The pilot's awareness of the helicopter's low fuel status and the near zero indication on the fuel gauge as the flight continued should have given him ample warning of the impending engine failure and provided him with the opportunity to prepare to execute an autorotation. Apparently, that didn't happen.

Simulator flight evaluations conducted during the investigation demonstrated that it was possible to maintain rotor rpm and execute a successful autorotation from low-level cruise flight with touchdown occurring about 25 sec. after engine failure. However, a successful autorotation was only possible if simultaneous flight control inputs of down collective and aft cyclic were made within about 1 to 2 sec. after the engine failure. If these flight control inputs were not promptly made, the result was a rapid decay in rotor rpm and impact with terrain in a nose-down attitude in an average time of 4 to 5 sec. after the simulated engine failure.

The pilot was required to demonstrate competency in performing autorotations during his Part 135 initial and recurrent training. The practice autorotations that Air Methods pilots performed were done at airspeeds of about 80 kt. This was consistent with traditional flight training for autorotations that is typically done at airspeeds below cruise and emphasizes immediate lowering of the collective as the first pilot action in response to a loss of engine power. However, Eurocopter AS350 B1 certification flight test data suggest that following a simulated engine failure at cruise speeds comparable to the accident scenario, the pilot may need to make a substantial aft cyclic input within 1.5 sec. of engine failure to achieve a successful autorotation entry.

The simulator flight evaluations also showed that the helicopter tended to pitch down rapidly following a simulated engine failure at 115 kt., requiring immediate use of aft cyclic to enter the autorotation and avoid an unrecoverable decay in rotor rpm. Pilots might not be able to initiate the appropriate flight control inputs (aggressive aft cyclic, down collective and left antitorque pedal) within such a short period of time unless they have received extensive practice in similar flight conditions. “Thus, the pilot's autorotation training was not representative of an actual engine failure at cruise speed and did not optimally prepare him to respond appropriately to such a scenario,” said the Safety Board.

When the pilot received his training in the Eurocopter AS350 B2, the Air Methods AS350 Flight Training Maneuvers Manual listed “smooth, positive reduction” of the collective to the full down position as the first step in performing a practice autorotation. This was consistent with the emergency procedure in the AS350 B2 RFM and with the general guidance provided by the FAA in the Helicopter Flying Handbook and the Helicopter Instructor's Handbook.

Following the accident, Air Methods changed the guidance on autorotations in its Eurocopter AS350 pilot training program to emphasize the importance of applying simultaneous control inputs when entering an autorotation. “It is imperative that the pilot take immediate action to change to an autorotative attitude; i.e., simultaneously applying aft cyclic, lowering the collective to maintain rotor rpm and trimming the aircraft. Failure to apply aft cyclic while lowering the collective will result in a nose-low attitude; this condition may be unrecoverable at low altitudes.”

The Safety Board says it recognizes that the motions of a helicopter following an engine power loss vary greatly from one make and model helicopter to another and from one flight condition to the next. Therefore, the technique required for safely entering an autorotation will vary, and there is no technique of universal applicability. However, in discussions with experienced helicopter flight instructors and test pilots, NTSB investigators found agreement that simultaneous control inputs, as opposed to only lowering the collective, should be used when entering an autorotation and that the critical task when entering an autorotation is to establish airflow upward through the main rotor system. The instructors and test pilots interviewed reported that the Eurocopter AS350 B2 is not unique in requiring simultaneous application of aft cyclic and down collective to safely enter an autorotation at cruise airspeeds; rather this technique is applicable to many, if not all, helicopters with low-inertia rotor systems.

The Safety Board believes that the additional information about autorotation entries provided by Air Methods to its AS350 pilots would be equally valuable to all pilots flying helicopters with low-inertia rotor systems. Therefore, the Board recommended that the FAA inform pilots of helicopters with low-inertia rotor systems about the circumstances of this accident, particularly emphasizing the findings of the simulator flight evaluations, and advise them of the importance of simultaneously applying aft cyclic and down collective to achieve a successful autorotation entry at cruise airspeeds.

The NTSB's review of the guidance on performing autorotations in the FAA's Helicopter Flying Handbook — the primary source of information on helicopter aerodynamics and flight maneuvers published by the FAA — found that it emphasizes lowering the collective as the initial step in entering an autorotation, does not address the use of simultaneous control inputs in response to an engine failure, and contains minimal information on the entry phase of autorotations. Therefore, the Safety Board recommended that the FAA revise the Helicopter Flying Handbook to include a discussion of the entry phase of autorotations that explains the factors affecting rotor rpm decay and informs pilots that immediate and simultaneous control inputs may be required to enter an autorotation.

Air Methods is now providing all of its Eurocopter AS350 pilots with autorotation training and line-oriented flight training in a full-motion Eurocopter AS350 flight simulator. The NTSB believes that use of a flight simulator addresses the lack of practice representative of an actual engine failure at cruise airspeed in the accident pilot's autorotation training because engine failures in a simulator are representative of an actual engine flameout and can be induced unexpectedly in any flight condition.

This accident highlights the value of using simulators and flight training devices (FTD) for helicopter pilot training.