Gentlemen –
Thank you for your responses, both pro and con, regarding my emphasis on applying aft cyclic as well as collective down at the first sign of loss of power to the rotor system.
Yes, I call it the best kept secret in helicopters because very few helicopter pilots and instructors realize that not catching the rotor rpm before it drops below the point of no return is the end of the flight. The airplane equivalent is that of losing a wing in flight. Not a good way to fly.
Modern flight schools have been teaching a coordinated entry to training-type autorotations for years. Apply enough aft cyclic to restore the airframe attitude to what is was before the entry was initiated. Perfect. And in the relative sanitary situation that exists during flight instruction, with a CFI monitoring the actions of the student and demonstrating the correct performance of the maneuver, this works well. By sanitary I mean that the flight is conducted within a school atmosphere. All actions are predictable, there is a good place to land if needed, and mistakes can be caught before they turn into an emergency.
This is often not the case in the real world. If you believe that every helicopter pilot is expecting an engine failure at any moment during a flight, you are mistaken. Cyclic Back is dedicated to the hundreds, if not thousands, of helicopter pilots flying all over the world today who have never heard about Cyclic Back and are flying with earned confidence in their aircraft. And then wham. The engine quits without warning. These are the pilots I am addressing, not the freshly groomed perfectly trained pilots graduating from flight schools today.
This forum and the posts regarding the EC135 accident are excellent for the most part. The fact that Dave and his passengers contacted the roof with zero rotor rpm says something. The AAIB has already ruled out a seized main-rotor transmission or equivalent. The engines were not running on impact. So how can the helicopter end up descending with the rotor rpm going down to possibly zero?
Easy. As I said in my earlier post, allowing the rotor rpm to drop below the critical point with no engine power to bring it back into the operating range will cause this to happen every time. No exceptions. And as I said before, there is no recovery from this situation. None.
Notice how all of the flight manuals and training related publications emphasize bottoming the collective at the first sign of an engine failure. They don’t say how much or how rapidly to lower the collective. Just do it, and if the rotor tends to overspeed, pull enough pitch to keep it in the green.
Applying aft cyclic should be done the same way. Just do it. If it was not necessary, then fine. No harm done.
I smiled when I read the posts saying that Cyclic Back was not a good thing to do in a hover, high, low or otherwise. Well, duh. Of course not. Nor is it needed during a low power descent where air is already passing upwards through the rotor disc. It applies directly to the helicopter in powered forward flight, where the pilot is caught completely by surprise with an engine or drive-line failure. Or maybe the pilot is not caught completely by surprise as in the out-of-fuel non-survivable crash of an EMS helicopter in Missouri on August 26, 2011. In any case, if the cyclic is not brought back in time, the rotor rpm continues dropping and can never be stopped or recovered.
Part of our company is our Part 141 flight school in operation since 1980. During that time we have given initial, advanced and recurrency flight training to helicopter pilots of all levels of skill and experience, and we have repeatedly seen high-time professional pilots either do nothing with the cyclic, or worse yet, push it forward, when power was quickly reduced to idle. And the majority of recurrency training has been with law enforcement and military- trained pilots.
Oh, and the noises heard by some witnesses to the crash of the EC135 could have been caused by one or both engines attempting to reignite during the descent.
Finally, this: If you have access to the July 2013 issue of Aviation International News, look for an article about Cyclic Back in the letters to the editor section of the magazine.
Thank you, gentlemen, for allowing me to contribute my thoughts to this perplexing and very unfortunate accident.
Pete Gillies