The Defense Department and Pratt & Whitney are still pursuing a long-term solution to the F135 problem that lead to an engine fire and a temporary grounding of the F-35 Joint Strike Fighter last summer, according to a key officer.
Principal Military Deputy Assistant Secretary of the Navy Vice Adm. Paul Grosklags told the House Armed Services (HASC) tactical air and land forces subcommittee Thursday DoD had two temporary fixes in place allowing the F-35 to fly. Excessive flexing of the F135 during flight last summer caused an engine to overheat and develop microcracks as it flexed and rubbed. The microcracks grew so large they started a chain reaction on an Air Force variant F-35A, leading to the fire.
F-35 Program Executive Officer (PEO) for F-35 Air Force Lt. Gen. Christopher Bogdan said last summer DoD would adjust a “burn-in” procedure as a fix because once the engine is burned into the right depth of the wedging (between the fan blade and polyimide material) and the aircraft reaches the edges of the flight envelope without rubbing, it is good to go. Bogdan last summer called this a fix to provide “full-life” as opposed to a short-term solution (Defense Daily, Sept. 5).
Pratt & Whitney said last summer it would have a third-stage fan prototype done by the end of September as a solution to the problem. DoD was to perform tests on it, Bogdan said last summer, and he expected it to be put on a test aircraft and flown by the middle of October. F-35 JPO spokesman Joe DellaVedova Thursday declined to comment on the engine issue.
Pratt & Whitney spokesman Matthew Bates said in an email an in-flight rub-in procedure was initiated on the F-35 fleet to return flight operations to the specific aircraft-cleared envelope. The rub-in procedure involves a single flight that gradually increases the gap between the second stator and the third rotor in the fan section.
Bates added a long-term fix, pre-trenching the stator, is being incorporated into current production engines and into already-fielded product. This process, he said, should be complete by early 2016.
DoD is also having a software issue preventing the F-35 from performing “four ship fusion,” or communicating with four aircraft at once in real time. Deputy Marine Corps commandant Lt. Gen. Jon Davis told the House Marines and their F-35B were currently capable of communicating two aircraft at a time “very well,” but not four aircraft. DellaVedova said Thursday this four ship fusion issue is platform-wide and not limited to only Marine Corps F-35B variants.
DellaVedova said in an email the Marine Corps has deemed the software block 2B capability sufficient to declare initial operational capability (IOC) in July and has tested the F-35B in a number of mission representative scenarios, including close air support (CAS) and air interdiction. The aircraft has demonstrated capability to perform these missions.
DoD is still conducting developmental test, DellaVedova said, and there are there are discoveries and improvement issues. During three or four “ship” led missions, he said, test pilots have experienced “information overload” where some of the information is not 100 percent accurate. DellaVedova said there are already improvements in process to address these discoveries and provide a better correlated picture of the 360-degree battlespace.
The F-35, DellaVedova said, has planned capabilities improvements throughout its development from the block 2B/3I initial warfighting software through the final block 3 full warfighting capability software in 2017.
Pratt & Whitney is a division of United Technologies Corp. [UTX]. The F-35 is developed by Lockheed Martin [LMT] with subcontractors Northrop Grumman [NOC] and BAE Systems.