What happened
On January 14, 2025, a Cessna C-208B, registration OB-1870, was conducting a scheduled tourist flight over the Nazca Lines. The aircraft, operated by Compañía Aerodiana S.A.C., departed from Pisco International Airport (SPSO) with two crew members and 12 passengers on board.
Approximately eight minutes into the flight, while in the climb phase and roughly 10 nautical miles from the airport, the crew observed a sudden and simultaneous surge in engine parameters. Values for torque, indicated airspeed (IAS), interturbine temperature (ITT), gas generator speed (Ng), and fuel flow all rapidly increased into the "red arc" limits. The crew attempted to reduce power using the power lever, but the engine failed to respond to the inputs, remaining at maximum operational limits.
In response to the mechanical failure, the crew declared an emergency with Pisco Tower and requested an immediate return to the airport. During the approach, the crew executed the engine shutdown procedure. The aircraft performed a controlled emergency landing on runway 22. There were no injuries to the 14 occupants, and while the engine sustained damage due to exceeding operational limits, the aircraft suffered no significant structural damage.
The investigation
The Peruvian CIAA investigation focused on the mechanical failure of the Pratt & Whitney PT6A-114A engine. Investigators examined the aircraft's maintenance records, confirming that the last scheduled inspection had been completed in accordance with the approved maintenance program and that there were no deferred maintenance items affecting the fuel system.
Technical analysis of the Fuel Control Unit (FCU) was conducted by specialized workshops. The investigation confirmed that while ground operational tests had previously shown acceptable parameters, these static tests failed to replicate the dynamic loads and altitudes encountered during flight, which allowed the incipient failure to remain undetected.
Findings
- The primary cause of the incident was an internal failure of the regulator spring within the engine's Fuel Control Unit (FCU).
- This spring failure led to a loss of fuel flow control and rendered the power lever ineffective, causing the uncommanded surge in engine parameters.
- The crew's appropriate execution of emergency procedures and the engine shutdown procedure prevented further escalation of the incident.
- The aircraft's maintenance history and fuel quality were found to be in compliance with regulatory standards.