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Amy Wilder

Improper T-bolt installation and maintenance records were <a href="https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193891/pdf">cited by the NTSB</a> as the probable cause in a March 2024 air ambulance accident in Indiana. The Airbus Helicopters BK117C2 sustained substantial damage during a “hard landing” after a critical tail rotor control failure. Two medical crewmembers aboard, as well as the pilot,&nbsp;were not injured in the mishap.
Operating as an air ambulance under Part 135, the helicopter was departing Purdue University Airport (KLAF) in West Lafayette, Indiana, at night when the pilot reported feeling a sudden force on the pedals during a hover taxi. The aircraft began an uncommanded right yaw, and the pilot stated that left pedal input had no effect. Next, the pilot executed an emergency landing.
An examination revealed that the T-bolt connecting the tail rotor pitch change bellcrank to the pitch change slider had separated in flight. The NTSB found that the T-bolt and its attachment bolts had been removed “at the direction of a lead mechanic to facilitate troubleshooting of adjacent components,” after which maintenance personnel temporarily installed the T-bolt attachment bolts “finger-tight” without torquing or safety wiring them as required.
Maintenance records did not include any entry for the T-bolt’s removal or reinstallation, and no verification of its final installation was performed before the aircraft was returned to service. The NTSB concluded that the lack of documentation contributed to the oversight.
One bolt was found on the ramp after the accident, and another had struck the engine bay. The second bolt was found “lodged into a honeycomb panel at the aft-lower area of the fuselage, adjacent to the fuel cell.”

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