The Air Force decided to purchase F-16D longerons after cracking along the jet’s canopy sill forced the service to ground over half its fleet.
Air Force spokeswoman Susan Murphy said Thursday the service decided to purchase new longerons for three aircraft that require the longeron to be replaced due to cracking issues at a different fuselage station, or location on the fuselage. Three additional aircraft, Murphy said, are under engineering evaluation. Murphy said the Air Force is coordinating the new longeron purchases through the Defense Logistics Agency (DLA) and that the current provider of longerons is Aerospace and Commercial Technologies Inc. of Fort Worth, Texas.
The Air Force July 31 discovered these longeron cracks that eventually lead to the grounding of 82 of its fleet of 157 F-16D fighter jets (Defense Daily, Aug. 20). The cracks were discovered between the front and rear pilots seats of the two-seat fighter jet. Murphy said Thursday the tally of grounded jets has increased to 83
The Air Force has not begun installing what it envisioned would be its permanent solution, a strap repair method. Murphy said the strap repair procedure is under evaluation on two aircraft, which are located at Hill AFB, Utah. No timeline for expanding the strap repair method across the fleet has been established, Murphy said.
Murphy said once the Air Force completes the repair process on the first aircraft, and then accomplishes validation/verification in the field, it will have the ability to set a timeline to complete the repairs. Murphy said in August the Air Force envisioned the strap repair method returning approximately 1,000 hours of flight time to the aircraft.
The service also decided against a temporary fix that included removing and replacing 50 fasteners per jet in the area of the cracks. Murphy said this option was deemed “too risky” compared to the gain it would provide. Murphy said all major commands elected to wait for the jets to receive the strap repair.
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.
The F-16D is developed by Lockheed Martin [LMT]. 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.
Lockheed Martin spokesman Mark Johnson said Thursday the company is actively working with the Air Force on a permanent repair solution for the canopy sill longeron cracks. Johnson said the repair drawing, as it is known, is now available and Lockheed Martin will continue to support the Air Force as it works to implement, manufacture and verify the repair installation.
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.