The F-35 Joint Strike Fighter (JSF) remains the problem child of the US military, with some operational tests abandoned in 2014, and buggy software proving a headache.

The US military's Office of the Director, Operational Test & Evaluation (DOT&E) has released its latest annual report, and the F-35 Joint Strike Fighter chapter describes the Department of Defense's efforts in trying to get the project back somewhere close to schedule.

To avoid a cascading series of delays that would have stretched into 2016, the project abandoned an Operational Utility Evaluation (OUE) planned in April 2014 for the Marines' Block 2B configuration of the aircraft.

The reasoning, explained at Aviation Week, was that Lockheed Martin couldn't put together enough units in that configuration to run the Block 2B OUE in time. If it had proceeded, the OUE would have been pushed back until 2016, in turn delaying the software development effort for “Block 3F”.

Instead, F-35A test aircraft will be used for a “limited assessment”, the report states.

The Block 2B tests were also impacted by restrictions imposed after a June 2013 engine failure in an F-35A unit. That impacted software tests, because the restricted flying hours “reduced the number of accessible test points”.

There were also unplanned software releases to fix bugs, in spite of which “discoveries continued to occur in later versions of software”.

To try and get around software-associated delays, the test program is being revised: some test points are being eliminated, reducing the total number of test points remaining for Block 2B from 529 down to 243; and some fixes are being deferred to the Block 3 program.

Mission “data load” software is also causing concern. This software is loaded on a mission-by-mission basis, working in conjunction with the permanent systems, to operate sensors and respond to conditions for a particular battleground (Aviation Week gives identifying hostile radars as an example).

The DOT&E report says “truncating the mission data load development and conducting open-air flight testing early on a limited open-air range for the purpose of releasing a mission data load in mid-2015 would create significant operational risk to fielded units”. ®