Reader comments -- F-35 engine: 2014 year in review - Note: DOD handbook comment at end

Don Bacon

re: They don't work very well.
I just completed a timeline of news reports on the F-35 engine, one of its worst shortcomings.

F135 engine failure timeline
background
The F135 is the largest, heaviest and hottest high-performance fighter engine ever built, weighing 70% more than the P&W F100 and measuring 24% larger in diameter, with consequently larger inertial and gyroscopic forces.

During 2007-2009 repeated problems with turbine blades contributed to significant delays in the F-35 test program and a partial redesign of certain parts of the engine. The grounding in February 2013 was caused by crack, found in a Low Pressure LPT3 turbine blade. Investigations of the latest engine fire seem to focus at the same problem.

The fleet was grounded from Feb. 21-March 1, 2013, due to the discovery of a 0.6-in. crack on a third-stage low-pressure turbine blade on AF-2, an F-35A used for testing, at Edwards AFB, California.

On Feb 19, 2014, a crack on the 3rd stage low-pressure turbine airfoil was found during an inspection of a conventional F-35A at Edwards AFB, Calif., says Matthew Bates, a spokesman for Pratt & Whitney, which makes the stealthy, single engine fighter’s F135 engine.

June 23, 2014 -- A Pratt & Whitney F135 engine on an Air Force F-35 A-model jet broke apart and caught fire. The fire occurred in an F-35A Lightning II as the pilot was attempting to take off from Eglin Air Force Base in Florida. The fire, which occurred at9:15 a.m. local time, first prompted "safety pauses" to flights for the fleet directed by local commanders.

June 25 -- JPO says preliminary assessment on fire will come by end of week but root cause analysis may take longer.

Jun 26 -- The Air Force, Navy and Marine Corps have halted all F-35 flights . . . The F-35 fire was on AF-27 a recent delivery from LRIP-5, which included contracts for 32 aircraft from Jul 6, 2010 to Jun 10, 2013.

Jun 27 -- Sources familiar with the situation said engine pieces and fragments were found on the runway at Eglin Air Force Base in Florida after the fire.

Jul 7 -- A June 23 fire that severely damaged a Lockheed Martin F-35 Joint Strike Fighter at Eglin Air Force Base, Fla., is “definitely” related to the aircraft’s Pratt & Whitney F135 after-burning turbofan, multiple sources told USNI News. “We are working closely with the Air Force Safety Investigation Board to determine root cause and inspect all engines in the fleet. Safety is our top priority,” company spokesman Matthew Bates told USNI News on Monday.

Jul 10 -- The blaze on an F-35 Joint Strike Fighter that grounded the military’s fl eet might be an isolated incident, the Pentagon’s chief weapons buyer Frank Kendall told lawmakers Thursday.“There’s a growing body of evidence that this may have been an individual situation, not a systemic one.”

Jul 11 -- “We're not going to put the F-35 in the air [or] send it anywhere until we are absolutely convinced and know that it's safe to fly,” SecDef Hagel said. . . The U.S. Navy on Friday maintained a grounding order for F-35 B-model and C-model fighter jets built by Lockheed Martin Corp given that it remained unclear what had caused a massive engine failure on an Air Force F-35 jet on June 23.

Jul 13 -- The engine fire that prompted the U.S. military to ground its entire F-35 Joint Strike Fighter fleet was caused by “excessive” rubbing of fan blades in the jet’s engine, the Pentagon’s top weapons buyer said.. . detailed inspections of engines on the fleet of 97 F-35s already built had not shown signs of the kind of excessive rubbing founded on the engine that broke apart, although there were signs of milder rubbing in several other engines. . .“From the evidence we have so far, we don’t see at this point what I would call systemic difficulties,” Defense undersecretary Frank Kendall told reporters in London. “We’re not noticing it throughout the fleet.”

Jul 14 -- Engineers were working t o carefully dismantle AF-27 in order to examine aircraft components that might have started the fire. Investigators had begun conducting engine borescope inspections, as well, he said. “The aircraft is pretty well burnt because of a fuel tank fire,” he noted. . .this particular IBR encountered “more severe” rubbing than planned, leading to higher temperatures, cracks — and eventually a major fire. . ."There is a growing body of evidence that this is not a systemic, major design problem," said Frank Kendall, the Defense Department's top weapons buyer....The incident is the second in less than a year to affect a part of the engine known as the integrally bladed rotor, or IBR.

Aug 25 -- “We know how to prevent it from occurring again by making a redesign in the en gine. And, that is what the engine company is working on," said General Mark Welsh, Air Force chief of staff. “I think they are probably pretty close to that, and then they will have to make changes to the manufacturing process to ensure that that is good for the future.”

Sep 3 -- General Bogdan, program executive, said that the plane that blew up was damaged during two seconds of flight when the test pilot — operating well within the safety envelope of the plane’s abilities — put G forces, yaw and roll stresses on the plane all at the same time. “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 j ust 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. Pratt & Whitney is designing a fan section with a built-in trench to avoid the rubbing. It must be done very carefully, to avoid allowing air in — which is why the engines are designed the way they are now. The fix will be made to the fan module, which will be replaced in all the 156 engines should the tests prove out, Bogdan said. Also Bogdan said the retrofits should be relatively easy and inexpensive to carry out since the engine is built in modules, which will allow mechanics to swap out the entire fan section.

Sep 4 -- General Bogdan, speaking at the National Press Club in Washington DC, says the Department of Defense, Lockheed and engine manufacturer Pratt & Whitney knew from the program’s outset that it would experience delays. "We are going to have problems beyond this, there's no question," he adds. Bogdan says the root cause of the engine malfunction will be identified by the end of September. A final design for the fix is expected in late October, and P&W is already testing a possible fix.

Sep 8 -- The long-delayed operational debut for the Lockheed Martin F-35 Joint Strike Fighter is at risk of further slippage due to a safety-critical problem with i ts Pratt & Whitney F135 engine for which no single root cause has yet been identified. The reason why moderate-g maneuvers would be related to the “hard rub” and overheating has not been definitively identified, but a causal linkage between maneuver loads and clearances inside the engine points to distortion or displacement of engine components.

Sep 9 -- Bennett Croswell, president of Pratt & Whitney Military Engines, said the engine failure came about eight hours after an unusual maneuver involving a roll, yaw and heavy gravity loads during sharp turns. "This is a maneuver that the engine should be able to withstand," he said.

Sep 9 -- Pratt's Croswell said Pratt had already completed a baseline test of the current engine at its West Palm Beach, Florida facility, and had begun testing possible fixes. Croswell said the engine failure came about eight hours after an unusual maneuver involving a roll, yaw and heavy gravity loads during sharp turns. "This is a manuever that the engine should be able to withstand," he said.

Sep 11 -- Pratt & Whitney says the "root cause" of the June 23 engine failure on a Lockheed Martin Corp F-35 fighter jet should be clear by the end of September. P&W was awarded a $65,566,174 engine contract.

Sep 15 -- Bogdan said a fix to the engine issue that caused the fire should be decided by mid-October and expressed confidence it would not impact the Marine Corps’ planned initial operational capability date of July 2015. Bogdan says at AFA that June engine fire "absolutely not" indicative of Pratt quality problem. Bogdan: Hard rub in F135 engine that caught fire was due to extreme flex in the engine during a maneuver. Pratt & Whitney is developing a replacement component for the fan section of the F135 engine. “We’re hoping before the end of the year, we’ll have at least the prototype.” Pratt's Croswell: three F35 engines were found to have signs of similar damage to what caused the AF-27 fire.

Sep 16 -- Bennett Croswell, president of Pratt & Whitney military engines division, which manufactures the joint strike fighter’s F135 engine, said he believes that weeks before the fire, a pilot performed a “relatively aggressive maneuver” that may have caused the seal plate within the third-stage fan to overheat and form “micro cracks.” In time, those micro-cracks propagated to other third-stage fan components, including a titanium arm that broke apart from the engine and pierced through the fuel tank, starting the June 23 fire. Croswell stressed that although the maneuver “had a lot of pitch, yaw and Gs to it,” it was still within the flight envelope of the jet. Bogdan: "Fighter engines [are] actually not static things when you put them in an airplane,” he said. "When you pull Gs on the airplane or you yaw or you roll the airplane, the engine actually flexes." What was unexpected was the excessive heat caused by the “hard rub,” he said. “Quite frankly it was underestimated. It’s as simple as that.” The seal plate normally functions at about 1,000 degrees Fahrenheit, but the cracks were formed by temperatures closer to 1,900 degrees. Croswell said the engine issue was a design challenge. The probable retrofit schedule for test aircraft appears to be far later than hoped for.

Sep 19 -- Bennett Croswell, P&W president for military engines, said that “there’s more movement of the engine” within the F-35 airframe “than we thought when we designed it.”

Sep 22 -- An official with the Joint Strike Fighter's program office said Monday that its investigation into a June engine fire that grounded the fleet has narrowed a long list of potential causes for the incident down to just four. Navy Capt. Bryant Hempstall, the F-35 program's weapons systems program manager for logistics, said the investigation with Pratt & Whitney is closing in on a cause, which still could be weeks away."Within the next couple of weeks, we believe we are going to come to a resolution and know what that is."

Sep 25 -- Engineers have identified two potential [work-arpound] remedies to prevent a repeat of the fire.

Oct 9 -- The U.S. military needs a "lasting" fix to the engine issue that grounded the F-35 fighter fleet for several weeks this summer... a top U.S. Navy official [Rear Admiral Mark Darrah] said this week. Darrah said he had never [before] seen the underlying technical issue - which involved excessive rubbing of two parts in the F135 engine that led to chemical changes in their composition - but remained confident that it could ultimately be resolved. Joe DellaVedova, spokesman for the F-35 program office, had no immediate comment on when the analysis of the root cause of the incident, and the proposed solution, would be completed, but said officials were getting closer. "We're nearing the end of that process," DellaVedova said. Once the fix is decided, the Pentagon is expected to sign a contract with Pratt for the next batch of F135 engines, as well as a separate deal with Lockheed for 43 more jets. [It signed it without an announced fix, a $1.05 billion contract with Pratt & Whitney on Oct 30]

Oct 14 -- Investigators have pinned down the probable cause of the engine problems that triggered a fire on a F-35 fighter jet, paving the way for the Pentagon to resume awarding deals for new aircraft and engines. A joint team investigating the engine failure had met and agreed on the cause of the engine failure: that prolonged rubbing of certain material in a part of the engine had led to small cracks which eventually caused the third stage fan rotor to break apart. F-35 program office were executing a plan to modify the current operational and test jets, and implement a long-term solution for future jets. No details were provided on the exact nature of the fix adopted, or its cost, but officials have said they did not expect the engine modifications to be very expensive. P&W was awarded a $591,919,496 engine contract.

Oct 15 -- A fix for the engine has been expected, with a Pratt executive outlining potential designs for reporters during September’s Air Force Association conference. But that fix was on hold until the root cause analysis to determine exactly why the microcracks occurred. The Pentagon office is working with Pratt to implement a plan to modify the fielded engines while also putting through a long term solution for newer copies of its F135 engine.

Oct 16 -- Officials have not yet outlined a clear path forward to address the design issue that led to an engine fire that grounded the fleet of single-engine aircraft this summer. Program officials have, however, approved a workaround to an engine retrofit that will get the test fleet back to unrestricted flight soon, according to a government source.

Oct 29 -- The initial problem with this aircraft occurred three weeks prior to the fire when a pilot conducted a routine ridge-riding maneuver that combined yaw, roll and gs. Such a maneuver had not been done on such a new aircraft.

Oct 30 -- By the end of December, Bogdan hopes to have determined what option or combination of options the JPO will select. A long-term solution for new production models will require more discussion, Bogdan said, noting that Pratt has five different possible solutions being looked at. He hopes to have one selected by the end of 2014. Engines with that fix should start coming off the line at the end of 2015. P&W was awarded a $793,051,336 engine contract.

Oct 31 -- Bogdan: “We designed this airplane to rub in certain spots. The third rotor fan section of the engine is supposed to rub against a permanent portion of the engine. We underestimated in the design of the engine how much could rubbing p otentially occur. We saw a hard rub in excess of anything we would have expected to see, resulting in heat that we never expected to get.”....Jets that have not undergone a repair are still operating under flight restrictions limiting g, roll and speed. They also are subject to laborious borescope inspections to the engine after 3 hours of flight.

Nov 25 -- P&W was awarded a $105,492,976 engine contract.

Nov 26 -- P&W was awarded a $11,473,337 engine contract.

Dec 19 -- P&W was awarded a $47,208,684 engine contract.

after Oct 31 -- not a word on a permanent fix engine redesign

summary: 
The June 23, 2014 engine failure and ensuing plane destruction occurred as a result of an earlier maneuver involving a roll, yaw and heavy gravity loads during sharp turns, which the engine should be able to withstand. The engine rotor rubbed excessively against the stator, the blade components cracked, broke from the engine and pierced the surrounding fuel tank, which started the fire.(Sep 16) The amount of flex (Sep 19) and rubbing (Sep 16) were underestimated in the engine design. Initially the Pentagon said the catastrophic engine failure was one-time occurrence (Jul 10, 13, 14) but it was quickly determined that an engine redesign, "a design challenge," (Sep 16) caused by excessive flexibility (Sep 16, 19, Oct 31) is necessary (Aug 25, Sep 3, 4, 15, Oct 14, 15, 16, 30). No fix has been announced by February 1, 2015. The Pentagon has awarded engine contracts to Pratt & Whitney worth a total of over $1.5 billion since the engine failure, with no redesign.(Oct 14, 30, Nov 25, 26, Dec 19)

also: The P&W F135 engine in the F-35 did not contain the engine f ragments which punctured a fuel cell, causing the fire. And this means that the F-35 is not airworthy, because the DOD Handbook MIL-HDBK-516B for Airworthiness Certification Criteria requires the applicant to "Verify that any uncontained failure of an engine control or subsystem component with rotating parts does not adversely affect the continued safe operation of the air vehicle."

-