F-35 Engine Problems Could Impact Marine Corps IOC (UPDATED)

The F-35 joint program office is closer to choosing a permanent fix for engine problems that resulted in the grounding of the fleet in June. However, delays to the test program are putting pressure on the Marine Corps’ ability to meet its initial operational capability scheduled for July 1.

"The engine problem put us behind about 45 days of flight testing,” Air Force Lt. Gen. Christopher Bogdan, head of the F-35 Joint Program Office, told reporters Oct. 30. 

The flight testing necessary to introduce the Marine Corps' variant was scheduled to wrap up Dec. 10. Bogdan projects it will be completed by Jan. 30. That testing is vital to collecting enough data so that the military can clear the aircraft for operations within its full flight envelope. The goal is still to meet the July 1 commitment, Bogdan stressed.

“There’s no way in the world we’re missing that by months. It’s not going to happen,” he said. “We’re talking weeks here. … And that’s good for this program, a program that has been years late on stuff.”

He added, “But if I don’t make it, I’ll apologize.”

Pratt & Whitney — manufacturer of the joint strike fighter’s F135 engine — has presented five potential permanent fixes for the “hard rubbing” of components that ignited a fire during the June incident. By the end of December, Bogdan hopes to have determined what option or combination of options the JPO will select.

“Probably towards the end of 2015, we will start producing engines with the [permanent] fix and then go back and retrofit any of the produced engines that are not in airplanes yet,” he said.

Results of the military’s root cause analysis confirmed that the problem originated with components in the third stage rotor fan section — namely the stator and the polymide seal it comes into contact with. Until a trench forms naturally because of repeated contact, Pratt & Whitney expected some rubbing between those components. However, the excessive rubbing caused temperatures almost double of what was expected.

The heat created micro fractures that propagated and ultimately caused the rotor “to liberate from the airplane,” 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.”

One of the long-term solutions is to change the polymide material to a similar material that can withstand heat above 1900 degrees, he said. Another option is to coat the titanium blade that hits the polymide with a material that makes it heat resistant to those temperatures.

Pratt has also suggested installing a polymide material with a trench already built into it.           

There are also two short-term solutions that have been validated by the military, Bogdan said.  The “burn in” method involves flying two 1-hour sorties with an F-35 equipped with a fairly new engine.

By executing a series of controlled maneuvers, the pilot can gradually form in a trench without causing components to overheat.

The program office has successfully tested that approach on four Air Force test planes, he said.

The second method “pre-trenches” a canal in the polyimide material, so that components will not rub together during operations. That solution has been validated on AF2 and AF4 test planes, Bogdan said.

“As it turns out, that solution works very, very well,” he said. “We inspected the engine and we saw no signs whatsoever of any rubbing at all … which leads us to believe that we can fly through the full envelope of the airplane and not have any of that heating anymore.”

By December, all 19 test airplanes will have undergone either the “rub in” or “pre-trenching” method and can return to normal testing under their full flight envelope, he said.

“The minute we get the okay from the air worthiness authorities on either or both of those solutions, we will start to implement them on the fielded jets,” he added. “It will take a while for us to get through all of the fielded airplanes. I would expect months from now.”

The reason why the JPO needed two methods is because the “pre-trenched” method requires fabrication of a new stator. “Right now we’re only producing one [set] of those per week,” he said, but the program office is trying to accelerate the production of that component.

“If we just went with that method alone, it would take quite a while to replace all the engine fan sections,” he said. “With the rub-in procedure, we can start getting to the same result by flying those airplanes.”

Pratt & Whitney will pay to fix engines on fielded jets and will cover production costs caused by a change in material or procedure, he said.

Despite the engine problems, Pratt & Whitney and the program office reached a agreement today for the 8th batch of low rate initial production engines. The contract is valued at $793 million for 48 engines, bringing the total award to $1.05 billion. From LRIP 7 to LRIP 8, engine cost has decreased by 4.5 percent, Bogdan said.

Lockheed Martin and the JPO reached a similar agreement earlier this week for 43 F-35 airframes.

“The LRIP 8 contract procures 29 U.S. aircraft including 19 F-35As, six F-35Bs and four F-35Cs,” stated a news release from the program office. “It also provides for the production of the first two F-35As for Israel, the first four F-35As for Japan along with two F-35As for Norway and two F-35As for Italy.  The United Kingdom will receive four F-35Bs.”  
The joint program office plans on negotiating contracts for LRIP 9 and 10 at the same time for both the airframe and engine, Bogdan said. He expects an agreement to be reached next fall.

“This allows us to realize the dream that I had two year ago when I took this program over of finally being able to award a contract in the same year that Congress authorized me the money to do so,” he said. “We have not been able to do that ever on this program.”
In the request for proposals for LRIP 11, the JPO will ask Lockheed to do a block buy for partner nations and foreign nations that commit to buy “a substantial number of airplanes.”

“That gives the supply chain an opportunity to now invest in cost savings because now they have at least three years of production instead of year by year,” he said. “That is going to result in savings for our partners.”

Nations that participate in the block buy would pay even less than the United States, Bogdan said. “That’s just simply acquisition economics, and if the U.S. were able in LRIP 11 to commit to years of production, we would get that same reduction in price.”

The Air Force’s IOC in 2016 is on track, he said. However, the service needs 1,100 maintainers trained to support the F-35, including experienced personnel. “We anticipated that many of the experienced maintainers would come from our other fighter platforms to include the A-10,” he said. If the A-10 is not retired, those 800 experienced maintainers will not move to the F-35.

Meanwhile, the Navy is preparing for sea trials aboard the USS Nimitz beginning November 3, when CF3 and CF5 fly to the carrier and are “trapped” on the deck of the carrier. The planes flew from Naval Air Station Fort Worth Joint Reserve Base, Texas, to Marine Corps Air Station Yuma, Arizona on Oct. 30 to undergo maintenance ahead of the trials.

Editor's note: The original article stated that the LRIP 8 contract value for Pratt & Whitney engines was $1.05 billion. That figure is the total value of the contract.

Topics: Aviation, Joint Strike Fighter, Defense Department