History of Flight
On April 29, 2019, at about 0910 Hawaii-Aleutian standard time, a Robinson R-44 helicopter, registration N808NV, was destroyed in an accident near Kailua, Hawaii. The commercial pilot and two passengers sustained fatal injuries. The flight was conducted under 14 CFR Part 135 as an air tour.
The accident helicopter and another helicopter from the same operator departed Daniel K. Inouye International Airport (HNL) in Honolulu at about 0854 for an island tour. Radar, ADS-B, and FAA ATC data showed the helicopters flying east along the south shore of Oahu, then turning northwest. At 0907:58, the accident pilot reported being over Bellows Air Force Base and requested a northwest transition, which was approved. About 13 seconds later, the second pilot made the same request. About one minute later, the controller asked both helicopters about the weather over Kailua. The second pilot reported that weather was still VFR but becoming harder to see, and that helicopter turned toward the water. About 10 seconds later, the accident pilot, who was further inland approaching Kailua, requested a similar course change, which was approved; both pilots were instructed to maintain flight at or above 600 ft. The accident helicopter began a right turn toward the water at about 108 knots ground speed and acknowledged the altitude assignment. No further transmissions were received.
The accident helicopter continued toward the water for about 0.5 nautical mile, then made a left turn inland over Kailua, with ground speed decreasing from 108 to 104 knots. Speed then decreased to about 100 knots while the helicopter made a gradual right turn parallel to a roadway, continuing to decelerate to about 92 knots. About 0.19 mile from the accident site, at 1,700 ft above ground level (agl), the helicopter entered an abrupt descent; track data ended about 0.11 mile from the site. The last data point indicated the helicopter was at about 1,425 ft agl with a vertical descent rate of 7,360 ft per minute. The second helicopter, about 2.5 miles southeast over water, did not witness the accident and continued uneventfully to HNL.
A witness reported hearing the helicopter overhead, sounding low and loud, but not seeing it due to heavy cloud cover. About 10 seconds later, she heard metal hitting metal, then ripping metal, and saw a piece of main rotor blade spiraling down in an elliptical pattern. Other witnesses reported hearing an odd noise and a loud metallic bang; one saw the helicopter pitch forward, tilt to one side, and enter a nosedive, with a rotor blade detaching. The helicopter impacted a street, and a post-crash fire occurred. A security camera showed overcast skies and captured the sound of the crash, then the helicopter falling through the frame on its side, with one main rotor blade stopped and the tail boom bent at a 90° angle.
Personnel Information
The operator stated that the pilot was hired about 2.5 weeks before the accident. He completed company Part 135 training on April 19, 2019, followed by a week of tour-specific training, and began carrying passengers about three days before the accident. The accident flight was his first of the day.
Meteorological Information
A Pacific Surface Analysis for 0800 indicated a surface trough over the northwestern Hawaiian Islands near the accident site, which can act as a lifting mechanism for clouds and precipitation given sufficient moisture. With trade winds and mountainous terrain, conditions were favorable for rain showers and thunderstorms. The station model near the site showed an east wind of 20 knots.
A Global Data Assimilation System sounding at 0800 indicated a conditionally unstable environment from the surface through 12,500 ft msl, with possible downdraft or outflow winds up to 37 knots. The environment was also favorable for a downdraft, outflow boundary, or gust front from rain showers or thunderstorms, which could cause unexpected changes in wind direction and speed. No additional low-level wind shear or clear-air turbulence was indicated.
Satellite imagery showed a band of cumuliform clouds over the accident site at the time, moving east to west. Weather radar indicated light to moderate intensity echoes above the accident site and along the flight path, with rain shower activity expanding. Radar reflectivity values showed a descending core of 20 to 30 dBZ values from above the site between 0907 and 0915.
Wreckage and Impact Information
The wreckage came to rest in a residential area, with a debris field about 1/4 mile long along a heading of about 009° magnetic. Initial debris included a piece of plexiglass and carpet. Northeast of that, the outboard third of one main rotor blade was found in a fence. The debris path included scattered left-side airframe and cockpit components, cabin items, and the separated main fuel tank about 70 yards south of the main wreckage.
The helicopter came to rest on its left side on a roadway, with a large portion of the forward left fuselage missing. Remaining left-side components showed damage consistent with main rotor blade contact. The left cabin seats were damaged outboard to inboard, and the left corner of the instrument console was bent inward. The aft cabin, main rotor driveshaft and assembly, and engine exhibited postimpact fire damage. The main rotor blades remained attached to the hub, with extensive damage: the blue blade was bent 90° about midspan; the red blade was bent near the hub, with about one-third of the outboard tip fracture-separated. A spanwise dent with equally spaced score marks consistent with windshield bow screws was found on the red blade.
The tail boom remained attached with crush damage forward; horizontal and vertical stabilizers were mostly intact. The tail rotor assembly was relatively undamaged, with limited impact damage.
Flight controls were visually traced and mostly present, with all fractures consistent with overload. The main rotor driveshaft was seized, bent about 20° above the swashplate, with arc-shaped scoring on the hub. Both teeter stops were crushed, the droop stop bolt sheared. The blue blade's afterbody had damage consistent with the left skid toe. The upper sheave of the drivetrain showed rotational scoring, and three V-belts were fracture-separated; one remained intact but unseated. The tail rotor driveshaft had three breaks, one section missing, with no twisting. The vertical firewall had severe impact damage; the cooling fan had rotational scoring and was flattened at 6 o'clock; the oil cooler had a 1-inch-deep indentation from the starter ring gear with grinding and teeth marks. The engine examination revealed no anomalies that would have precluded normal operation.
Additional Information
The helicopter was equipped with a semirigid rotor system. According to the FAA Helicopter Flying Handbook, such systems have two blades rigidly mounted to the hub, which is free to tilt on a teetering hinge. If flapping exceeds design values, the static stop contacts the mast, which must be avoided. Low-G conditions can be catastrophic for two-bladed helicopters; turbulence and severe downdrafts can cause low-G, and combined with high airspeed, may lead to static stop contact. The accident sequence can be rapid, and rotor energy can sever the mast or allow blade strikes.
Robinson Safety Notice SN-32 advises that improper pilot inputs in turbulence increase mast bumping risk, recommending reducing airspeed to 60-70 knots in significant turbulence and using gentle control inputs to avoid overcontrolling.
Medical and Pathological Information
An autopsy of the pilot, performed by the Department of the Medical Examiner, City and County of Honolulu, Hawaii, listed the cause of death as multiple blunt force injuries. Toxicology testing at the FAA Forensic Sciences Laboratory was negative for carbon monoxide, ethanol, and tested-for drugs.