A US Air Force investigation blames a Lockheed Martin F-35A engine fire last September at Mountain Home AFB, Idaho, on strong tailwinds, according to an accident report released by the service this week.

Winds as high as 30kt blew during as the Pratt & Whitney F135 engine began a start sequence, forcing hot air into the Honeywell integrated power package's inlet. As air temperatures rose inside the IPP -- a mini-engine that supplies electric power and starts the engine -- a series of malfunctions occurred. The lower density of the air produced insufficient torque needed to to the engine, which slowed the rotation of the turbine section.

At the same time, fuel continued to supply the engine at an increasing rate, which spurred an engine fire that burst from the exhaust. The tailwind spread the fire across the aircraft and caused significant damage to a portion of aircraft’s aft section. The fire surrounded the engine’s exhaust nozzle, damaging several nozzle segments as well.

The pilot escaped but sustained minor injuries, including burns on his head, neck, face, and ears, the report states. The service has not yet determined the total costs, but estimates aircraft damages will cost above $17 million.

The report also lays blame on a lack of pilot awareness and training for tailwind conditions during an engine start. A pilot checklist included a warning that strong tailwinds during an engine’s start could cause an IPP failure, but the checklist made no warnings about the tailwind limit. The heavily automated F-35A engine start process also led pilots to believe the aircraft handled most of the start procedures and pilots assumed there were no problems if the dials were green, according to the report.

“Preponderance of evidence shows if there had been an expectation of engine startup problems with a tailwind, the [pilot] may have relied less on aircraft automation, and may have identified an abnormal engine start earlier,” writes USAF Colonel Dale Hetke, who conducted the investigation. “This vague awareness led to inadequate training for engine starts with a tailwind. Training also resulted in complacency and an over-reliance on aircraft automation.”

Source: FlightGlobal.com