A new Defense Department report found the F-35B’s short takeoff and vertical landing (STOVL) system could suffer catastrophic failure due to fragment-induced damage of a lift fan blade.
The fiscal year 2013 annual report from the office of Pentagon Director of Operational Test and Evaluation (DOT&E) Michael Gilmore, released Wednesday to Congress, said ballistic tests on an F-35B STOVL propulsion system showed that single fragment damage to the lift fan did not degrade propulsion system performance. But analyses showed that fragment-induced damage could result in the release of more than 25 percent of a single lift fan blade, resulting in a catastrophic failure of the lift system.
More severe threats encountered at low-altitude or in air-to-air gun engagements, the report said, will also likely cause catastrophic damage. The report said the F-35 has no sensors to warn pilots of lift fan damage before conversion to STOVL flight upon return for landing. This is a problem because conversion to STOVL flight puts high loads on the quickly-accelerating system components that can result in catastrophic failure before the pilot can react and return the aircraft to wing-borne flight, according to the report. It can also create uncontained damage that cascades into other critical system failures, the report said.
Prognosis and health management sensors that monitor component health and system degradation could provide some warning, the report said, but the relevant software and hardware would have to be improved to provide reliable information to the pilot to support critical survivability decisions. The F-35 is developed by Lockheed Martin [LMT] with subcontractors BAE Systems and Northrop Grumman [NOC]. The F-35B STOVL system is developed by Rolls-Royce.
Air Force Lt. Gen. Christopher Bogdan, F-35 program executive officer, said Thursday in an email there are no surprises in the report and although it is factually accurate, it does not fully highlight the F-35 enterprise’s efforts to address and resolve the known technical and program-related challenges. Bogdan also said the basic design of the F-35 is sound and test results underscore the Joint Program Office’s (JPO) confidence in the ultimate performance valued by the United States and its international partners.
DOT&E performed a series of vulnerability testing on the F-35’s F135 engine. These tests were comprised of fuel ingestion tests to examine the vulnerability of the engine caused by fuel leakage from ballistically-damaged fuel tanks adjacent to the engine inlets. It also included ballistic tests to determine the damage tolerance of engine components, including fluid-filled components, sensors, actuators and rotating components.
The report said fuel ingestion tests demonstrated the engine can tolerate a range of inlet fuel flows. These fuel flow rates simulated quantities representative of missile fragment-induced damage to fuel tanks adjacent to the engine. System level ballistics test events planned for fiscal year 2015 using a structural F-35C carrier variant test article with an operating engine will quantify the exact relationship of the simulated leak rates to those expected in an actual threat encounter.
Tests using single missile fragments showed that the F135 engine’s rotating components were tolerant to threats possible during low-altitude close air support missions and within-visual-range air-to-air combat, the report said. This type of fighting in low altitude, high speed and high engine thrust situations can result in higher leak rates, the report said. But testing found three of four tests against fuel-filled external components resulted in massive fuel leaks, and one produced a sustained fire. The F-35C system level tests in FY ’15 will evaluate whether installation effects, resulting in leaked fuel interacting with the engine exhaust, would increase the risk of fire.
Pratt & Whitney spokesman Matthew Bates said Thursday in an email that during the course of the DOT&E F135 tests, which he said are intentionally designed to stress and damage the engine hardware, the engine and the STOVL lift system met government requirements for survivability against these threats. Pratt & Whitney, a division of United Technologies Corp. [UTX], remains confident in the capabilities the F135 provides the warfighter, Bates added.
DOT&E suggests DoD develop a plan to improve the integrated caution and warning system to provide the pilot with necessary vulnerability information. The vehicle system should have the capability of detecting and reporting to the pilot any component ballistic damage, such as to the lift fan shaft, that could lead to catastrophic failure upon attempt to convert to STOVL flight.
The DOT&E report also questioned the reliability of the software being developed to operate the F-35 and said problems could force a delay in the Marine Corps’ plans to declare initial operational capability (IOC) for the F-35B in 2015 with the Block 2B software version. The Air Force is planning IOC in 2016 for the F-35A and the Navy plans to do so with the F-35C in 2019, both with different block upgrades.
“The program plans to complete Block 2B flight testing in October 2014,” the report said. “However, there is no margin for additional growth to meet that date.”
“Projections based on the planned growth rate show that Block 2B developmental testing will complete in May 2015, approximately 7 months later than planned,” the report added. “Projections for completing Block 2B flight testing using the historical rate of continued growth…show that Block 2B developmental testing will complete about 13 months later, in November 2015, and delay the associated fleet release to July of 2016.”
Bogdan said software continues to remain the JPO’s number one technical risk and it has instituted disciplined systems engineering processes to address the complexity of writing, testing and integrating software. Bogdan said the JPO is confident about delivering the F-35’s initial warfighting capability to the Marine Corps by July 2015.
Lockheed Martin said in a statement that it is confident the Block 2B software is on track to meet the Marine Corps 2015 IOC timeframe, and that it is scheduled to conduct 300 mission system flights in 2014–the same level as 2013. Spokeswoman Laura Siebert said 7.4 million of the 8.4 lines of software code for full warfighting capability are being or already have been flight tested.
“Lockheed Martin is confident we will complete flight testing of the software required for Marine Corps initial operational capability this year,” she said.