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Thursday, September 1, 2005

Viewpoint

Marty Wright, Chief Flight Instructor, Bell Helicopter

Handling Autorotations

One of Rotor & Wing's recent Tech Talk columns by Shawn Coyle ("The Reality of Turbine Autorotations," April 2005, page 62) was on the mark with its opening sentence: "We all should be practiced enough to know how to recognize and deal with" an actual engine failure.

However, we take exception to the article's statement that practice autorotations are unrealistic and the implication that what is learned from them may not be adequate to cope with the "real thing." The article made a technical case to establish that each phase of dealing with an actual engine failure--the entry, descent, and flare/touchdown--will each have some significant negative helicopter performance differences not previously seen during practice autorotations. It then declared that, if prepared, "instinct takes over and we do what should come naturally."

This could lead helicopter pilots to the unnecessary and incorrect belief that when the "real thing" occurs they may not be able to handle it, even though they've trained diligently and regularly. Also, instinct plays no part doing an autorotation-; we're not born with that innate skill. Dealing with an engine failure is a cognitive process. A pilot learns how to do autorotations.

Over the last 10 years, data shows, there were 418 single-turbine-engine helicopter autorotation mishaps. Of these, 19 had a fatal injury. So of the total actual autorotations, nearly 95.5 percent were successful (if one measures success by not having a fatal injury). This would indicate that pilots are reasonably well prepared to cope with engine failures.

Data shows that actual autorotations are most likely to terminate under far different circumstances than practice touchdown ones. Most actual ones terminate to unprepared surfaces--rough terrain, slopes, water, trees, streets or highways--with the helicopter often left damaged and, worse, not sitting upright.

As Mr. Coyle notes, no one conducts practice autorotations to the sort of hostile terrain where most actual ones terminate. It is obvious why, but this may be the only unrealistic part of well planned and conducted autorotation training.

Regarding the entry, it is true that few pilots will witness even one practice autorotation during an ordinary operational flight. Far fewer will have an actual engine failure. One can expect, and will get, at least one practice autorotation during a typical training or check flight. Consequently, the pilot will undoubtedly be alert for the instructor or check pilot to do that. In training, well-timed and initiated simulated forced landings help develop a positive habit pattern that prepares the pilot to react correctly to an engine failure on every flight, not just on training or check ones.

The correct control inputs for autorotation entry depend primarily on the type of helicopter and the flight regime. Rotor inertia varies among types and has a significant impact on the rate of rotor rpm decay immediately following an engine failure. So, too, does the flight regime. Generally, the slower the speed and the higher the collective setting, the more rapid the decay. But regardless of type, proper training teaches proper pilot input on all controls, not just the collective.

A pilot's response to a simulated forced landing while training may be faster than during an engine failure on an ordinary flight. But training should prepare him or her to understand the consequences of a late response and react quickly enough to an actual engine failure. The key is "quickly enough." It is irrelevant if the pilot's response to an actual engine failure is slower than in training, as long as it is quick enough.

Regarding the descent, if we instrumented a helicopter to allow direct comparison of the sink rate in a practice autorotation (with throttle at flight idle) with an actual engine failure, the engine-out autorotation would probably have a slightly greater sink rate--all other factors being equal. However, in the real world, the difference in sink rates and glides angles between an engine-out and a practice autorotation may be indiscernible, especially to the average pilot's uncalibrated eye (or seat). Also, to which practice autorotation should the engine-out one be compared? The practice one in Toluca, Mexico at 8,500 ft. msl on a calm, 32C day or the one in Vancouver B.C. at 10 ft. msl on a windy, 0C day? It may well be that an engine-out autorotation descent rate under favorable conditions may not be as rapid as a practice one under much more unfavorable conditions.

Bell's flight instructors have witnessed actual engine failures and participated in thousands of practice autorotations. They have a pretty good eye for what a practice one looks like. Not surprisingly, they report there was no discernible descent-rate difference between their actual and practice ones. Even if there was, it wasn't relevant to a successful outcome.

In his many years of instructing, former Bell Chief Flight Instructor Gary Young says, he's done about 50 successful engine-out autorotations and their descent rates were not noticeably different from practice ones. His experience is that the Bell 206B engine-out autorotation descent rate is the same as in a practice one, but with the engine shut down the pilot's fear seems to increase the descent rate. With the recognition that there is no go-around mode, that this is the real thing, it may be only the perceived sink rate that increases. He says every autorotation is unique. On a training flight, the entry point may be different for each autorotation, since each may be initiated during a different phase of flight, speed and altitude. Weather conditions can change, and autorotations--actual or practice--will differ significantly with changes in density altitude and wind.

The point to remember is that every autorotation must be handled for what it is, especially in regard to the particular type of helicopter, the weather, terrain below, etc. It really doesn't matter if or how an actual autorotation differs from a practice one. What matters most is how well the pilot responds to that specific situation, and here is where training will make all the difference.

On the flare/touchdown, we did a non-scientific survey of dozens of pilots training at Bell and our flight instructors. In face-to-face interviews with pilots who'd had actual engine failures in various types of single-engine helicopters and considerable experience on practice touchdown autorotations, the consensus was that they did not notice an appreciable difference in the sink rate, flare, or touchdown between actual engine-out and practice touchdown autorotations. There might have been a difference--for instance, less energy in the engine-out condition to sustain rotor rpm and cushion the touchdown--but each case terminated in a successful autorotation. Each helicopter type has its own rotor rpm characteristics during the flare and collective cushioning. The pilot must learn these so they can be managed effectively.

Universally, practice autorotations are done by reducing engine power and lowering collective to begin the descent--sometimes with maneuvering turns toward a selected area. Some are to touchdown; others terminate with power in a hover. Every pilot should know how to do both. Training with either can be effective, but precision touchdown autorotations help build a pilot's confidence.

Another important element in successful autorotation training is the maneuvering to reach a selected area. If the area can be reached consistently, with sufficient rotor rpm and air/ground speed and descent rate under control at the point when the pilot begins to pull the collective for cushioning, the autorotation--real or practice--will very likely be successful. If you can get to your intended point of touchdown under control, the last 3 ft. shouldn't be fatal. Terminations must involve dangerous uncertainties. You may not be able to avoid hostile terrain such as trees, severe slopes, or frigid water, for instance. But hitting the ground with high air/ground speed and descent rate won't be among those dangers.

It may well be true that practice touchdown autorotations do not replicate the "real thing," and we must accept those elements that are not realistic. Proper training teaches a pilot to recognize the reality of the moment and respond appropriately to those circumstances. It teaches how to use the variables of airspeed, rotor rpm, and maneuvering to make the aircraft do what it is capable of in those circumstances. Successful execution of an autorotation depends on the pilot's ability to develop an enhanced set of skills. With sufficient practice and repetition, those skills will allow him to master the helicopter's idiosyncrasies, characteristics, and performance. This requires a pilot to be alert, initiate the proper control inputs, quickly evaluate what the aircraft is capable of doing, select a landing area from those available, and maneuver to reach it.

It is absolutely essential for a pilot to learn the helicopter's capabilities and limits, as well as his own. This is done through training. Complementary to learning essential stick-and rudder skills is an equally important element - mental preparedness. Proper training goes far beyond the essential stick-and-rudder stage.

Perhaps the most difficult stage of training is correlation--developing the ability to assess the situation (which quite often must be done very quickly), decide what to do, and then do it. This is a cognitive process that requires that every action be predicated on a thoughtful decision. Proper and frequent training is crucial to this process because it allows a pilot to develop his manual skills to the point that his actions will require little thinking and appear to be reflexive. This reflex frees him for a split second from being required to think about how to do an autorotation and think about where he needs to go and what to do to get there.

We at the Bell Training Academy encourage a pilot to visualize what can happen, anticipate possible difficulties, develop prepackaged decisions and foresee a need for assertiveness.

If these elements of mental preparedness are folded into the entire training experience, a pilot will be far better prepared to handle whatever comes along - including that actual engine failure.

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