The first multi-ship flight with all three F-35 variants on Nov.19. The US Air Force general in charge of the Joint Strike Fighter program is warning that there is a danger of missing deadlines if his test fleet of aircraft are not flying regularly by the end of September. (Lockheed Martin)
WASHINGTON — The head of the F-35 Joint Strike Fighter program is warning that there is a real danger of missing deadlines if his test fleet of aircraft are not flying regularly by the end of 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.
“Can we make some of that [time] up? Yeah I think we can,” Bogdan said. “But we have to get all of those airplanes up and flying again.”
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.
He also noted that while no microcracks were discovered in other jets, there were marks that indicate potentially similar, if lesser, issues.
Pratt covering retrofits
That leaves the question of how to make sure this problem doesn’t crop up again. Bogdan laid out how his office is moving forward with potential retrofits to the engine.
The first step involves taking a new engine and slowly working it through its paces to get it through the “burn in” phase. Bogdan indicated that testing would begin in the next two weeks, and if that two-sortie process works, it can be replicated for the test fleet.
The second step is more dramatic, requiring a redesign of the F135 to include what Bogdan described as a “pre-dug-in trench” into the fan section to separate the rubber and the fan blade in that part of the engine.
Gen. Mark Welsh, the Air Force Chief of Staff, told Defense News in August that a redesign could be coming for the engine, but Bogdan revealed that they intend to develop a prototype engine for that potential solution.
For fielded airplanes, the Air Force could replace the fan section with the new, pre-trenched fan section in the engines — a relatively painless procedure that could be done in depot.
Pratt & Whitney has agreed to cover the costs of the retrofit engines for the F-35 fleet, a move praised by Bogdan.
“I will tell you that Pratt & Whitney’s reaction to this problem, from my opinion, has been very good. They clearly recognize this is a problem they need to solve,” Bogdan said. “Pratt has said whatever the cost of retrofitting that 156 airplanes is, ‘that will be ours to bear.’”
The general also indicated that the cost for retrofit will not be “very great,” but declined to offer a general cost estimate.
He did, however, indicate that an agreement is close between the government and Pratt that would get engine low-rate initial production lots seven and eight on contract.
“We’re pretty darn close on LRIP-7 and -8,” he said, “but I think the enterprise would expect me to have a root cause and know where I’m going with the next 3,000 engines before I even attempt to buy the next 100.”
A spokesperson for Pratt declined to comment on negotiations with the joint program office.
Bogdan told reporters after his speech that the issue did not have anything to do with a recently disclosed supplier issue with Pratt & Whitney.
In May, the engine company discovered what it called “conflicting documentation” about the origin of titanium used in the F-35 engine, supplied from a firm called A&P Alloys. That led to the company to pause deliveries of its F135 engine while it investigated the issue.
While Pratt has since determined that the titanium in the existing engines does not pose a flight risk, it purged its supply of titanium and opened up a lawsuit against A&P, as well as alerting federal authorities of the issue.
“Pratt & Whitney and Pratt & Whitney Canada are treating this matter very seriously,” a statement on parent company United Technologies Corps website reads. “The sub-tier supplier, A&P Alloys, has been eliminated from our supply chain, and we are no longer accepting parts made from material provided by this company.”
In a statement to Bloomberg News, an attorney for A&P called Pratt’s charges “blatantly unfair.”
The part of the engine that would have used the titanium was “absolutely” different from the part of the engine that caused the fire, Bogdan said, stating clearly that it was an unrelated issue.
“From our perspective, Pratt did everything that they were supposed to do right,” Bogdan said. “We have a problem with A&P Alloy now.”
Asked for further comment, the general said “[The Office of Special Investigations] and the Defense Criminal Investigation Service have an ongoing investigation, and I can’t comment on those results.”