Sep 5, 2014
F-35 Head: Delays Coming if Test Planes Grounded Through September
“I need all of [the test airplanes] back to full envelope by the end of this month,” Lt. Gen. Christopher Bogdan said at Wednesday’s ComDef conference in Washington. “Otherwise we will start seeing some delays in future milestones.”
However, any retrofit needed to the F135 engine at the root of the restrictions will be borne by contractor Pratt and & Whitney rather than taxpayers.
The entire F-35 fleet were placed under restrictions following a June 23 fire that heavily damaged an F-35A conventional takeoff-and-landing model at Eglin Air Force Base, Florida. Since then, the small test fleet has had some restrictions relieved, but is still not allowed to operate at full capacity.
While insisting that the Marines remain on track to take the F-35B jump-jet variant operational next summer, Bogdan said there has been a “headwind” of about 30- to 45 days added to test points due to the restrictions. Testing the Navy’s F-35C model at sea is one of the tests affected by potential delays.
The cause of the fire was identified as “excessive” rubbing of a fan blade inside the F135 engine, designed and produced by Pratt. Bogdan went into further detail for the first time on what actually happened to cause the damage.
The issue began three weeks before the fire when a pilot took the aircraft up and executed a two-second maneuver involving adding Gs, roll rate and yaw to the plane at the same time.
Although that move was ““well within the envelope of the airplane,” Bogdan said, those two-seconds led to the engine rubbing against a rubber piece at a much higher rate — and nearly double the temperature — than it was designed to do. In turn, that led to what Bogdan called “microcracks” that went unnoticed until the day of the fire.
“Over the next three weeks of that airplane flying, those microcracks started growing in what we call ‘high cycle fatigue,’” Bogdan explained. “And eventually on the day this happened, that fan-blade system just cracked too much, the whole circular part of that engine — through centrifugal force — stretched out and became a spear; that spear went up through the left aft fuselage of the fuel tank and it was the fuel tank that caused the fire.”
An investigation is still ongoing into the root cause of the issue to discover whether it was a production or design flaw, Bogdan said his team has narrowed down the cause to four sources and should have the results by the end of the month.