Bell UH-1H N658H accident near Raton, New Mexico

Probable cause

The pilot's failure to maintain adequate altitude above mountainous terrain during cruise flight in dark night conditions, which resulted in controlled flight into terrain.

NTSB analysis

The commercial pilot, a pilot rated passenger and four passengers departed in the helicopter on a cross-country flight in dark night visual meteorological conditions. According to the sole surviving passenger, the flight proceeded normally until it impacted the ground in level flight and came to rest inverted.

The pilot initially survived the accident but succumbed to his injuries en route to the hospital. A witness who spoke to the pilot before he was transported from the accident site reported that the pilot said that he had flown into terrain.

Overhead imagery revealed that the area surrounding the accident site comprised unpopulated ranchland grass and sparse, low brush. The imagery showed a reduced amount of visual terrain features in the area of the accident site during night conditions and there were no sources of ground lighting or illumination in the vicinity. The pilot's familiarity with the route of flight could not be determined.

The wreckage was located on a nearly-level mesa that rose about 100 ft above the surrounding mountainous terrain. A postaccident examination did not reveal any preimpact anomalies that would have precluded normal operation of the helicopter, and ground scars at the site were consistent with impact in a level attitude.

Toxicology testing indicated a therapeutic level of diphenhydramine in the pilot's blood at the time of the accident, which likely impaired him to some degree; however, it could not be determined if psychomotor slowing from the diphenhydramine contributed to his inability to recognize and/or avoid the terrain.

FAA Advisory Circular (AC) 61-134, General Aviation Controlled Flight into Terrain Awareness, defines controlled flight into terrain (CFIT) as when an airworthy aircraft is flown, under the control of a qualified pilot, into terrain (water or obstacles) with inadequate awareness on the part of the pilot of the impending collision. Professional aviation articles on CFIT state that during night conditions where the height above terrain may be misperceived by a pilot, controlled flight into terrain can occur, even to experienced pilots.

Given the lack of mechanical anomalies and the level impact attitude of the helicopter, it is likely that the pilot failed to maintain adequate altitude during cruise flight and subsequently impacted rising terrain.

Text from the NTSB. Open the NTSB docket for CEN18FA078 for the full record.