CEN18FA078

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.

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.

The New Mexico Office of the Medical Investigator, Albuquerque, New Mexico, performed an autopsy of the pilot. The pilot's cause of death was blunt force trauma with atherosclerotic and hypertensive cardiovascular disease as contributing conditions. The autopsy revealed that the pilot's heart was enlarged, and both ventricles were thickened. Severe coronary artery disease was identified with up to 75% stenosis of the left anterior descending coronary artery and up to 40% stenosis of the left circumflex coronary artery. In addition, there was microscopic evidence of previous ischemia. The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicology testing on specimens of the pilot. Etomidate was detected in heart blood, and 0.032 µg/mL of diphenhydramine was detected in femoral blood. Diphenhydramine was also detected in liver. Review of postaccident treatment records indicated that the pilot was administered etomidate by paramedics following the accident. Diphenhydramine is used for the treatment of the common cold and hay fever. It carries the following Federal Drug Administration warning: may impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery). The therapeutic range for diphenhydramine is 0.0250 to 0.1120 µg/ml. Diphenhydramine can cause marked sedation, altered mood, and impaired cognitive and psychomotor performance. In a driving simulator study, a single 50 mg dose of diphenhydramine impaired driving ability more than a blood alcohol concentration of 0.100 gm/dl. At 1753, the recorded weather at RTN was: Wind 030° at 10 kts; visibility 10 statute miles; sky condition clear; temperature 1° C; dew point -18° C; altimeter 30.26 inches of mercury. According to U.S. Naval Observatory Sun and Moon Data, the end of local civil twilight was 1735 and local moonset was at 1754. The observatory characterized the phase of the moon as "waxing crescent with 0% of the moon's visible disk illuminated." The pilot held a commercial pilot certificate with airplane single-engine land, rotorcraft-helicopter, and instrument helicopter ratings. He held an FAA second-class medical certificate issued on December 7, 2017. The pilot reported on the application for his medical certificate that he had accumulated 6,416 hours of total flight time and 44 hours in the six months before the examination. His medical certificate was issued with the limitation that he must wear corrective lenses for distant, have glasses for near vision. The pilot reported on an insurance questionnaire that he had accumulated 2,065 hours of total flight time in UH-1 helicopters. The pilot rated passenger held a commercial pilot certificate with a rotorcraft-helicopter rating. He held a second-class medical certificate issued on December 11, 2017. The pilot-rated passenger reported on the application for his medical certificate that he had accumulated 3,140 hours of total flight time and 30 hours in the six months before the examination. His medical certificate was issued with the limitations that he must wear corrective lenses, and that the certificate was not valid for any class after December 31, 2018. The pilot-rated passenger reported on an insurance questionnaire that he had accumulated 120 hours of total flight time in UH-1 helicopters. The main wreckage (fuselage) came to rest on a heading about 15° magnetic on a flat mesa about 10.7 nautical miles and 102° from RTN at an elevation about 6,932 ft mean sea level (msl). The mesa consisted mostly of small rocks and prairie grass. The area around the main wreckage was discolored and charred, consistent with a postaccident ground fire. There were no observed sources of ground light or illumination in the vicinity of the accident site. The initial observed point of terrain contact was a parallel pair of ground scars, consistent with the width of the helicopter's skids, which led directly to the main wreckage on a 074° magnetic bearing. The distance from the start of the parallel ground scars to the wreckage was about 474 ft. About 18 ft past the end of the ground scars was a 25-ft-long ground scar consistent with a main rotor blade slap, which ran perpendicular to the path of travel. The entire main rotor came to rest about 60 ft beyond the blade slap signature. The tail rotor and tail rotor gear box were resting nearby. The helicopter's main wreckage was located about 66 ft beyond the main rotor. It came to rest upside down and the entire cabin section between the cockpit and tail boom was destroyed by fire. The right side of the cockpit sustained thermal damage. The cyclic and collective on the left side of the cockpit were in place. The left cockpit side anti-torque pedals were present and connected to their under-deck push-pull tubes. The collective had broken away from its mount. Its twist grip linkage was present and connected. The twist grip's under-deck push-pull tubes moved when the grip's linkage was manipulated by hand. The push-pull tube sections located between the seats were been destroyed. The collective control on the right side of the cockpit was separated from the floor deck. The right cyclic was not located. The right cockpit side's left anti-torque pedal was separated from it mount and the right anti-torque pedal was not located. Their connecting push-pull rod end were fractured into segments consistent with overload. All controls tubes aft of the cockpit were destroyed by fire. Cockpit instruments and avionics exhibited discoloration, charring, and deformation consistent with thermal damage. Two altimeters were located. The altimeter on the left side of instrument panel read 6,760 ft (Kollsman window indicated 30.18). The other altimeter had separated from its instrument panel. The altimeter's 100-ft needle detached from its instrument face. However, the 1,000-ft needle pointed at 6,000 ft (Kollsman window indicated 30.28). The transmission and main rotor mast were present forward of the engine and laying on its right side. The transmission's case had been consumed by fire, revealing the main drive gear and planetary gear train. The main drive gear was intact with no mechanical gear/tooth damage evident. The engine drive/sprag clutch was aligned with the transmission where a fragment of the KaFlex coupling was attached and was consistent in appearance with an overload fracture. Fragments of the KaFlex and torque tube were located in the debris field and displayed signatures consistent with overload fractures. The stationary swashplate was present with one servo connection present. The other two control servo connection horns were destroyed by thermal damage. Three flight control hydraulic servos were located. All aluminum hardware connecting each end of each servo had been melted or destroyed. The rotating swashplate was present with one scissor attached and the other scissor exhibited thermal damage. One main rotor blade damper remained attached to the rotor mast. The other blade damper was located in the debris field near the main rotor assembly. The mast had separated at the rotor head with a circumferential fracture consistent with torsional overload. The engine compressor cases, accessory gearbox housing, and inlet housing were consumed by fire. The output reduction carrier and gear assembly, which attaches to the inlet housing, was intact and recovered as a loose component. Gears within the accessory gearbox were recovered as loose components. There were no penetrations of the combustor plenum. The exhaust tail pipe was disassembled from the engine while on scene to document the second-stage of the power turbine. There were metal spray deposits on the suction side of the second-stage power turbine stator vanes. There was no damage to leading edge of either the second-stage power turbine stator vanes or the second-stage power turbine rotor blades. The