The Air Force is removing and replacing 50 fasteners per jet in the area of cracks found on F-16D canopy sill longerons that the service says will temporarily restore the aircraft to flying status.
Air Force spokeswoman Susan Murphy said Tuesday this temporary measure will be used on a case-by-case basis and each major command will determine if, and when, their respective aircraft will receive this repair. The Air Force July 31 discovered these cracks that eventually lead to the grounding of 82 of its fleet of 157 F-16D fighter jets (Defense Daily, Aug. 20).
Longerons are typically made of aluminum alloy, run the length of the jet and are a type of support structure between the frame and skin of the aircraft. Longerons help prevent tension and compression from bending the fuselage. A canopy sill is the support structure surrounding contact points between the frame and canopy.
Murphy said there are no plans to procure additional longerons as a long-term fix. The permanent repair, Murphy said, which is still in the development phase, will involve a strap to be installed on the longeron. The strap repair method, Murphy said, will return approximately 1,000 hours of flight time to the aircraft, which she called “substantial.”
During this 1,000-hour period, Murphy said, the Air Force will determine if new longerons are needed and will make procurement arrangements accordingly. Murphy declined to say if F-16D prime contractor Lockheed Martin [LMT] has identified a potential supplier of longerons or the raw material that will be used. Murphy said new longerons have not been priced since the Air Force is not pursuing that option at the time.
“There’s a lot of ‘what-ifs’ that have to be dealt with,” Murphy said in an email. “So getting into cost, lead-time, raw-material or responsibility for new longerons is premature at this point.”
An Air Combat Command (ACC) spokesman said Aug. 20 that the two ACC F-16Ds affected by the longeron cracking were expected to return to flight within four to six months, though he cautioned this does not necessarily mean the rest of the fleet would be out this long.
The F-16D fleet, the two-seat variant of the F-16 primarily used for training, is on average 24 years old with more than 5,500 hours of flight time. There are a total of 969 F-16s of all variants in the Air Force.