Accident Overview
On August 19, 2020, about 0945 Pacific daylight time, a UH-1H helicopter, registration N711GH, operated by Arrow-Falcon Exporters, Inc., was destroyed in an accident near Coalinga, California. The helicopter was conducting a public use firefighting flight. The pilot, the sole occupant, was fatally injured.
The accident flight was the pilot's first day working on the Hills Fire, which had started four days prior. The pilot took off at 0846, followed by another pilot flying a Bell 212 helicopter for a different operator.
Pilot Communications
After departure, both helicopters flew south to a small lake or reservoir to fill external load buckets. They then proceeded to a predetermined area to drop water on the fire. After releasing water, they would return to the dip site. The accident pilot delivered about two buckets of water to one location and then moved to another location, delivering about five buckets.
The Bell 212 pilot reported that after departing the dip site with a bucket of water, he heard the accident pilot communicate over the air-to-air radio that he felt "abnormal noises and vibrations" and planned to make a precautionary landing. The Bell 212 pilot dumped his water and caught up to the accident helicopter to assist. He remained a few hundred feet behind and above. The accident helicopter was about 1,000 ft above ground level, maneuvering at 60 to 70 kts. The accident pilot then stated that "temps and pressures are good," and a few seconds later said "it's my hydraulics." The Bell 212 pilot advised a right turn toward less mountainous terrain.
The helicopter began a right turn, then banked left while losing airspeed. The Bell 212 pilot noticed the external load bucket still attached and told the accident pilot to release the long line and gain airspeed. The accident pilot declared "Mayday, Mayday, Mayday." The left turn steepened, the helicopter maintained a level pitch attitude, and then made three or four 360° rotations while drifting northeast. The helicopter then pitched nose-low, near vertical, and collided with terrain. A fire erupted immediately.
Wreckage Examination
The helicopter came to rest on a 35° slope, with main wreckage about 25 yards downslope from initial impact. Most of the wreckage was consumed by fire. The tail rotor assembly was intact with no rotational scoring. The wreckage was recovered for further investigation.
The airframe was highly fragmented and mostly consumed by fire. Surviving sections included parts of the tailboom, tail rotor, engine deck, cabin doors, landing skid tubes, one cross tube, and the engine. The main rotor head, blades, stabilizer bar, and upper transmission were lost during recovery.
The cockpit was highly fragmented and fire-damaged. The engine control panel was separated from the center console with switches deformed downward. The caution warning panel sustained fire damage; nine intact bulbs were removed, two exhibiting hot filament stretching. The fuel valve switch was unreliable for determining pre-impact position.
Portions of flight controls were identified, but most were consumed by fire. Main flight control servos were separated from input and output control rods. The upper flight controls were not present for examination. Tail rotor control cables remained within the tailboom.
NTSB Materials Laboratory examined the left lateral, right lateral, and collective hydraulic servos, and an irreversible valve assembly. X-ray and CT scanning identified high density metal particles deep within the irreversible valve assembly. The right lateral servo showed fire exposure, with oxide layer, micro-cracks, and deformation. Ring seals were fractured. Disassembly of the irreversible valve assembly revealed bending deformation on the cover of the sequence valve, and ring seals were fractured and could not be removed. Check valve "A" seat showed wear damage; check valve "B" seat showed no wear. The left lateral servo's piston was completely retracted; it could not be determined if this indicated a left hard-over condition. It could not be determined if any servo functioned normally before impact.
Heat from the post-crash fire caused carbonization and fractures of elastomer seat rings. Foreign particles were found in the hydraulic system, but it is unknown how much was introduced during firefighting.
Engine and Systems Examination
The engine sustained impact damage. Inlet guide vanes and compressor blades were bent opposite rotation direction with leading/trailing edge damage. The centrifugal compressor impeller showed rotational scoring. Metal deposits (aluminum, stainless steel, magnesium) were found on turbine blades, consistent with engine operation at impact. White dust-like material (magnesium oxide) covered the combustion liner interior.
Tail rotor drive shaft segments 1 to 3 were not recovered. Drive shaft segments 4 to 6 were identified. One tail rotor blade showed no damage; the other had chordwise dirt streaks and heat damage.
The cargo hook had separated from its attachment hardware. The final location of the external load bucket is unknown; the witness did not see the bucket released.
Medical and Toxicology Findings
The Fresno County Sheriff-Coroner's Office determined the pilot's cause of death as multiple skeletal and visceral injuries due to blunt impact, with manner of death as accident. No significant natural disease was identified.
Toxicology testing detected ethanol at 0.11 gm/dL in peripheral blood and 0.068 gm/dL in gastric contents. FAA Forensic Sciences Laboratory detected ethanol at 0.082 gm/dL in cavity blood and 0.082 gm/hg in muscle tissue, but not in brain tissue. N-propanol and methanol were detected in cavity blood. Putrefaction was noted. The antidepressant citalopram was detected in blood (5,857 ng/mL) and liver; its active metabolite n-desmethylcitalopram was also detected. The anti-anxiety medication buspirone was detected in blood (1.1 ng/mL) and liver.