Accident Overview
On September 29, 2016, about 0600 central daylight time, a Bell 407 helicopter, registration N361SF, impacted terrain following a loss of control while attempting to land at the Comanche County Memorial Hospital Heliport (18OK), Lawton, Oklahoma. The helicopter was owned and operated by Survival Flight under 14 Code of Federal Regulations Part 135 as a positioning flight. Night visual meteorological conditions prevailed, and the flight operated on a company flight plan.
Occupant Injuries
The pilot and two crew members sustained minor injuries. One crew member was seriously injured. The helicopter was substantially damaged.
Accident Sequence
The pilot reported approaching the helipad from the southwest. It was his first landing to this helipad, though he had departed from it the day prior. Due to trees and transmission lines within 40–50 ft of the elevated helipad, the pilot flew a slight right-turning, steep approach. When the helicopter was approximately 125 ft above the pad and 150 ft to the southwest, the pilot commanded left cyclic to stop the right turn. He estimated the helicopter was below 40 knots but above effective transitional lift, with wind off the nose or slightly left, and a stable 500-ft per minute descent. The helicopter did not respond to his control input, and the pilot announced his intention to go-around. He increased left cyclic until it was against his left leg, but the helicopter still did not respond. The pilot lost control, and the helicopter landed hard, colliding with a wall.
Examination
An inspector from the Federal Aviation Administration (FAA) examined the airframe with assistance from a Bell Helicopter technical representative. No preimpact anomalies were discovered with the wreckage.
The engine control unit (ECU) was removed and sent to Triumph in West Hartford, Connecticut. With FAA oversight, data from the unit was downloaded. The data was consistent with the engine producing required power and responding to collective control inputs.
ECU Data
Exceedance information captured by the ECU recorded an exceedance of main rotor speed (Nr) and torque (Q). The unit recorded 10 lines of data with this exceedance containing information consistent with the accident sequence. Prior to the accident, there were two spikes in engine parameters. Without changes in collective inputs, demands of flight control inputs could impact a spike on engine demand.
Pilot Statement
On the NTSB Form 6120, the pilot stated that the helicopter was loaded with three crew members on the right side and a near full fuel load. Up to the accident landing, the helicopter had flown for 6 hours, including 6 approaches and night landings at other hospitals, without incident.