The NTSB released its preliminary report on a fatal Arizona Department of Public Safety helicopter crash during a law enforcement response near Flagstaff on Febrary 4.
A Bell 407 police helicopter crashed while its crew provided aerial support to officers on the ground who were responding to an active shooter southeast of downtown Flagstaff. The accident occurred around 10:16 p.m. local time, and killed both the pilot and a tactical flight officer, who were the only occupants on board.
Investigators said the crew was working a 24-hour shift, and had rescued hikers earlier that morning, before the evening’s mission to assist law enforcement in Flagstaff.
Law Enforcement Support Mission
Flight tracking data investigators reviewed showed that the police helicopter departed its base in Kingman, Arizona, at about 9:10 p.m. and flew east toward Flagstaff. Once in the area, the crew coordinated with officers on the ground while circling the neighborhood and using onboard infrared equipment to help monitor the suspect’s location.
During the operation, the helicopter maneuvered at relatively low altitude while conducting surveillance over the neighborhood.
At one point during the mission, the pilot climbed and maneuvered to allow another helicopter inbound to Flagstaff Medical Center to pass through the area. After the other aircraft cleared, the Bell 407 returned toward the neighborhood where officers were working the incident.
Police later reported that officers on the ground had exchanged gunfire with the suspect before the helicopter crashed. Authorities said no additional injuries were reported and that the suspect was taken into custody.
Sudden Loss of Control
Video reviewed by investigators showed the helicopter maneuvering north of the neighborhood shortly before the accident while appearing to position for a vantage point over the scene.
At about 10:16 p.m., the tactical flight officer began a radio transmission to officers on the ground. Seconds later, the helicopter entered a rapid right rotation.
Investigators reported that the sudden rotation coincided with an unidentified sound transmitted over the radio, followed by two loud bangs believed to have come from the helicopter itself before it began a rapid descent. During the descent that followed, the tactical flight officer transmitted, “we’re going down.”
The helicopter came to rest on a dirt access road about three nautical miles north of Flagstaff Airport. Investigators said they documented a debris field that extended more than 6,000 feet from the main wreckage.
Early Findings
Investigators said in the report that they discovered that portions of the helicopter’s tailboom and tail rotor assembly separated during the sequence. Investigators documented impact marks and punctures on those components consistent with contact from a main rotor blade.
A review of maintenance records did not identify recent maintenance actions or reported anomalies involving the tailboom or tail rotor assemblies.
Investigators also reported that, although there was an exchange of gunfire on the ground, examination of the wreckage found no evidence of ballistic damage to the helicopter. Review of video and flight data indicated the aircraft’s closest proximity to the suspect at the time shots were fired was about 7,500 feet.
Data recovered from the helicopter’s engine control unit indicated the engine was operating at high power shortly before the sequence began.
Weather observations near the accident site indicated clear conditions with good visibility and light winds at the time.
While the preliminary report of course makes no final conclusions about the crash, the sequence described by investigators seems to point toward a sudden mechanical breakup involving the rotor system and tailboom.
Video, wreckage distribution and damage patterns appear to indicate main rotor contact with the helicopter’s tail structure, which was then accompanied by a rapid loss of structural integrity that would likely have left the crew with little opportunity for recovery. Engine data showing the powerplant still produced power as rotor load disappeared further supports that kind of in-flight failure scenario.
The NTSB stressed that its findings are preliminary, however, and investigators will continue examining the wreckage, systems and recorded data before issuing a final report and probable cause determination.
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