The US Marine Corps still plans on having 10 war-ready Lockheed Martin F-35 Lightning II jets by 1 July, 2015, but the loss of 45 flight testing days may mean that long-emphasised date will slip by days or weeks.

In the context of a programme that has had a “tragic past” and has missed developmental milestones by years, overshooting the Marine Corps initial operating capability (IOC) deadline by days or weeks is still considered a success, Lt Gen Christopher Bogdan tells reporters.

“From an overall programme perspective”, Bogdan says “missing a date by days and weeks compared to the tragic past this programme has had where we’ve missed things by years, I’d say we’re getting better.”

“July 1, 2015 is a tough date to hit,” he says. “There’s no way in the world we’re missing that by months. It’s not going to happen.”

The service, which will be the first to receive operational F-35s, already had taken concessions in order to bring its short-takeoff and vertical landing version online in 2015. Their initial F-35Bs will fly with a less-capable version of the avionics software and will have to be retrofit with the final configuration.

“We’re talking weeks, here,” he adds. “My commitment is July 1, 2015, and if I miss that date, I’m going to apologize to the US Marine Corps.”

Meeting the Marine Corp’s IOC goal started to look untenable when in June a third-stage rotor in the Pratt & Whitney F135 engine of an Air Force conventional takeoff and landing F-35A shattered prior to a test flight. The titanium rotor punctured an aft fuel tank and sparked a fire. The entire 100-plus fleet of test aircraft and fielded jets was subsequently grounded and continues to fly under performance restrictions. That cost the programme 45 days of critical testing needed to confidently meet the 1 July IOC date, Bogdan says. He says the programme will go on a "surge war footing" in an attempt to make those days up.

“We underestimated, in the design of the engine, how much rubbing could potentially occur,” he says.

To get the test fleet back to flying a full profile, those engines will be “burned in” during two flights of defined profiles to pre-trench the stator surrounding the rotors. The process takes two flights of about an hour each, Bogdan says. Four test aircraft have already undergone the process.

New engines will be “pre-trenched” so that the rotor blades will not rub against the stators during complex flight manoeuvres. All 19 test aircraft should have one or the other fix within the next two months, Bogdan says. If navy and air force air worthiness authorities OK either fix, they will be applied to fielded jets, he says.

The pre-trenching method requires fabrication of a new stator, of which Pratt & Whitney produce only about one per week. Retrofitting a fleet of more than 100 aircraft, therefore would take more than two years. It is unclear when a permanent fix, which could mirror the pre-trenching method, will be cut into the engine production line, Bogdan says.

Negotiations on the eighth lot of engines, which are purchased separately from the Lockheed airframes, has been completed. The $1.05 billion deal is for 48 engines and achieved a price reduction of 4.5 percent from the previous lot of 36 engines, Bogdan says.