Pilot Debrief

BELL 407 near Charlottesville, VA — 2017-08-12

Final reportERA17FA274
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Date
2017-08-12
Location
Charlottesville, VA, USA
Aircraft
BELL 407
Registration
N31VA
Category
Helicopter
Highest injury
Fatal
Fatalities
2
Phase of flight
Descent

Probable cause

The pilot's loss of helicopter control after entry into vortex ring state, leading to a high rate of descent to the ground with a right spin. Contributing to the accident was the pilot's lack of recent and recurrent training in vortex ring state recognition and recovery.

Contributing factors

Contributing to the accident was the pilot's lack of recent and recurrent training in vortex ring state recognition and recovery.

NTSB narrative

The helicopter pilot and observer were conducting an aerial observation flight. The helicopter had been providing the Virginia State Police (VSP) with a continuous video downlink of the public demonstrations that were occurring in Charlottesville, Virginia, when the flight crew was tasked to provide overwatch for a motorcade. Radar data indicated that the helicopter was flying at an altitude of about 2,200 ft mean sea level (msl) in the area of the motorcade before it began to turn to the right and descend rapidly. Radar data also indicated that, about 30 seconds later, the helicopter was descending through 1,450 ft msl at a groundspeed of 30 knots. Shortly afterward, the helicopter descended below the area of radar coverage, and radar contact was lost. A witness aboard another helicopter observed the accident helicopter descending in an upright position into trees at a high rate of descent. The helicopter impacted the ground and a postcrash fire ensued. Video from a security camera, which was located about 1.2 miles from the accident site captured the helicopter toward the end of the flight and showed that the helicopter was descending vertically at a constant acceleration and with increasing negative vertical speed until ground impact. Photographs of the accident helicopter that were taken by a ground witness revealed that, about the time that the helicopter began its vertical descent, the helicopter was yawing to the right at a rate between 87° and 97° per second. The damage to the main wreckage was consistent with impact forces and the postcrash fire. Hard-body foreign object damage observed on the first-stage compressor blades was consistent with the ingestion of metallic helicopter debris after the helicopter impacted trees and the ground. Thus, the engine was operating at the time of impact. The aft section of the tailboom was found about 100 to 150 feet from the main wreckage site, and pieces of the tail rotor control tube from the midsection of the tailboom were near the main wreckage and the aft section of the tailboom. Signatures of main rotor contact were observed at multiple locations along the aft section of the tailboom. Given the proximity of the aft section of the tailboom to the main wreckage site, the main rotor would likely have contacted the tailboom shortly before ground impact and not during the onset of the right yaw. Although the pedal restrictor control system (PRCS) cam was found in the engaged position, examination of the PRCS found no anomalies consistent with a system malfunction. Therefore, the PRCS cam could have activated during the vertical descent and have limited left pedal forward travel, particularly if the helicopter's nose was lowered during the descent and the resulting airspeed was more than 55 knots (the airspeed at which left pedal travel would be restricted). Regardless, even if the PRCS were engaged, sufficient pedal travel would have been present to maintain heading in a hover out of ground effect. The pilot's autopsy found moderate coronary artery disease without evidence of a previous scar or heart damage. Although the pilot could have been incapacitated by a number of medical conditions, such as a seizure, sudden loss of consciousness, or arrhythmia, that would have left no evidence at autopsy, he did not have a higher risk for such events even with his moderate coronary artery disease. Thus, the pilot's medical condition was not a factor in this accident. Toward the end of the flight, the helicopter's low forward airspeed while descending was consistent with the helicopter entering vortex ring state. As a result, even though power was applied, the helicopter was unable to reduce the descent rate, and it continued descending with an estimated vertical acceleration between 10.5 and 13.5 ft/s2. Anecdotal information indicated that the pilot had knowledge of vortex ring state, but review of the pilot's training records indicated that he had not received any formal recurrent vortex ring state recognition and recovery training during his 16 years with the VSP aviation unit. Also, the VSP aviation unit training manual did not include vortex ring state recognition and recovery in any of the sample lesson plans for initial or recurrent training, and the associated maneuvers were considered to be optional. The helicopter was not equipped with, and was not required to be equipped with, crash-resistant flight recorders. The recovered engine control unit data revealed a sharp increase in torque, from 54% to 104% immediately before the helicopter's descent. Insufficient left pedal input with increasing torque can result in a right yaw that can develop into a spin. The lack of flight recorder data for this accident precluded an evaluation of the pilot's actions before the overtorque and the right yaw. Additionally, the lack of flight recorder data precluded a determination of the pilot's actions during the helicopter's entry into vortex ring state, including any attempt to recover. Last, the available data were insufficient to determine if the right yaw began immediately before or after the helicopter's encounter with the vortex ring state. This accident demonstrates the benefit of crash-resistant flight recorders aboard turbine-powered, nonexperimental, nonrestricted-category aircraft that are not currently required to be so equipped.

Analysis

Primary failure mode
Loss of control
First missed decision gate
Pilot could have recognized and recovered from vortex ring state earlier.

NTSB coding

Evidence available

  • Video
  • Photos
  • 19 docket documents
View NTSB final reportView NTSB docket

Docket documents19

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