NTSB issues Final Report into Air Methods accident

On 22 January 2022, an Airbus EC135 P2+ air ambulance, N531LN (LifeNet 81), of Air Methods Corporation, crashed in Drexel Hill, Pennsylvania. As a result of the accident, the pilot was seriously injured; the two medical personnel and the patient (a child under the age of five) onboard escaped injury. The US National Transportation Safety Board (NTSB) has now published its analysis and Final Report into the accident.

The report states: “Flight track data from the helicopter air ambulance flight indicated that, while in cruise flight at an altitude of about 1,500ft mean sea level (msl), the helicopter departed normal cruise flight with an abrupt increase in altitude, followed by a dive. The recovered data from various sources onboard the helicopter did not contain information as to whether the helicopter rolled inverted during this altitude excursion, as recalled by the crewmembers. Surveillance video showed the helicopter in a near-vertical, nose-down, spiraling descent. The pilot arrested the rotation and recovered the helicopter from the dive, but was unable to climb or hover due to insufficient engine power, thereby resulting in a hard landing to a city street and substantial damage to the helicopter. Examination of the helicopter revealed no evidence of malfunction that would result in an abrupt departure from cruise flight.”

According to the NTSB report, because of the limited control authority of the stability augmentation system (SAS) actuators, it is “unlikely that a malfunction of a SAS actuator would have resulted in an inflight upset before the pilot could react to the malfunction”. “Additionally,” continues the NTSB, “a malfunction of a trim actuator would not result in an inflight upset as the pilot would notice an attitude deviation before the trim actuator, whose rate of movement is limited by design, would be able to move the helicopter into an unusual attitude.”

Thankfully, both Pratt & Whitney 206B2 engines did as they were designed to do. “Data indicated that a main rotor system overspeed, which likely occurred during the dive maneuver, resulted in the overspeed of both engine power turbines due to the sudden reduction in load from the main rotor. As a result of the power turbine overspeed, both engine control systems, independent of each other, functioned as designed and reverted to manual mode while at a minimum fuel flow rate. Both engines continued to run at low power without automatic governing, resulting in insufficient power to continue normal flight as the engine twist grips remained in the normal fly position for the duration of the flight.”

In an interview with the operator in September 2023, the pilot stated: “I have no recollection of the initial incident. I remember being on the controls and fighting the aircraft in a dive… I realized the collective was fully up when the aircraft finally leveled off but the aircraft was still descending.” The pilot described assessing and rejecting multiple forced landing sites before selecting the point of touchdown. He said: “Since I didn’t think I had any collective left, I pointed towards the landing area and pulled aft cyclic during landing. This all happened in 15 seconds or less.”

Probable cause and findings

The NTSB determined the probable cause(s) of the accident to be an in-flight attitude upset for undetermined reasons that resulted in a rotor system overspeed, a reduction of power from both engines, and a subsequent hard landing.