History of Flight
On August 12, 2017, at approximately 1649 Eastern Daylight Time, a Bell 407 helicopter (N31VA) was destroyed in an accident in Charlottesville, Virginia. The helicopter was operated by the Virginia State Police for a public aerial observation flight, providing continuous video downlink of demonstrations to the command center. The helicopter departed Charlottesville Albemarle Airport around 1600 and arrived over the demonstration area at 1604. At 1642, the crew was tasked to provide overwatch for the Governor of Virginia's motorcade. At 1643, the crew reported heading directly to the motorcade, about 30 seconds away.
Radar data from the Federal Aviation Administration indicated that at 1648 the helicopter was at 2,200 feet mean sea level, traveling north-northwest before turning right and descending rapidly. By 1648:30, it was descending at 6,800 feet per minute through 1,450 feet msl at 30 knots groundspeed, after which radar contact was lost. A crewmember from a Fairfax County Police Department helicopter observed the accident helicopter descending upright into trees at a high rate, followed by debris. The FCPD pilot landed near the site and attempted to assist, but found heavy black smoke and fire.
Witnesses reported that after initially hovering, the helicopter entered a rolling oscillation, began spinning about its vertical axis, and descended in a 45-degree nose-down attitude while spinning. Security camera video captured a vertical descent with increasing speed, and photographs showed clockwise rotation.
Personnel Information
The pilot had been employed by the Virginia State Police aviation unit since 1999 and became unit commander in December 2012. The observer had been employed since July 2017.
Aircraft Information
The Bell 407 was configured with single main controls at the pilot station and locked pedals at the copilot station. The turbine engine featured a full authority digital engine control (FADEC) system. The helicopter also had an airspeed-actuated pedal restrictor control system (PRCS) that limits left pedal travel at higher airspeeds. Above 55 knots indicated airspeed, the PRCS engages, reducing left pedal travel by 25%; it disengages below 50 knots.
Meteorological Information
A high-resolution rapid refresh model for the accident site indicated light and variable winds at 3 knots, clear skies, and no significant turbulence or wind shear.
Wreckage and Impact Information
The main wreckage came to rest upright on a heading of 333 degrees in wooded terrain near a residence. It consisted of the fuselage, main rotor system, and engine, with damage consistent with tree and ground impact and thermal damage from postcrash fire. The aft tailboom section, including the tail rotor gearbox, was found 40 feet up in a tree about 100 to 150 feet away. Debris field extended 300 feet. Main rotor blades were attached; one blade's pitch horn lug was fractured due to overload and thermal damage. The PRCS cam was found in the engaged position, and the emergency release cable was thermally damaged but unbroken. Functional testing of the PRCS unit confirmed normal operation.
Medical and Pathological Information
Autopsies of the pilot and observer were performed. The pilot's cause of death was blunt force injuries to the head, torso, and extremities; the observer's cause was blunt force injuries to the head and torso. The pilot had moderate coronary artery disease with 60% stenosis of the left anterior descending artery. Toxicology testing for the pilot was negative for carbon monoxide, ethanol, and all drugs. The observer's urine tested positive for naproxen, a non-narcotic analgesic; carbon monoxide and ethanol were not detected.
Tests and Research
A performance study used data from the ECU, radar, and ADS-B. The helicopter left downtown Charlottesville around 1644, reaching speeds over 100 knots early, then varying between 5 and 80 knots. ADS-B data showed climbing and slowing airspeed; the descent began at 1648:18. ECU data indicated torque increased from 54% to 104% just before descent, and collective position decreased then increased while altitude continued to fall. Video analysis showed a vertical acceleration of 12 ft/s², and photographs indicated a yaw rate of at least 92 degrees per second clockwise. After 1648:16, the helicopter's low forward speed placed it in conditions conducive to vortex ring state, where increased collective did not arrest descent. Left roll of 30-57 degrees was observed during the descent.
Calculations by Bell determined that with the PRCS engaged, the left pedal margin for hover out of ground effect allowed a tail rotor blade pitch angle of 17 degrees, compared to 25 degrees without engagement.