Robinson Helicopter Company R44 II N449MC accident near Alpine, Texas

Probable cause

The pilot’s failure to maintain adequate rotor speed while maneuvering at low altitude, which resulted in a descent from which he was unable to recover. Contributing to the accident was the pilot's decision to conduct the flight at or near the helicopter's performance limit, which precluded recovery of the rotor speed in sufficient time to avoid the accident.

NTSB analysis

The commercial pilot and crewmembers were conducting wildlife surveys and predator control at the time of the accident. The pilot did not have any recollection of the accident sequence. Crewmember statements and GPS data indicated that the pilot was maneuvering the helicopter about 40 ft above ground level when the low rotor speed warning activated. The pilot attempted to regain rotor speed by descending into a small canyon. However, his efforts were unsuccessful, and the helicopter subsequently impacted trees and terrain. A review of GPS data revealed that the pilot had completed a low-speed, 360-degree turn followed by a gradual descending left turn immediately before the impact.

One crewmember reported that the pilot told him that, during the takeoff on the morning flight, the helicopter "wouldn't go" and that the low rotor speed warning came on. A postaccident examination of the helicopter did not reveal any preimpact failures or malfunctions. Postaccident calculations revealed that the helicopter was operated within the gross weight and center-of-gravity limitations. However, the flight was operating at or near the helicopter's out-of-ground effect hover ceiling performance limit.

It is likely that the main rotor speed decayed as the pilot maneuvered the helicopter while it was at or near its performance limit and that the pilot decided to conduct the flight knowing the helicopter was near its performance limit. Insufficient altitude was available to allow the pilot to lower the collective and recover the rotor speed before impact with trees and terrain.

Text from the NTSB. Open the NTSB docket for CEN16LA039 for the full record.