resources as a helicopter pilot.

What is it?

For starters, have you ever read a terminal forecast and wondered what the heck were they thinking when they made the forecast? Now you can know exactly what they were thinking. The Aviation Forecast Discussion quite simply is a discussion on the particular elements that made a particular TAF or set of TAF’s for a geographical region. I’m not suggesting this is a new product but in my experience it surely seems to be a great source that many pilots know nothing about. AFDs are issued by each Weather Forecast Office (WFO) and essentially describe weather conditions within their particular region.

As described on the NOAA Aviation Weather Center’s website the AFD, “provides the local office forecaster’s thoughts, reasoning, and uncertainty factors considered for aviation weather, ceiling, and visibility information contained in the TAFs.” Wow! This is a powerful statement. This is more than a TAF that has been “translated” via an app or other software process. The AFD offers insight from the forecaster on why one may see the presence (or lack thereof) of various conditions in a TAF. Additionally, the AFD may very well contain various aviation related weather issues that cannot be encoded into the TAF. Conveniently the AFD is typically generated every 6 hours to coincide with the release of the latest TAF for a particular WFO.

Let’s take a look

Let’s take a look at one example. On a warm summer late afternoon in the Southwestern Ohio Valley this is the colorful radar snapshot of what I saw on the screen.


And this was the most recent TAF for the area:

KCVG 041730Z 0418/0524 25006KT P6SM VCTS BKN050CB
FM050100 VRB03KT P6SM SCT060
FM051300 13004KT P6SM SCT040
FM051900 09005KT P6SM BKN050

By looking at the radar snapshot and the TAF it was obvious the forecaster had some uncertainty about when the storm may move out of the area as indicated by the “VCTS” in the trend section of the TAF and not listed at any particular timeframe.

When going to the AFD for that area and taking a quick read it was obvious why the TAF appeared the way that it did and the radar showed something totally different (for a particular timeframe).

This is what the AFD contained:


BINGO! The AFD told me many things that clarified the current conditions that I was observing. As predicted in the TAF the conditions would in fact improve, but isolated showers and thunderstorms were popping up across the area due to a continued warm and unstable airmass. This made it difficult for the forecaster to be more precise in the TAF as evidenced by the statement, “tough to time the storms in to any of the TAF sites though so will stick with the trend of covering the threat with a VCTS through the daytime period.” What was evident based on the TAF and the AFD was that the thunderstorm activity was dissipating much slower than expected but one could in fact expect improving conditions as it related to the showers and storms. (But note the possibility of “patchy MVFR” and the probability that the same airmass will be in place the following day.) 

How to find the AFD for your area

The AFD can be easily accessed. Simply go to and click on “FORECASTS” and scroll down to “Aviation Forecast Discussion.” From there simply click on the region you are most interested in.

After clicking on your region you will get a textual discussion from that particular WFO giving you an idea of what to expect.

It’s free, it’s basic and just a few sentences from the AFD can give you an idea of the “big picture” of what to expect for a small geographic area.

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The need for speed

September 24, 2015 by Ian Twombly

There was news from AgustaWestland last week that the company’s forthcoming AW609 Tiltrotor broke a speed record from Yeovil, England to Samarate, Italy. The entire 627 nautical miles took two hours and 18 minutes, resulting in an average speed of about 273 knots. That’s a pretty impressive clip.

With the Tiltrotor expected to be in the $30 million range, not to mention a few thousand an hour to operate, the time savings has to be seriously compelling to justify the expense.

Although this flight went between two AgustaWestland facilities, it could just have easily been two customer factories, or a CEO’s home and weekend estate. So it’s as good as any to use as a case study. Alternative modes of getting to the airport would have been required on both ends;  let’s look at how that would work.


Yeovil is served by either Bristol or Bournemouth. Let’s give our alternate method the best chance and say we base a Citation X out of Bournemouth. We bought it used, so we had a bit left over for an Agusta AW109 that we keep at our office. It’s a best-case scenario of helicopter to fastest business jet in the world. We’ll also assume both the jet and helicopter are primed and ready to go.

We can ballpark the flight between Yeovil and Bournemouth at about 130 nautical miles. That would take about 15 minutes. Add in some ground time with the jet and we’re off U.K. soil in about 30 minutes total.

The destination helps traditional airplane travel because the facility is only a few miles from an airport. And given that the Citation X can make this trip in a little over an hour (call it an 70 minutes with a direct routing), things are looking good for jet travel, indeed.

After landing in Milan we have another 15 minutes on the ground before getting in the car for the 15-minute drive to the AgustaWestland facility–our final destination.

A bit of scratch-pad math puts this form of trip at one hour and 55 minutes. Of course, that’s with the world’s fastest business jet, a helicopter, a direct routing, and a destination only 15 minutes from an airport large enough to handle our jet.

No doubt a more traditional trip would involve an hour drive to the airport on the front end (Yeovil to Bournemouth), a slightly slower jet, some diversions in flight, and a longer drive on the back end. In all, it probably takes AW executives more like three hours or more to make that trip.

Thirty million is a big price to pay for saving an hour, but we shouldn’t underestimate people’s needs for aircraft that fit unique mission profiles. The sweet spot for the Tiltrotor is pretty small. The mission has to be long enough that traditional rotorcraft can’t compete, and short enough that a jet won’t blow it away. AW says the Tiltrotor offers rotorcraft capabilities with turboprop speeds. That’s pretty cool. But they also say that executives are the aircraft’s primary target customer, and said executive can buy a jet and a traditional helicopter for a lot less money.

Despite all this there are approximately 60 orders for the aircraft thus far, and barring significant missteps, I think that will increase. Once people see these operating in and out of downtown heliports, factories, and airports, their appeal will grow. I was on an airline flight last week out of Washington National and a V-22 Osprey flew down the Potomac River. People who had moments before been buried in their morning paper took notice. They pointed and made comments. There’s no denying the technology is enticing, and for that reason alone people will buy them. I know I would love to fly it!

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Bell opens new training academy

September 16, 2015 by admin

Bell Helicopter last month celebrated the grand opening of its new training academy in Fort Worth, Texas. Bell has long been known for superb factory training, both for simulation and especially in the aircraft. The facility is equipped with a dedicated tower and flight line, a maintenance training hangar, and advanced multimedia classrooms. The company said its 86,000 square foot facility represents the final part of its consolidation efforts in North Texas.

The academy offers basic, recurrent, and advanced training programs for the entire line of Bell models, including some no longer in production. It also offers non-destructive inspection training for technicians, and first responder safety ground training. Bell also provides offshore and rooftop specific training by way of a 30-foot elevated platform used for pinnacle take-off and landing maneuvers. It is an FAA, EASA and Transport Canada approved training facility. With the training academy now complete, Bell has consolidated more than one million square feet within their main corporate campus which they said will save close to $20 million in annual operating expenses.

Bell CEO John Garrison (foreground) and instructor Ric Forns in a Bell 47 at the grand opening.

Bell CEO John Garrison (foreground) and instructor Ric Forns in a Bell 47 at the grand opening.

Like all helicopter manufacturers, Bell has been hit recently with declining commercial aircraft sales, due in part because of the continued decline of crude oil prices. Military sales of the V-22 Osprey, praised for its performance in Iraq and Afghanistan, have steadily declined as well.  The Osprey is a tilt-rotor aircraft that hovers like a helicopter but can fly at high-altitude and speeds similar to a jet. It can carry two dozen troops and up to 20,000 pounds of additional cargo.

At the same time, the company is looking to the future with its 505 light single, a replacement for the ever-popular 206. Late last month the company officially opened its Lafayette, Louisana-based 505 production facility. Testing continues at Bell’s Mirabel, Quebec location.

–Scott Hotaling

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Runways are for beauty queens

September 2, 2015 by Markus Lavenson

“Hey, is that your helicopter?”

Naturally, he had to be talking to me, being the only one in the room remotely looking like a helicopter pilot. I was wearing a nomex flight suit with black boots, surrounded by corporate pilots decked out in suits and ties. I stood out as much as my Bell 222 out on the ramp with a covey of corporate jets. We both looked out of place at the San Francisco International Airport FBO.

After I said it was, he asked, “How fast does it go?”

I thought jeez here we go again, what is it with jet guys? It’s like an Indy driver asking how fast a four-wheel drive truck can go.

“Oh, she will cruise about 130 knots,” I said. I heard a few snickers around the room from the younger copilots. The older captains seemed bored reading their newspapers.

Okay my turn I thought.  “Which airplane are you flying?” I innocently asked, as he proudly pointed to one of the sleek jets.

“Nice. How slow can it fly?”

“What do you mean?” he asked, somewhat flustered.

“How slow can it fly?” I repeated.

He looked at me a little perplexed and said, “Well, in a landing configuration, we can do about 105 knots.”

“You’re kidding right?  Is that as slow as you can possibly get that thing?” I said with feigned incredulity. I noticed the newspapers being lowered and the captains didn’t look bored anymore.

He said “No, that’s about as slow as they can fly,” looking around the room for a little help.

I said, while nodding my head sympathetically, “That is a severe limitation, but if you stick to runways you should be okay.”

“The helicopter is ultimate off-road vehicle,” I said. “I can put it on a mountaintop, highway, beach, or rooftop helipad anytime of day or night. I can pick up an accident victim having the worst day of her life and fly her to a trauma center in a matter of minutes. That helicopter is a single-pilot IFR capable aircraft that flies about 400 patients a year, and it rarely uses a runway. It isn’t the fast, but the slow that matters in my world.”

We all had a good laugh, and one of the captains said, “Well, nobody in this room is ever going to ask another helicopter pilot how fast their helicopter can fly.”

As I left the room I looked through the window at all the beautiful, though severely limited corporate jets and said, “Runways are for beauty queens.”

Out on the ramp, thinking about the comparison of airplanes and helicopters, I thought back to the 1980s when I had introduced a friend to helicopters for the first time.

We had met flying Beech 18s and a Cessna 182 for a skydiving operation on weekends. He had never been in a helicopter, so early one evening after flying a powerline patrol I took him up for a short ride. I removed the doors, my preferred way of flying in those days, and we enjoyed the cool Carolina air.

After flying around for a bit we returned to the airport and I figured I would demonstrate some of the unique abilities of the helicopter. On final approach to a runway, I bled off airspeed while maintaining altitude at 400 feet. As the airspeed indicator crept lower and lower, my friend sat straighter and straighter in his seat.

I said, “This must feel a little strange to you?”

“Yep,” was all he could muster.

Eventually, he was gripping the sides of the seats in true white-knuckle fashion as the airspeed indicator reached zero. We remained motionless at a high hover, with the runway right in front of us.

“Pretty cool, huh?” I said, as he stared at the airspeed indicator.

He said nothing.

“Isn’t this awesome?” I tried again.

“Everything I fly would be falling out of the sky,”  he replied tersely.

After a minute, I noticed the blood was returning to his fingers. He was relaxing and getting used to the idea that airspeed was totally unnecessary for powered flight. I then lowered the collective slightly, dropped the nose and swooped in a shallow approach profile for the runway doing a quick stop at a taxiway intersection. I then continued down the runway at a hover taxi speed with a couple of 360-degree pedal turns thrown in for practice.

Minutes later, as we air-taxied behind one of the Beech 18s and gently set down on the grass, he said, “Okay, tell me about how long and how much to get my helicopter pilot license.” He had gone from white knuckles to wanting to fly helicopters, and in just a few minutes.

I believe deep down his heart was saying, “Yeah, runways are for beauty queens.”

This is all meant in good fun, and mainly, in awe of our machines. Have a “runways are for beauty queens” story?  Share it below in the comments section.

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No two are the same

August 6, 2015 by Markus Lavenson

Recently Mick Cullen, of the Rotary Wing Show, invited Hover Power editor Ian Twombly and me to a podcast interview (episode 31 if you want to check it out). The end of the podcast had an offer for an AOPA hat, given to the first three listeners who offered topic suggestions for Hover Power. Thanks to Lee Rilea, who asked us to describe: flight characteristics of different helicopter types, and how pilots can prepare for them.

Each model helicopter is a unique and aerodynamically complicated machine, and all have differences the pilot must be cognizant of. Even sister ships have differences, such as the 62-inch versus the 65-inch tail rotor in the Bell 206 series. The differences can be subtle too; simply changing low to high clearance landing gear can alter slope limitations for a particular aircraft.

With proper training and proficiency these aircraft differences are manageable. While the Rotorcraft Flying Handbook is a good general resource, the Rotorcraft Flight Manual and Factory Training Manuals will have specific information for a particular helicopter.

I will cover a few differences, and Hover Power blog readers can add more in the comment section.

Main rotor systems

An example of a unique flight characteristic involving the main rotor is the rigid rotor system of the BO-105, BK117 and EC145. Unlike most other rotor systems, which are semi-rigid or fully articulated, it is capable of negative Gs. Sounds great, but as in most cases there are compromises, and mast bending is one. The rotor blades, rotorhead, and mast are attached together rigidly without hinging capability. Turbulence, abrupt or extreme pilot control input, settling with power, and slope landings can all generate high mast bending. Think of the rotor system, mast, transmission, and airframe as one solid unit without any ability to hinge, with the mast actually bending when there is a shear force between the airframe and main rotor. A strain gauge is mounted inside the mast and is connected to the mast moment indicator on the instrument panel, so the pilot can assure mast-bending limitations are not exceeded.

Let’s also consider Vne and retreating blade stall in the rigid rotor system. Some aircraft are fairly docile when encountering retreating blade stall, just a gentle shutter as the aircraft slowly pitches up or rolls, but not the BO105.

One day, while flying a BO105CBS across the mountains of New Mexico I experienced retreating blade stall in a rigged rotor system for the first time. I had just a few hours in type, but fortunately was flying with an instructor. As one increases altitude, the Vne will decrease accordingly and we had made that adjustment. However, as any mountain pilot can tell you, turbulence and altitude can make for a wicked combination. A strong updraft can momentarily increase the angle of attack on a blade, creating a retreating blade stall condition. There is nothing gentle about this in a rigid rotor system, as I found out that day. We hit a particularly strong updraft at about 7000 feet, when the nose pitched up abruptly. Forward cyclic had no effect, and in fact would not even move. I didn’t recognize this as a retreating blade stall condition, but the instructor did and immediately decreased collective or we probably would have looped. Decreasing the collective removed the stall condition caused by the updraft, and allowed the cyclic to regain its effectiveness. I learned to always have my hand on the collective when flying the BO105 over mountains or when the possibility of turbulence existed. I also learned a smoother pitch attitude could be maintained in the BO105 by actually flying the collective with slight cyclic inputs. Increase collective slightly to pitch up and decrease collective slightly to pitch down, resulting in a smoother ride through turbulence.

Another characteristic of the BO105 is a phenomenon called “divergent roll.” In a descending low airspeed right bank, there is a tendency to run out of left cyclic. When turning right, one needs more and more left cyclic to maintain the bank angle without having it increase. One can reach the point where the cyclic is hitting the pilot’s left leg, which is already pinned against the center console. The remedy is left pedal, which is responsive in correcting this condition. This is not considered a cause for concern among experienced BO105 pilots, because they are prepared and knowledgeable of this characteristic.

The tail rotor and Notar

All helicopters with a tail rotor or Notar (MD Helicopters’ acronym for No Tail Rotor) are susceptible to a loss of tail rotor effectiveness in a hover or at low speed. The effectiveness of the tail rotor is dependent on a stable and relatively undisturbed airflow. There are many factors that can affect this airflow and cause LTE, such as main rotor downdraft and vortices, density altitude, gross weight, turbulence, forward airspeed, and relative wind speed and direction. Some of these factors contribute to the need of increased tail rotor pitch, resulting in a higher power requirement and a higher angle of attack of the tail rotor blades, leaving less thrust available in reserve. Other factors can disturb the airflow through the tail rotor creating a vortex ring state, such as the relative wind direction; also known as the critical wind azimuth. No two model helicopters are alike and the pilot must know the aircraft’s tail rotor limitations, typically found in the limitation and performance sections of the RFM.

A pilot flying at lower altitudes may not give the critical wind azimuth much thought, such as during a hover taxi in a right quartering crosswind. However, an increase in density altitude and gross weight also increases the required pitch from the tail rotor, making it more susceptible to LTE when wind is from the critical azimuth direction.

A different technique may be prudent to account for the increased susceptibility of LTE in certain aircraft. The MD902, with its Notar system, is more prone to LTE than any other aircraft I’ve flown when operating at altitudes over 3000 feet and at high gross weights. When hovering at altitude in the MD902, I would avoid any right crosswinds during takeoff, approach or hover; even to the point of doing a 270 degree turn at a taxi intersection rather than the 90 degree with a right crosswind. It is a manageable characteristic, as one learns “everything is into the wind above 3000 feet” in a MD902.

Another aircraft I’ve flown prone to LTE were the early Bell 206s. These had the smaller 62-inch tail rotor (Bell later went to the 65-inch tail rotor), and the early flight manuals did not have the critical wind azimuth chart or its inclusion in the hover ceiling charts.

HP chart 2

For this BH206, the critical wind azimuth area is depicted to be from 050 to 210 degrees, and the hover chart shows the altitude, temperature, and gross weight that area would be designated the avoid area B.

Gross weight

Lighter helicopters can respond faster to pilot input than heavy helicopters. An acceptable descent rate below 1,000 AGL for an AStar 350 (GW of 4960 lbs) would not be acceptable for an AW139 (GW of 14994 lbs). Just as a heavy truck on a highway needs more time to accelerate and decelerate, so do larger aircraft. The pilot of a heavy helicopter needs to recognize a negative trend sooner, such as an unacceptable descent rate on short final, as it will take more time to correct.

I typically fly out of Houma, Louisiana, which is probably the busiest airport in the United States for civilian helicopter operations, with over 71,457 helicopter landings in 2014. One can watch variations in approaches and departures for different helicopters. The most obvious variables are the approach speed, profile and descent rate. Heavy helicopters, such as the Sikorsky S-92, make a slower and steeper approach than lighter aircraft. Each pilot is flying their specific type helicopter in accordance with the RFM and company flight standards, and it’s a good opportunity to see how this varies among different helicopters.

What differences have you experienced? Tell us in the comments section.

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Putting the auto in autorotate

July 22, 2015 by Ian Twombly

Three seconds. That’s all you the time you have to get the collective buried on an R22—give or take a tenth or two. Now a new company thinks it has an innovative solution that will help keep the air flowing through those rotor blades.

HeliTrak is developing a collective pull down, a simple system that automatically drops the collective in half a second once the low rotor light and horn go off. Much like a stick pusher in a fixed-wing stall, the collective pull down overrides the feeble human brain and uses a motor and a cable to quickly yank it down.

In the event it’s not a true emergency and the pilot elects to figure things out, he can manually override it by doing a bit of tug-of-war. The system is designed to give up and let the human win after about three seconds, the logic being by that point the pilot has figured out it’s not a true emergency and wants to keep flying.

Even if he goes the safe route, lets the system win, and then later realizes it’s ok to keep flying, the system is engineered to let go and allow the pilot to fly again.

I bench tested the collective pull down (meaning it was in a display box on a table at EAA Airventure) and was really impressed. The pull is dramatic, but clearly easy to override in a tense moment. In fact, the whole thing is so simple, so obvious, it’s a short conversation. Seems cool, should be certified, little downside.

HeliTrak hopes to get the STC in the next few months. Initially it will be available for the R22, but the R44, Enstroms, and JetRanger could come soon after. At fewer than two pounds, and a modest three or so hours to install, the initial numbers look good.

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More on “scud running”

July 16, 2015 by Maria Langer

In my post about long cross-country flights I brought up the topic of scud running. Apparently, my account of a flight into low visibility conditions, which I referred to as “scud running,” hit a nerve. As an example, someone called for a “definitive statement from you declaring NO to EVER scud running.” That got me thinking about the reality of flying.

My Definition of “Scud Running”

Let’s start with exactly what I’m talking about when I use the phrase “scud running.” Reader Dan Schiffer nailed it when he responded to one of the commenters. He said, in part:

It’s a term most pilots use to discuss low visibility conditions that we all are faced with occasionally due to changing weather.

To me, scud running is any situation where low ceilings or low visibility require you to alter your route around weather. And yes, low ceilings are a part of low visibility–after all, if you’re in mountainous terrain, don’t low ceilings obscure your visibility of mountainsides and peaks?

The FAA discusses scud running in its Pilot’s Handbook of Aeronautical Knowledge:

This occurs when a pilot tries to maintain visual contact with the terrain at low altitudes while instrument conditions exist.

I discuss this in more detail later, when I cover weather minimums for helicopter pilots.

Neither my definition nor the FAA’s have anything to do with so-called “scud clouds.” I can’t find any mention of these clouds in either the Aeronautical Information Manual (AIM) or Pilot’s Handbook of Aeronautical Knowledge. I did find a definition in AC 00-6A, Aviation Weather:

scud – Small detached masses of stratusfractus clouds below a layer of higher clouds, usually nimbostratus.

A Google search brought up a similar, but more detailed Wikipedia definition:

a type of fractus cloud, are low, detached, irregular clouds found beneath nimbostratus or cumulonimbus clouds. These clouds are often ragged or wispy in appearance. When caught in the outflow (downdraft) beneath a thunderstorm, scud clouds will often move faster than the storm clouds themselves. When in an inflow (updraft) area, scud clouds tend to rise and may exhibit lateral movement ranging from very little to substantial.

For the record, I’m definitely not endorsing flying anywhere near a thunderstorm or cumulonimbus cloud. The FAA says to maintain 20 miles separation from thunderstorms and that’s a pretty good rule of thumb.

So, in summary, when a pilot uses the phrase “scud running,” it usually means flying in low visibility conditions and has nothing to do with so-called scud clouds.



A Note about flying in remote areas

I’ve done just about all of my flying in the west: Arizona (where I learned to fly), Nevada, Utah, Colorado, New Mexico, California, Idaho, Oregon, and Washington (where I now live). In the 3,200 hours I’ve logged, I’d say that at least half of them were in relatively remote areas. Because of this, it’s difficult for me to remember that most pilots fly in more populated areas, where they’re seldom out of sight of a town or building.

As difficult as this might be for some people to believe, there are still many places in the U.S. where a helicopter pilot can fly for over an hour and not see a single sign of human life. I’ve flown 90 minutes in a straight line somewhere between Elko, NV and Burns, OR without seeing a building or a vehicle on one of the few dirt roads–just herds of wild horses running at the sound of my approach. I’ve flown over the high desert of the Arizona Strip, crossing just one dirt road over an 85-mile stretch of forest and canyons. I’ve flown the length of Lake Powell from the Glen Canyon Dam to Canyonlands National Park in the winter, passing just three seasonally closed marinas along the lake’s blue water and canyon mouths. I fly with a SPOT personal tracking device for a reason; if I go down out there–even by choice in a precautionary landing–no one would find me without some help.

So while “scud running” might seem like an unreasonable risk when you’re in an area with towns and airports every five or ten miles, it could be a matter of life and death when you’re out in the middle of nowhere and need to get somewhere safe. It’s not a black and white situation with a right or wrong answer.



Let’s look at an example. Suppose you’ve done all your flight planning and believe you can make a two-hour flight to Point A, which is a rather remote place, without any weather/visibility concerns. You start the flight and things are fine for the first 90 minutes or so. Then the weather starts deteriorating. Maybe the ceiling drops or there are scattered rain showers that lower horizontal visibility in various places along your path. You can see well enough in your general forward direction and easily find paths around those showers that will get you closer to your destination, but things might be worse up ahead. Who knows? Even a call to Flight Service–if you can reach them on the radio in mountainous terrain with low ceilings preventing you from climbing — might not be able to provide adequate weather information if the area is remote enough.

Here’s where experience, judgement, and personal minimums come in. As helicopter pilots, we have three options:

  • Alter your route to completely avoid the weather, possibly ending up at a different destination. This might be the best option if there is an alternative destination and you have enough fuel to get there. But if your intended destination is in a remote place and you’re only 30 minutes out, there might not be an alternative.
  • Land and wait out the weather. Heck, we’re helicopter pilots and can land nearly anywhere. There’s nothing wrong with landing to wait out a storm. Remember, in an emergency situation, you can land if necesary, even in an area where landing is normally prohibited, such as a National Park, National Forest, Wilderness Area. (Again, I’m not recommending that you land in any of these places in non-emergency situations.) Do you have gear on board for an extended or perhaps overnight stay? This is another good reason to bring food on a cross-country flight.
  • Continue toward your intended destination. At the risk of sounding like I’m a proponent of “get-there-itis,” the destination is a known that’s a lot more attractive than the unknowns offered by the first two options.

There are many variables that will determine which option you pick. Here are a few of them:

  • Experience. If you’ve encountered situations like this before, you have a better idea of your comfort level than if you haven’t. You’ve likely also established personal minimums, possibly fine-tuned by real scares. The more experience, the better you’ll be able to deal with the situation and make the right decision.
  • Alternatives. If there is an alternative destination within range that you can safely reach with available fuel plus reserves, why wouldn’t you go for it?
  • Available fuel. There’s a saying in aviation: “The only time you have too much fuel is when you’re on fire.” One of the challenges of planning a long cross-country flight is making sure you have enough fuel on board to deal with unplanned route changes. But when flying to extremely remote areas, you might need almost all the fuel you have on board to get there. That definitely limits your options.
  • Actual weather conditions. If you can see a path ahead of you with potential landing zones and escape routes along the way, you’re far more likely to succeed at moving toward the destination than if the weather is closing in all around you. Never continue flight to the point where you don’t have at least the option to land and wait it out. The trick is to turn back or land before that happens; experience will be your guide. Likewise, if what you’re seeing tells you that the weather is localized and better conditions are just up ahead — perhaps you see sunlight on the ground beyond those heavy showers? — continuing flight might be the best option.

So what’s the answer? There isn’t one. As the pilot in command, you are the decision maker. You need to evaluate and re-evaluate the situation as it develops. You need to make a decision based on your knowledge and experience. If in doubt, choose the safest option.

With mist, rain, and low clouds, would you keep flying?

With mist, rain, and low clouds, would you keep flying?

Weather Minimums

Despite the severe clear weather I’ve been seeing around my home in Central Washington State this week, weather minimums are on my mind lately. Why? Mostly because I just took my Part 135 check ride and was a bit hazy on them. Spending most of my flying career in Arizona didn’t do me any favors when it comes to knowing when it’s legal to fly — or being able to identify different types of fog by name, for that matter.

So let’s look at weather minimums as they apply to helicopters.

FAR 91.155, Basic VFR weather minimums sets forth weather minimums for each type of airspace. I’m going to concentrate on Class G airspace, mostly because that’s the type of airspace I’ve been talking about.

According to the FARs, a helicopter may legally operate under VFR in Class G airspace during the day with a minimum of 1/2 mile visibility clear of clouds. Conditions less than that are technically IMC, thus invoking the FAA’s definition of “scud running” discussed above.

But what if visibility in your desired flight path is 1/4 mile or less but visibility 30 degrees to the right is a mile or more? That is possible with localized showers or very low scattered clouds. Are you allowed to fly? I think that if you asked five different FAA inspectors, you’d get a bunch of different answers. But if you crashed while flying in those conditions, the NTSB report would claim you were flying VFR in IMC.

What’s the answer? Beats me.

Scud Happens

What I do know is this: If all your preflight planning indicates that weather and visibility will not be an issue during a flight but unexpected weather conditions come up, you need to react to them. As helicopter pilots, we’re lucky in that we have options to avoid flying into clouds and the terrain they obscure. At the same time, we don’t want to push that luck and get into a situation we can’t get out of safely. Experience, skill, and wisdom should guide us.

Scud running is never a good idea, but sometimes it’s the best idea under unforeseen circumstances. It’s your job as a pilot to (1) avoid getting into a dangerous situation and (2) make the best decision and take the best actions to complete a flight safely.

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Slinging IFR

June 30, 2015 by Markus Lavenson

Flying helicopters IFR with a sling load presents unique challenges, requiring specific skills of the pilot.  One must obviously be able to control the helicopter without any outside visual references. Less obvious, one must also be able to correctly interpret the instruments, which reflect both the behavior of the load and the orientation of the helicopter. A Class B external load (sling load) is one that is free of the earth’s surface and is attached to the helicopter by a synthetic or wire line. The pilot is “flying” both the helicopter and the load, which at times can seem to have a mind of its own.

Today slinging IFR is not a common practice, though there was a time on the North Slope of Alaska where it was employed regularly. I thought it might be interesting to look at this operation in some detail.


An AW139 lifts off for an external load training flight out of Deadhorse Alaska.  Photo by Dan Adams

An AW139 lifts off for an external load training flight out of Deadhorse Alaska. Photo by Dan Adams


Controlling the sling load

Normally one can see the external load, and make the necessary corrections. Lateral swinging is more common than a fore-aft motion or a circular motion, so we will focus on that. A quick lateral cyclic input towards the load, just as it reaches its apex, moves the aircraft over the load neutralizing its motion. You are essentially moving the aircraft over the load after it has swung out to the side. This dampens the movement of the load and stabilizes it. However, when flying IFR the instruments must be used to indicate the loads’ position and movement. The best way to learn how the instruments reflect the movements of the load is during VFR flight, when the load and gauges can be seen together.

Flying IFR with a sling it is important not to make corrections reflecting the gauges as one normally would, but instead understand exactly what the load is doing beneath you. The attitude indicator reflects rhythmic changes in bank angle from the load tugging the helicopter laterally side to side, as does the ball in the inclinometer. The inclinometer is used to indicate when and how much lateral cyclic input is necessary for a correction, though there is a natural lag. The load will reach its apex prior to the inclinometer, and the pilot must compensate for this natural lag. When the ball starts to swing out of center to the right and is about half way from its apex, the load is almost at its apex to the left, the pilot then uses left lateral cyclic as a correction. The rhythmic oscillations in the attitude indicator and inclinometer reflect the movements of the load, and the average of these movements are the actual orientation of the aircraft.  The pilot learns to mentally average these oscillations in order to control the pitch, roll, and yaw of the aircraft itself.

“An ounce of prevention is worth a pound of cure”, so one learns to make flight control inputs very smoothly so as to not aggravate the load. Turns are initiated slowly, and half standard rate turns are sometimes prudent.

Determining cruise airspeed

Another consideration is determining the target airspeed at which to fly.  This must be greater than Vmini (minimum IFR speed) and less than the loads effective Vne. While the aircraft will have an external load airspeed limitation, this may not be possible if the load is unstable at a lower speed. Many loads cannot be flown at the external load Vne, and the effective Vne must be determined. As the pilot slowly accelerates during takeoff, the load is carefully watched prior to IMC to determine what airspeed above Vmini the load can be flown at. Once that airspeed is determined, it is maintained for the entire flight.

Should the load show signs of instability below Vmini or only slightly above so as to not provide a safe and adequate airspeed window, the takeoff is aborted while still VMC.

One should be sure of a load’s stability and capability at a safe airspeed prior to IMC, and one should only fly known loads in IFR or at night. A known load is one that is similar to one previously flown during the day. The load characteristics are predictable and stable.

Autopilots and external load operations

Autopilots and external loads don’t usually mix, and many Rotorcraft Flight Manuals prohibit autopilot coupling during external load operations. The autopilot can be too abrupt in pitch attitude and roll, particularly when initiating and terminating turns. A pilot can make changes with a more gentle touch; such as slowly entering a half-standard rate turn when necessary. The autopilot can be used for stability augmentation; it just shouldn’t be coupled to the flight director directly controlling the aircraft.

Horizontal and vertical situational awareness

Class B sling loads can be jettisoned, either intentionally or unintentionally. The hook release is typically electric and controlled by the pilot. Under normal operation the load is released once it has been placed gently on the ground; however, in the case of an emergency the pilot may opt to release it in flight. Due to the possibility of the load being released in flight, persons or property are never overflown. This requires horizontal situational awareness; easy enough VFR, but IFR is another matter. Fortunately, the North Slope of Alaska provides assurance due to its desolate nature.

Vertical situational awareness must also be considered, not just for the helicopter but also for the load hanging underneath. With the typical 25 to 50’ line, the altitude of the load isn’t a factor in cruise flight; however, during the instrument approach it must be considered.

The Instrument Approach

As much fun controlling the helicopter and load may be in IFR conditions, eventually we do need to land. For that we need to fly an instrument approach. Let’s stick with the North Slope of Alaska, using the Deadhorse (PASC) ILS 05 as an example, using a little simple math.

A load 5 feet high hanging on a 50 foot line would require a 55 foot adjustment factor to the decision altitude. For the Deadhorse ILS, this means increasing the decision altitude of 267 feet to 322 feet, and ALS conditional altitude of 167 feet to 222 feet. It would also be prudent to include this 55 foot altitude adjustment into your preflight IFR planning.

Final Thoughts

While flying slings IFR is no longer common, the training for IFR slings still occurs. Having the skill and confidence to be able to fly a sling IFR is vital should unforecasted adverse weather be encountered, not unheard of on the Alaskan North Slope where the weather can change quickly. Airports and options are few and far between north of the Brooks Range of Alaska. These skills also translate well and are employed for night sling operations, which are still done on a regular basis.

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