F-35 Fire Caused By Tailwind

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The Pratt & Whitney F135 engine of a U.S. Air Force F-35A caught on fire during start, severely damaging the aircraft, due to a tailwind, says the Air Force Incident Investigation Board’s (AIB) report released this week. The pilot of the aircraft received some burns during egress and damage to the aircraft is expected to exceed $17 million. According to the report, “The mishap was caused by a tailwind blowing hot air from either the mishap aircraft’s Integrated Power Pack (IPP) exhaust or the mishap aircraft’s engine exhaust into the IPP inlet. The hot air entering the IPP inlet started a sequence of events ultimately ending in an uncontained engine fire.”

The IPP on the F-35 functions as a combined auxiliary and emergency power unit. Power from the IPP is used to start the main engine. When hot exhaust gases entered the IPP’s inlet, an automatic shutdown of the IPP was triggered. Shutdown of the IPP cut power to the F135’s engine starter, just prior to the engine reaching a self-sustaining speed. The AIB concluded that “since engine combustion had already began, an increasing amount of fuel was delivered to the engine in an effort to increase combustion and overcome the slowing acceleration.” However, since the engine was turning below a self-sustaining speed, the additional fuel, rather than increasing engine speed, resulted in a fire that spread beyond the combustion section of the turbine. The tailwind, in addition to causing in the original IPP fault, then spread the flames across the aircraft.

Based on the local weather at the time of the incident, the tailwind component where the mishap aircraft was parked is estimated to have been 30 knots. There was a note in the pilot checklist stating that “issues could occur” starting with a tailwind, but no maximum tailwind limit during start had been established.

Comments (5)

Great - the most expensive Molotov cocktail in history. What MORONS wrote the engine-start software? If this freshman-class blunder is typical of the software that runs this behind-schedule and over-cost behemoth, then woe betide us all.

Posted by: Tom Yarsley | July 15, 2017 10:24 AM    Report this comment

Sometimes having a good old fashioned manual start method would have avoided this mess. Just goes to show automatic/fadec systems are not infallible. It does look like the IPP fire detection system worked as designed. On the Saab 340 we had an automatic start system that we were trained to use only for emergency in flight restarts. Used a manual start procedure on the ground which forces the crew to monitor the start sequence which avoids issues like this during startup. This procedure was easier on the engine too. Also looks like the manufacturer neglected to do ground testing of starts during tailwind conditions. Hope the pilot recovered from his/her burns ok.

Posted by: matthew wagner | July 15, 2017 4:05 PM    Report this comment

We can fight a air war and win IF it is not a windy day. How quaint.

Posted by: bruce postlethwait | July 15, 2017 5:22 PM    Report this comment

What kind of poorly thought-out FADEC logic would allow this to happen? For shame, software engineers. Wasting millions of taxpayer money.

Posted by: Seth Hensel | July 17, 2017 6:56 AM    Report this comment

Your program is a decade behind schedule and you don't have time to specify "do not start engine in a tailwind"?

Posted by: JAMES MILLER | July 17, 2017 7:02 AM    Report this comment

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