The Pentagon says that Lockheed Martin’s F-35 Joint Strike Fighter has previously undisclosed problems with its handling, engine and avionics. This is in addition to earlier problems that have increased delays and cut American orders.
The Pentagon’s Office of the Director of Operational Test and Evaluation released a report this week, stating that both the US Air Force’s F-35A conventional takeoff and landing variant and the Marine Corp’s F-35B short takeoff and vertical landing model suffered from transonic wing roll-off and greater than expected sideslip during medium angle-of-attack testing.
The report added that various components are not as reliable as anticipated and that the Pratt and Whitney F-135 engine has encountered an afterburner “screech,” in which airflow disruptions cause severe vibrations, preventing the engine from reaching maximum power. That problem has delayed some required testing, but the issue is being fixed, the Air Force Times reports.
Another problem concerns the F-35’s helmet-mounted display. The report does not say what the problem entails, but says the issues must be solved before the Block 2 mission systems software can be tested. Currently, the programme is testing preliminary Block 0.5 and Block 1 mission systems software. Block 2 would incrementally increase the aircraft’s capabilities and would be followed by the fully mission-capable Block 3 software. A Lockheed Martin official could not immediately describe the technical problems with the display. “The challenges are being worked [out] with the supplier,” Lockheed Martin spokesman John Kent told Aviation International News.
The report also calls for a redesign of the Joint Strike Fighter’s On-Board Inert Gas Generation System (OBIGGS), which generates inert gases to prevent oxygen building up inside the fuel tanks.
“The OBIGGS system fails to inert the fuel tank spaces throughout the combat flight envelopes evaluated,” the report says, and recommends a redesign.
The issues discussed in the report come on top of problems with the F-35B’s weak structural bulkhead and problems with auxiliary air inlet doors on the aircraft’s top surface. Cracks had been found in the bulkhead after testing, the Marine Corps Times reports.
Earlier this month US Secretary of Defence Robert Gates announced the second restructuring of the F-35 programme within a year. He noted that development of the F-35A and carrier-based F-35C was proceeding relatively smoothly, but there remained significant problems with the F-35B. He said testing issues with the F-35B may lead to a redesign of the aircraft’s structure and propulsion, changes that could add yet more weight and more cost to an aircraft that has little capacity to absorb more of either, according to the Air Force Times.
The F-35B’s development testing has been decoupled from the F-35A and F-35C to ensure progress is not slowed down on these conventional and carrier variants.
This is causing concern amongst the Joint Strike Fighter’s international partners, and in October last year the British Ministry of Defence said it was dropping the F-35B version in favour of the safer F-35C, according to Aviation International News.
Gates said that if Lockheed Martin did not fix the problems with the F-35B within two years, the variant would be cancelled. On January 10 Lockheed Martin said it had fixed the B model’s structural problems by redesigning the aluminium bulkhead where the main landing gear attaches to the airframe, according to the Marine Corps Times.
Due to all the problems the F-35 has been experiencing, the US Air Force has said that the initial operational capability of its F-35A model will be delayed.