History of Flight
On May 2, 2020, at about 0203 central daylight time, an MD 369E helicopter, registration N8375F, was destroyed in an accident near Houston, Texas. The pilot sustained serious injuries, and the tactical flight officer sustained fatal injuries. The flight was conducted as a public aircraft operation under 14 CFR Part 91.
The pilot reported completing a preflight inspection, review of maintenance records, weather check, and safety assessment with no anomalies. The helicopter departed from William P. Hobby Airport at about 0104 for a patrol flight. The pilot's normal procedure was to orbit scenes to the right to provide the tactical flight officer with optimal views. The helicopter completed several orbits over scenes before approaching the accident location. During the second orbit, the helicopter began an uncommanded rotation to the right. The pilot felt a strong vibration in the controls just before the rotation. He performed the emergency procedure for loss of tail rotor, lowering the collective and pushing the cyclic forward to gain airspeed. The helicopter continued spinning violently, and he reduced power while wearing night vision goggles and searching for a landing area.
ADS-B data showed the helicopter slowing to 10-60 knots groundspeed and descending to 600 ft altitude. At 0203:20, it began a tight right turn, accelerating from 10 to 30 knots, then slowing. The turn tightened until 0203:39, followed by 5 seconds of straight flight. A witness video showed the helicopter spinning from 0203:35 to 0203:44 before impacting an unoccupied building and terrain.
Wreckage and Impact Information
The helicopter came to rest on its left side at the base of a building. It initially struck the building's roof and fell to the ground. The wreckage was compact with no significant debris trail and no postcrash fire. All five main rotor blades were present. The left skid was separated; the right skid remained attached. A longitudinal tear was along the fuselage underside. The tailboom stayed attached to the fuselage, but the empennage separated and came to rest near the engine bay. The tail rotor gearbox and blades remained attached. Postaccident examination showed no preimpact failure of structure, main rotor, tail rotor, flight controls, or engine. The fractured tail rotor driveshaft was examined; the fracture was perpendicular to the shaft axis with features consistent with torsional overstress with some bending.
Additional Information
The helicopter was not equipped with a cockpit voice recorder or flight data recorder, nor was it required to be. It had a Churchill navigation system for recording video and GPS data. The last four videos were examined; no relevant information was found. The last frame was recorded about 35 minutes before the accident.
Medical and Pathological Information
Toxicology testing identified ketamine and its metabolite norketamine in the tactical flight officer's femoral blood. Medical records indicated ketamine was administered during attempted resuscitation after the accident.
Survival Aspects
Both crewmembers used three-point restraints. The pilot suffered serious compression spinal injuries and blunt force trauma to the abdomen. The tactical flight officer's cause of death was multiple blunt force trauma, primarily to the abdomen. Both wore flight helmets, but it was unclear if the helmets reduced head injuries.
Tests and Research
The NTSB conducted an aircraft performance study using ADS-B data and weather observations. The flight lasted about 1 hour, with altitude between 400-700 ft MSL and groundspeed 20-130 knots. The witness video showed a yaw rate increasing from 146° to 178° per second to the right, opposite main rotor rotation. The start of the yaw could not be determined. The study considered loss of tail rotor effectiveness and vortex ring state but found them not consistent with conditions. The helicopter was in slow flight below translational lift, where anti-torque requirements change. The increased anti-torque requirement and right rolling moment from accelerating may have contributed to the uncommanded right yaw, but the exact reason could not be determined.