The US Marine Corps has decided to stand-up the first operational F-35B squadron in July with known software, structural and logistical deficiencies that must be fixed later, says Lt Gen Chris Bogdan, executive officer of the joint programme office.

That decision means the first F-35B unit will achieve its initial operational capability milestone on time in the fourth quarter of Fiscal 2015, but with some operational restrictions, maintenance workarounds and the possibility of an internal redesign of a critical bulkhead, Bogdan says.

In 2010, the USMC accepted that the first operational F-35 squadron would enter service in 2015 with a less capable version of software than demanded by the Air Force for the F-35A and the navy for the F-35C.

That lesser software version – dubbed Block 2B – will be incomplete at the time of IOC. The software performs the basic flight control functions well, Bogdan says, but is unable to handle the most extreme challenge for the F-35’s vaunted “sensor fusion” capability.

The F-35’s mission systems software processes data being collected by various onboard sensors into a complete operational picture that is presented to the pilot. In a scenario with four F-35s flying in formation against both ground and air threats, the sensor fusion system is designed to pass targeting information between aircraft using the multi-platform advanced data link (MADL).

Recent testing has shown, however, that the software algorithms become confused with three or four aircraft sharing data about the same target, Bogdan says. Each aircraft senses the target’s location and characteristics slightly differently, and the algorithms are unable to determine if there is only one target or more than one target.

The F-35B’s pilots have learned to use various work-arounds, he says. For example, four-aircraft formations can be broken down into groups of two aircraft, where the sensor fusion algorithms have proven more reliable, he says.

A completed version of the Block 2B software that fixes the problem should be available by October, Bogdan says.

Meanwhile, Bogdan also says he is worried about the integrity of the F-35B’s aluminium 496 bulkhead, which bears critical structural loads where the trailing edge of the wing attaches to the aft fuselage. In 2004, programme officials reduced the weight of the F-35B by about 1,360kg (3,000lb). Those changes included switching the bulkhead material from titanium to lighter-weight aluminium.

The lighter bulkhead has since proved susceptible to structural cracking, requiring a series of “patches” all over the 496 bulkhead. There are now so many patches that programme officials are concerned it may be necessary to redesign the bulkhead for production aircraft, Bogdan says.

Finally, Lockheed’s autonomic logistics information system (ALIS) is not ready to support a growing fleet of operational and test aircraft, Bogdan says. It will take a few years to resolve the ALIS deficiencies, and until then F-35B maintainers must use workarounds to inspect and repair the aircraft.