#### Author: Markus Lavenson (page 1 of 2)

Whether flying helicopters or airplanes, sometimes it may be necessary to modify a flight plan enroute to incorporate an alternate route, altitude or destination. If plan A isn’t working, relax, there are plenty more letters in the alphabet.

Diligent planning prior to takeoff helps ensure that altering a plan in flight won’t be cause for concern. Whatever change is considered, it must be within the capabilities of the aircraft with regards to the amount of safe fuel onboard. The range of the aircraft, considering the amount of safe fuel and current environmental conditions, is called the radius of range (ROR). The ROR is never static, but constantly changing throughout flight.

Many of us fly aircraft over desolate areas of the West and Alaska, or offshore to oilrigs where refueling locations and helidecks are few and far between. Though helicopters have some advantages over airplanes, range and fuel endurance isn’t usually one of them. Beating the air into submission takes a lot of fuel, with a relatively high fuel consumption to weight ratio as compared to airplanes. On the other hand, while airplanes tend to have more range than helicopters, they are more restricted on where they can land. Both aircraft have their advantages, and all pilots need to continually assess available options which may be affected during flight due to changing weather and wind conditions, aircraft performance and condition, and the amount of safe fuel remaining. Safe fuel is the amount of fuel not including a reserve; the reserve being the greater of what is required by FAA regulation or what the pilot considers necessary.

Many pilots regard fuel planning as a linear calculation, where only the departure and destination points are considered. The formula for point of no return (PNR) is such a calculation that does not consider options off the route of flight. The PNR is a specific point along the route where should the aircraft fly beyond, it will lack sufficient fuel to turn back and safely land at the departure location with a reserve remaining. Below is the formula for PNR in minutes and conversion to PNR in miles.

Safe fuel (minutes) x GS2, divided by GS2 + GS1  = PNR (minutes)

PNR (minutes) x GS1, divided by 60 = PNR (miles)

1. GS2 is the ground speed opposite of the course to be flown.
2. GS1 is the ground speed on the course to be flown.

Using the two formulas one can determine the PNR for a flight in terms of the number of minutes flown and the number of miles flown. Subtract the PNR miles from the total route miles to determine the amount of miles remaining to the destination, which may be more useful when viewing a GPS or FMS. While PNR for a flight is a useful calculation, it is a linear 1-dimensional calculation and we can do much better adding more dimensions to our planning.

Most of the time a flight will have more options available than simply the departure and destination locations, and so we find the old PNR formula and that way of thinking to be insufficient. Let’s add another dimension and consider not just the route of flight, but also the possibility of changing course anytime should changing conditions dictate using the ROR concept.

I recently flew a helicopter from Anchorage to the Leonardo Helicopters factory in Philadelphia, which was more than 3200 nautical miles with 14 fuel stops. ROR flight planning was a critical aspect, especially during the first few days through Alaska and western Canada. However, it would increase the margin of safety for any cross-country flight, regardless of where one is flying.

The ROR is the distance the aircraft is capable of flying at any given point, and is represented by a large circle around the current aircraft position. The radius of that circle is dictated by the amount of safe fuel on board, cruise speed, and winds aloft. Let’s use a heavily loaded AW139 flying at 150 knots only carrying 1.3 hours of safe fuel as an example. In calm winds, the ROR at takeoff would be 195 miles, which is the maximum distance it could fly and still land with a reserve remaining.  During flight as fuel is consumed the ROR will naturally decrease.

chart 1

On this chart, the yellow circle depicts the ROR departing from Burns, Oregon. At this point, the aircraft is just starting to consume fuel and the ROR is at its largest. We can see at takeoff the destination is just within the ROR, indicating a planned landing with just the fuel reserve remaining. As the flight progresses and fuel is consumed the ROR decreases, and there becomes a point a little over halfway where returning to the departure point is no longer an option, corresponding to the PNR. The orange circle is the ROR at 93 nautical miles, the halfway point of the flight. As we near the destination the ROR continues to decrease to the point where many fewer options are available and at a certain point the only course of action is to land at the destination. The red circle is the ROR at 140 nautical miles. There are just four other airports within the ROR at 140 nautical miles and in another 20 nautical miles there won’t be any, other than the destination itself.

In the chart below we have essentially the same ROR chart, but with a 20-knot wind out of the west. As one can see, all the ROR circles offset downwind. This graphically shows that with a strong wind condition one is usually better off turning downwind for an alternate option, as there is more area within the ROR downwind than there is upwind.

chart 2

Let’s add the third dimension to consider: altitude. Note that everything within the ROR may not necessarily be a viable option. It is possible that parts of the area within the ROR are further constrained by high terrain and weather. Maybe a ceiling prevents a climb in VFR to a necessary altitude in order to safely clear a mountain ridge east of course. Or maybe its getting near the end of the day when daylight will be waning and crossing a mountainous area in VFR flight without much illumination isn’t safe. We obviously don’t live in a flat world and must consider altitude.

The last dimension is time, and is considered throughout the flight. A prudent pilot will assess if weather currently reported is better or worse than forecast, and try to get an idea of what the trend is up ahead and near the destination. On this particular flight a pilot would make early and careful assessments as to winds aloft, changing current weather conditions, and amended forecasts along the route of flight and areas inside the ROR. Should one encounter a worse than planned condition, such as a stronger headwind or worse than forecast weather enroute, making a decision to alter the planned flight in the early stages is better than in the later stages. In the early stages more options are available and one can carefully choose the best, whereas in the later stages of the flight options will have dwindled along with fuel. With deteriorating conditions this flight could evolve into a situation supporting the old adage; a superior pilot uses superior judgment to avoid the necessity of using superior skill. As we know, superior judgment for a pilot is using all available information to determine what risk may present in the future, and then determine a course of action to avoid or mitigate that risk.

chart 3

The final chart is an example how a pilot might incorporate terrain issues, forecast weather and NOTAMs into the ROR chart. One can add notes along with the depicted ROR circles. Maybe weather forecast to the west towards Pendleton and Walla Walla indicates marginal VFR conditions. One may consider taking those areas out of the ROR, especially coming from higher terrain where it may not be possible to safely get under a cloud layer. To the east is higher terrain, which may block access in that direction; it is also the windward side of a mountain area, which tends to collect a lot of cloud cover. Also noted is a NOTAM for an airport along the route of flight for fuel out of service, though it could still be used for a safe landing as one of the last options. Airports circled in green highlighter represent good enroute options should a diversion with landing become prudent, such as when facing deteriorating weather or an aircraft problem of some kind.

Of course if things really get bad, let’s call it plan Z, we can usually find a place to just land. Helicopters definitely have an advantage over airplanes for landing off-airport, though I’ve seen some amazing bush pilots in Alaska. Plan Z is certainly better than running out of fuel or flying into dangerous weather, and sometimes, JUST LAND is the best option. During my power line patrol days in the 1980s, I knew many of the farmers along the route from visits during the summer. These farms made for some good alternates during the winter, when I would occasionally land for a welcomed cup of coffee to wait out the odd snowstorm.

The ROR certainly doesn’t provide everything a pilot needs to think about but it does help with a graphic visualization of areas available throughout the flight. Next cross-country flight, get a sectional chart out and make some ROR circles using a highlighter along the route of flight. Use any color and at any increments you desire. Remember to offset the ROR circles downwind, in relation to wind speed and time of flight. For example, a 40-knot wind would have an offset of 40 nautical miles for an hour flight, 60 nautical miles offset for a 1.5-hour flight, and an 80 nautical mile offset for a 2-hour flight.

Once in flight, there isn’t much a pilot can do to alter the aircraft ROR.  Consider how slowing down to a maximum range cruise speed will increase the ROR.  Hopefully, your Rotorcraft Flight Manual will have fuel consumption charts, if not you will have to rely on past experience for fuel consumption rates.

Maybe someday flight planning and moving map apps, such as Foreflight will provide an enhanced ROR map overlay option, but for now a couple of colored pens and a trusty sectional chart will suffice.

In the event of an engine failure, airplanes have a distinct advantage of being able to glide farther than helicopters, hopefully far enough for a safe forced landing.  While helicopters can’t glide as far, they do have the great benefit of being able to land with little to no groundspeed, greatly improving the survivability of those on board. The best of both worlds would be to be able to glide efficiently and then land without any groundspeed. While a helicopter is able touch down with little to no groundspeed, a glide angle of about 18 degrees won’t garner much range. However, there is a technique, not included in the FAA Rotorcraft Flying Handbook, that can be used to extend the range and in some cases help reach a more desirable landing area.

During an autorotation there are many things a pilot can do when too high; turns, slips/skids, or airspeed adjustments. However, when faced with the situation of being too low, there is only one thing a pilot can do.  Extend the autorotation glide.

There are four factors in an autorotation that affect the descent rate: density altitude, gross weight, rotor RPM, and forward airspeed.  While we can’t control density altitude or gross weight (unless jettisoning an external load), we can control rotor RPM and forward airspeed. In a forward flight autorotation one can significantly increase the range by increasing airspeed and lowering rotor RPM, while still complying with the Rotorcraft Flight Manual limitations for that particular helicopter.

Let’s take airspeed first, using the Agusta Westland 139 as an example, referring to the RFM limitations and emergency procedures sections. The AW139 has a minimum autorotational airspeed of 40 knots, a minimum rate of descent autorotational airspeed of 80 knots, and a best range autorotational airspeed of 100 knots. Some helicopters may not have a best range airspeed published, but instead a maximum autorotational airspeed. In any case, one would use the autorotational maximum airspeed or best range airspeed to extend the power-off glide. Note, the minimum rate of descent airspeed also corresponds with the best rate of climb airspeed (Vy), as this is the airspeed where the coefficient of the lift to drag ratio is highest. The farther one deviates from Vy the greater the descent rate. Know that exceeding the maximum or best range autorotation speed can cause rotor RPM decay and put undue stress on the rotor blades, and we certainly don’t want to decay rotor RPM because we want to use it for lift to extend the range in an autorotation.

We have increased speed to the maximum allowable, but are now faced with an increased descent rate as the helicopter is now faster than Vy. However, this can be compensated for by increasing collective and reducing rotor RPM to minimum allowable, which decreases the descent rate.  The AW139 has a power-off rotor RPM limitation of 95-110 percent, not counting transient limitations.  In order to maximize the autorotational range of the AW139, fly at 100 knots and 95 percent RPM. At some point with ample altitude remaining, the pilot would reduce the airspeed to the recommended 80 knots and increase the RPM to the recommended 110 percent. This provides as much energy as possible to the rotor system for landing. Aircraft vary as to how quickly they can recover rotor RPM, and while a low inertia rotor system will recover quicker it will also have less energy during pitch pull before touchdown.

There is really just one reason to fly an autorotation at the maximum airspeed and lower range of rotor RPM, and that is to increase the range of the helicopter. As we increase collective, pitch is increased and the L/D (lift drag ratio) of the rotor system becomes more efficient and more lift is produced.

Next training session, try a couple of extended range autorotations and compare them to the standard ones. Results vary with the type of helicopter, but the difference is very significant in the aircraft I have flown.  ou will likely find the rate of descent at high speed/low RPM to be even less than the rate at Vy/normal RPM. A lower descent rate coupled with a higher airspeed greatly enhances the range, which could make all the difference someday.

We all know it is the pilot’s responsibility to insure the helicopter is flown in accordance to limitations, which in part requires knowing the helicopters takeoff weight. However, due to the versatile nature of helicopters it isn’t always as simple as back in flight school. We may find ourselves picking up a sling load such as a log. How does one weigh a log? A dozen passengers off a ship. Ever try to use a scale on a heaving ship? Or out in the bush of Alaska picking up crew and equipment.,What scale?  One aspect that goes along with flying the ultimate off-road vehicle is that we may find ourselves in places without scales.

An AW139 lifts a daisy chain sling load on the North Slope of Alaska. This helicopter has a load cell and so the pilots were able to monitor and verify the weight of the cargo.

Most helicopters are not flying sling loads nor have a load cell installed, so we need another method of weight verification. Fortunately some performance charts can be used for this purpose. Performance charts are predictive, enabling a pilot to accurately determine variables prior to takeoff and many can be used in a variety of ways depending on which variables are known. The Sikorsky S-92 flight manual makes this an easy process, with the Indicated Torque Required to Hover in Ground Effect chart. One can predict what the indicated torque per engine will be for a specific weight, density altitude and wind condition. In this example, a negative 3,000-foot density altitude with a 10-knot headwind would equal 66 percent per engine torque for a gross weight of 23,000 pounds. For the same density altitude and wind condition, 83 percent per engine torque would indicate the maximum gross weight of 27,700 pounds is being exceeded. Using the chart it’s easy to see that that 1,000 pounds is equivalent to about 3.5 percent per engine torque, for a given density altitude and wind condition.

Using the Indicated Torque Required to Hover in Ground Effect, one can obtain the predicted torque for the S92 at a specific aircraft weight, density altitude and wind condition.

If the aircraft lacks this type of chart, a little m,ore work is necessary. The takeoff and maximum continuous power Hover in Ground Effect charts also provide maximum weights for a range of density altitudes. This gives a start for making your own quick reference chart, and after a couple dozen flights you can add more data points with other power settings. Say you flew 500 lbs under gross weight with a 1000-foot density altitude; simply note the torque in a stable in ground effect hover and enter the torque, density altitude, and weight on your quick reference chart. Over time, you will have created a chart to use as an aid when you are unsure of the aircraft takeoff weight. An external load pilot, without a load cell may opt to use a HOGE (hover out of ground effect) chart instead of a HIGE chart. Experienced pilots with a lot of time-in-type already have a pretty good idea of the power required for specific weights and density altitudes, which is essentially what this quick reference chart provides.

The pilot should also note the cyclic position necessary to maintain a stable position over the ground, providing an indication of the aircraft’s center of gravity. An excessive lateral or longitudinal deviation from a normal position can indicate a CG out of normal range. Wind can also effect the cyclic position, but experience in type will help you learn what a normal cyclic flight control position should be in a variety of conditions. For example, a farther forward and left cyclic position than normal would indicate an aft and right CG, which a left quartering headwind could also cause.

These methods are certainly not a substitute for a proper weight and balance calculation using accurate weights. They are a means of verifying your calculations, particularly when in situations where the weights provided may be in question. It is also a means of understanding the performance of your helicopter better.

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.

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 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.)

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 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 www.joeklineart.com

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.

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.

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.

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.

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.

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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 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.

Imagine being able to create an instrument approach while en-route, and then fly the approach down a minimum of 200 feet and 3/4sm. Not as crazy as it sounds. Here’s why:

IFR helicopters do this regularly, supporting the offshore petroleum industry in the Gulf of Mexico, flying as far as 200 miles offshore to land on ships, drill rigs, spars, and platforms.  All in accordance with Advisory Circular 90-80B: Approval of Offshore Standard Approach Procedures (OSAP), Airborne Radar Approaches (ARA), and Helicopter En Route Descent Areas (HEDA).  The title is certainly a mouthful, and the 58-page document can also be a little daunting. It helps to look at one in action, in this case the popular Copter Delta 30 OSAP, pronounced as “Oh-Sap.”

Before first light, prior to start-up for an IFR flight offshore, which will incorporate an OSAP approach to the destination rig. Photo by Alex Geacintov

The Copter Delta 30 OSAP is one of five charted templates in AC90-80B that a pilot can adapt to almost any location offshore. It requires specific two pilot crew training, GPS, ground mapping capable radar, and radio/radar altimeter. It is a SIAP (special instrument approach procedure), and therefore also requires FAA authorization.

While en-route, destination weather is rechecked via radio or satellite phone. If the destination doesn’t have approved weather reporting, normally required under part 135, some operators have an FAA authorization to use remote reporting stations. Operations Specifications are regulatory and issued by the FAA, with some being more restrictive and some less restrictive than the associated FAR. Think of them as an extension of the FARs for specific operators. In this case the Op Spec is less restrictive, which is a good thing because although there are some AWOSs  offshore, there never seem to be enough.

The OSAP Delta 30

Wind condition at the destination is used to determine the approach course, which must be into the wind. A DWFAP (down wind final approach point) is typically created 7nm downwind from the destination, on the final approach course. The DWFAP can be created anywhere on the final approach course, as long as it is between 5 and 10nm from the destination. Depending on the en-route direction, a course reversal may be necessary in order to establish the helicopter inbound on course at the DWFAP. All this is planned and created while en-route, and then programmed into the Flight Management System or GPS. Radar in ground-mapping mode is used to determine there are no obstacles within .5nm of the final approach course. The final approach course can be adjusted for obstacles, just as long as it is within 10 degrees of the wind.

When 40nm or less from the destination, a cruise clearance is requested from ATC. This allows an immediate descent to MEA, an eventual descent to 900 MSL 20nm out, and a clearance to fly the approach and missed approach, if necessary.

Once established inbound at the DWFAP, at or below 70 knots (ground speed), a descent from 900MSL to 500MSL can be initiated.

If there are no obstacles within .5nm of course, and the radar and GPS are in agreement within .2nm for the destination target, a further descent from 500MSL to 200RA (radio altitude) can be made.

Radio altitude, from a radio or radar altimeter, is the actual height of the aircraft above the surface, in this case the ocean. The radio altimeter is used to determine the height, while the radar is used to identify obstructions. It’s a dynamic environment and just because an approach was clear of obstacles the day before doesn’t mean a drill ship wasn’t repositioned overnight.

At 1.1nm out, a right or left 30-degree turn is made to avoid overflying the destination, hence the name “Delta 30”. The heading change still has the aircraft converging with the destination, with the MAP (missed approach point) being .6nm away. At the MAP, one can proceed visually to land or go missed approach.

An OSAP is a great procedural tool for the trained two-pilot IFR crew in the offshore environment, providing precision approach-like minimums.

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

The rig looms ahead after shooting an OSAP Delta 30 instrument approach.  Photo by Paul Petrone

Fresh coconuts everywhere! We hadn’t had any fresh food in the last couple weeks, unless you count coleslaw; nothing lasts longer at sea than cabbage and carrots. I started up the Bell-Soloy helicopter to begin shuttling crew to a Pacific island atoll. We were going grocery shopping.

An uninhabited Pacific atoll

It was 1988 and we had been at sea almost two months and the holds were far from full. My job was to fly the helicopter in search of tuna, and then help catch them by herding them into the net. We were to fill the Maria Rosana II with about 1,300 tons of tuna. She was a fast 225-foot tuna clipper with a crew of 23, five speedboats, and a helicopter. We used a seine net almost a mile long and 500 feet deep, with one end attached to the skiff and the other to the ship. When setting the net, the skiff was released and the tuna boat would make a huge circle back to the skiff. A cable, which ran through metal rings all along the bottom of the net, was then winched, closing off the bottom of the net. The net was then pulled through a power block until the tuna were packed tight. They were then scooped out and funneled through a chute into a hold for freezing. Simple enough, except tuna are 47 mph fast and lately schools had been hard to find. Holds full or not, we would soon be low on ship fuel and have to return to port. After months of hard work, we could now have a little enjoyment. After all, how many people get to land on uninhabited Pacific atolls?

After shuttling several guys to the island, I shut down the helicopter and started walking around. The birds had never seen humans and were unafraid of us; we had to zigzag to avoid stepping on them. As I walked the oceanside I saw multitudes of fish and some very large and inquisitive moray eels. The lagoon side was full of baby sharks. It was pristine and untouched.

Back at the helicopter, the guys had already accumulated a very large pile of coconuts. The copilot side door had been installed (no dual controls), so we were able to fill that entire side of the cockpit with about 20 coconuts.  I then flew back to the ship, landed and then reached over to pop the door open, watching most the coconuts roll out onto the deck. The mechanic then reached in and got the few remaining stragglers. After many trips we had a few hundred coconuts all over the helideck. The helideck had a metal lip about 4 inches high around the edge and was cambered, which caused the coconuts to roll away from the helicopter. Soon, there was barely enough room to land.

Just before start up and flying coconuts to the boat

Later that day our pleasure was ruined by learning we had to waste a day meeting up with a sister ship to get a needed part. Seems one of the refrigeration solenoid valves was bad. Our mood was quickly restored when some genius figured out gin went really well with coconut milk, likely the helicopter mechanic.

The next day, I flew to the other boat to get the part and while the other pilot cleared the deck, we chatted on the radio.

“Oh by the way, the stabilizer is busted” he said. The stabilizer is a U-shaped hydraulic flume tank near the stern, married to the inside hull of the boat. Tuna clippers are long and sleek; so without a working stabilizer there isn’t much roll stability.

I knew what that meant. But I asked how bad it was anyway.

“Well she is rolling a bit in this swell, just pick your moment and you should be okay.”

“How much is rolling a bit?” I said. He was really getting my attention now.

“Oh, about 30 degree each way, but she’ll settle down once in a while for you to land. No problem, just get the timing right.”

Nearing the boat, I could see they had recently set the net and were laying stern-to in a following swell. This was worst possible position and she was rolling heavily, but I noticed there were pauses. I made an approach, trying to gauge and anticipate the roll. Once over the actual helideck, it was a combination of looking at the horizon and down at the landing area. The deck was moving up and down a manageable 6 feet, but the roll was bad. It was necessary to wait until the deck was fairly level and within the slope limitations of the helicopter, and then get it down fast before the next roll.  As soon as the floats touched down, I quickly bottomed the collective before the next roll. The mechanic rushed out with cargo straps, cinching us to the deck, and I began the two-minute cool down. The ship then took a big roll, which was not a lot of fun; an idling helicopter on a 30-degree slope 35 feet above the ocean. I doubt I could ever get used to that. Soon we shut down and I went into the bridge to look at the inclinometer gauge, which measures the amount of roll. I could hardly believe it, but it was showing regular rolls to 28-degrees both ways; a 56-degree swing.

After the part had been loaded, I climbed back in and started the turbine. After bringing the rpm up to 100 percent, I signaled the mechanic to release the last remaining cargo strap. Waiting for the ship to level, I then applied max power and nosed her over.

After I cleared the ship, I radioed the other pilot. “Hey man, how long has it been like that?”

“It went out at the beginning of the trip about a month and half ago,” he said.

“ Well, if there was a tuna boat helicopter pilot hall of fame I would vote for you.”

“Ha, well the first week is rough, but you get used to it,” he said.

I wasn’t so sure I would get used to it.  Rick was one of our most senior pilots and had been doing this for more than six years and was very good.  I was sure glad our stabilizer was working, and made a mental note to buy some drinks for our chief engineer the next time we hit the beach.

The rest of the trip was uneventful, until we blew up one of the helicopter’s floats with a ¼ stick of dynamite….buts that’s for another blog.

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

Flying to the ship