History of Flight
On January 11, 2022, at about 1255 eastern standard time, a Eurocopter EC135 P2+, N531LN, was substantially damaged in an accident in Drexel Hill, Pennsylvania. The helicopter was operated by Air Methods Corporation as a Title 14 Code of Federal Regulations Part 135 air ambulance flight. The airline transport pilot sustained serious injuries; the two medical crewmembers and the patient were not injured.
Automatic dependent surveillance-broadcast (ADS-B) data indicated that the helicopter departed Chambersburg Hospital Heliport (PA60) at about 1205, destined for Children’s Hospital of Philadelphia Heliport (9PN2). The track showed cruise at about 3,500 ft mean sea level (msl) before descending and leveling at 2,800 ft msl, then to 1,500 ft msl. At 1253:11, heading and altitude excursions began, with altitudes between 1,700 ft and 1,250 ft msl before the target disappeared at 1253:17.
A witness beneath the flight path reported the helicopter was “very low and louder than normal” with an unfamiliar rotor tone. He observed the helicopter in a nose-down attitude, rotating around its longitudinal axis. A doorbell camera approximately 1 mile from the accident site captured audio and video of the initial descent. A high-pitched whine increased before the helicopter appeared in a near-vertical, nose-down descent; the angle shallowed as it disappeared behind trees. A second witness saw the helicopter “very low…very loud…banked right and left out of control, then appeared to straighten.”
Video clips from open-source media showed the helicopter upright in a steep descent with rapid changes in pitch, roll, and yaw. Another doorbell camera captured the last second of flight as the helicopter appeared level in a slight nose-up attitude before impact, separating the tailboom.
In subsequent interviews, the pilot stated he had no memory of the accident flight. In September 2023, he recalled planning the flight but not the initial incident. He remembered “fighting the aircraft in a dive” and realizing the collective was fully up when the aircraft leveled off but continued descending. He assessed forced landing sites before selecting a touchdown point.
The flight medic reported a loud “bang” heard during the flight, followed by a sharp right bank and roll. The helicopter rolled inverted, and both crewmembers were “pinned to the ceiling.” The helicopter was leveled, the patient secured, and they braced for landing. After landing, the flight nurse evacuated the patient and pilot while the medic shut down both engines.
Personnel Information
The pilot held an airline transport pilot certificate with ratings for airplane multiengine land and rotorcraft-helicopter, with private pilot privileges for airplane single engine land. His most recent second-class FAA medical certificate was issued on August 26, 2021. The operator reported 4,123 total flight hours, including 3,400 hours in helicopters and 185 hours in the accident make and model.
Wreckage and Impact Information
The helicopter initially impacted the ground upright and came to rest on its left side next to a building, heading about 220°. All components were accounted for. Examination of the main rotor, tail rotor, and drive systems revealed no preimpact failures. Both freewheeling units functioned normally. Engines remained installed with impact deformation and thermal damage to exhaust-adjacent components. No anomalous damage was found on first stage compressor blades or power turbine blades.
Flight control system examination, including the automatic flight control system (AFCS), found no preimpact fractures, disconnections, or restrictions. Both collective-mounted engine twist grips were in the normal fly position. Main rotor actuators, fenestron actuator, and hydraulic systems showed no functional anomalies. Black-colored debris in the No. 1 hydraulic filter (pre-filtration) and foreign material at the installation orifice (post-filtration) were identified via spectroscopy as containing carbon and oxygen; similar material was not present elsewhere.
Fault and exceedance data were downloaded from engine data collection units (DCU), cockpit warning unit, vehicle and engine multifunction display (VEMD), caution and advisory display (CAD), and flight control display modules (FCDM). The No. 1 FCDM recorded no faults; No. 2 recorded 11 faults between 48 minutes 7.5 seconds and 48 minutes 10 seconds into the flight, including air data and flight display discrepancies. VEMD data showed a 50-minute flight with 12 failure entries. At 48 minutes 8 seconds, exceedances in mast moment, rotor speed (Nr), and engine power turbine speed (Nf) occurred at 0% engine torque. At 49 minutes 45 seconds, main transmission oil pressure was 1.45 psi. Warning unit data recorded three Nr excursions above 112% and autopilot failure warnings.
DCU data could not be synchronized but showed both engines recorded peak Nf of 126.79% at near-zero torque. Both engine control systems reduced fuel flow to minimum and reverted to manual mode due to Nf overspeeds. In manual mode, the pilot must manipulate the engine twist grip to control fuel flow; if the twist grip remains in the normal fly position, the engine runs at the last known fuel flow rate. The last recorded DCU data, nearly 2 minutes after the overspeed, showed Ng between 23-29%, torque at 0%, and Nf at 0%.
Tests and Research
An EC135 P2+ simulator was used to evaluate helicopter response to various scenarios involving abrupt AFCS disconnection during high-speed cruise flight without hands on controls. Scenarios included disconnection of autopilot upper modes (altitude hold and heading hold) and complete AFCS disengagement via the cyclic-mounted "SAS/AP CUT" button. In scenarios without the SAS/AP CUT button, the helicopter remained stabilized. When the SAS/AP CUT button was used, the helicopter became unstabilized, requiring high pilot workload to regain control. Introducing a dual engine control failure increased pilot workload to land. The most difficult scenario involved dual engine control failure coupled with complete AFCS disconnection via the SAS/AP CUT button.