Cracks in F-16D canopy sill longerons that caused the Air Force to ground more than half of its fleet were first discovered July 31, according to a service spokesman.
The Air Force said Tuesday it recently removed 82 of its 157 two-seat F-16D fighter jets from flight status due to the discovery of canopy sill longeron cracks found between the front and rear pilot seats.
Air Force spokesman Benjamin Newell said Wednesday within 24 hours of the longeron issues first being identified and routed through the notification process, a Time Compliance Technical Order (TCTO) was issued, resulting in the F-16D maintenance stand down and the beginning of inspections. Following the TCTO, individual F-16 units conducted inspections on the Air Force’s 157 F-16Ds to ensure the structural integrity of the aircraft and public safety, according to a service statement.
As of Monday, all aircraft have been inspected. Eighty-two were found to have cracks; the remaining 75 aircraft have been returned to flight status. The other F-16 variants were not affected. Newell said the two Air Combat Command (ACC) aircraft affected by the longeron cracking are expected to return to flight within four to six months. An ACC spokesman said this does not necessarily mean the rest of the Air Force’s affected F-16Ds will be out this long.
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. Newell said a canopy sill is the support structure surrounding contact points between the frame and canopy.
The Air Force F-16 systems program office and Lockheed Martin [LMT] are analyzing the F-16 structure and developing repair procedures to allow aircraft with cracks to resume operations for a limited number of flight hours while analysis continues on a permanent fix. Air Force Lt. Col. Steve Grotjohn, the deputy chief of the Weapons Systems Division, said in a statement cracks develop due to fatigue from sustained operations as aircraft accumulate flight hours.
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. Lockheed Martin develops the F-16D.