Three years and eight failed tests later, the U.S. Navy successfully executed an arrested landing of its F-35 variant fifth-generation fighter this week on the oldest active aircraft carrier in the U.S. fleet.
On Monday, a Lockheed Martin F-35C Lighting II Joint Strike Fighter piloted by Navy test pilot Cmdr. Tony Wilson successfully landed on the flight deck of the U.S.S. Nimitz, marking the fighter’s first successful arrested landing — when a jet is brought to a stop by a tailhook attached to the rear of the aircraft, which snags a wire stretched across a carrier’s deck.
This week’s first successful landing comes about three years after the Navy’s F-35 variant failed eight arrested landing attempts as a result of arresting hook design issues. According to The Aviationist, the distance between the aircraft’s initial tailhook placement and the rear landing wheels was too short, resulting in the arresting cable laying nearly flat on the flight deck by the time the tailhook was in position to intercept it.
Late last week the Pentagon announced the findings of an investigation into an F-35 engine fire earlier this year, which resulted in the third across-the-board grounding of the fleet since the Joint Strike Fighters began undergoing flight tests. (RELATED: Entire F-35 Fleet Grounded Ahead Of July 4 Holiday)
“The engine failure and subsequent fire were the result of micro fractures in one of the three-stage fan sections that compress air before it enters the engine,” the Department of Defense announced in a press release last Friday. “These sections are lined with a polyimide material that is designed to rub against the fan blades to reduce pressure loss.”
In the case of the F-35 in question, the third fan was rubbed “in excess of tolerance” while executing maneuvers weeks before the failure, heating the blades to 1,900 degrees, or 900 more than expected. The rubbing caused fractures in the titanium component of the rotor, which grew over the weeks before the June runway fire.
“That caused that rotor to liberate from the airplane,” Air Force Lt. Gen. Christopher C. Bogdan said. “The fire was caused not by the engine, but by the pieces of the engine that flew out through the aft upper fuselage fuel tank.”
The Pentagon announced two short-term fixes for the problem, including a “burn-in” process that includes flying the aircraft in a specific way in order to break-in the engine “such that where this rubbing occurs has now been burned in, so to speak, and anything else you do with the airplane inside the envelope won’t cause any more rubbing than what it has already seen,” Bogdan said.
In the second fix, engineers “pre-trench” the stator walls, so that “[w]hen we put the fan blade in there, no matter what we do on the airplane G-wise, speed-wise, altitude-wise, it won’t rub anymore,” Bogdan explained.
The general said it will take months to execute fixes on all fielded F-35s, and engine producer Pratt & Whitney has proposed several long-term fixes for future engine production.