What happened
On July 12, 2024, at approximately 1700 Alaska daylight time, a DeHavilland DHC-2T (Beaver), registration N535KT, was involved in an accident near Petersville, Alaska. The aircraft, operated by Rusts Flying Service, was conducting a Part 135 air tour flight within Denali National Park and Preserve.
The flight departed from Talkeetna Airport (TKA) at 1614, intended to fly over the Tokositna Glacier before returning to TKA. While operating over the upper elevations of the glacier, the pilot reported that engine torque indications dropped from 80% to 40% and the propeller ceased producing thrust. The pilot attempted to troubleshoot by cycling the propeller, but torque indications further decreased from 40% to 30%, and the propeller failed to reach the full feather position.
The pilot performed a forced landing into hilly, tree-covered terrain. The engine was shut down and the fuel was turned off approximately 20 to 30 feet above the ground. There were no injuries to the pilot or the eight passengers, but the aircraft sustained substantial damage to the wings and fuselage.
The investigation
Post-accident examination of the wreckage showed that propeller control continuity was intact from the cockpit to the propeller governor. The engine chip detector, reduction gear box filter, oil, and propeller governor screen were all clean. Upon removal of the propeller governor, high-pressure oil was discharged, confirming that oil was being supplied to the governor and hub at the time of impact.
Investigators found that the beta ring micro switch position rod was jammed in the beta ring assembly because the rod had pulled out of the rear bushing and was stuck against it. While the NTSB Materials Lab could not determine if this jam existed prior to the accident, all electrical components, relays, switches, and circuit breakers associated with the beta backup and feather systems functioned as expected. The propeller and overspeed governors were tested and found to be within manufacturer specifications.
Complete disassembly of the engine revealed no buckling damage to the gas generator case or exhaust duct, though one fractured bolt was found at an engine mounting pad. The power turbine shroud housing and disk assembly showed blade tip and path rub. All identified engine damage was consistent with the impact.