About 60% of the US Air Force's fleet of 442 Boeing F-15A-D Eagle fighters have been cleared to return to flight after more than two months of stand-downs and structural inspections.
The USAF has determined that a Missouri Air National Guard F-15C crashed during air-combat training on 2 November 2007 because of structural failure caused by cracking of a forward fuselage longeron.
Air Combat Command has cleared only those F-15A-Ds - 259 aircraft - that have passed all inspections and met longeron manufacturing specifications.The inspections, which are 90% complete, have uncovered nine F-15s with longeron cracks.
"Additionally, approximately 40% of inspected aircraft have at least one longeron that does not meet blueprint specifications," says ACC. These aircraft have longerons that are thinner in places than specified in the original manufacturing drawings.
ACC says each affected F-15 will have to be analysed to determine if there is sufficient strength in the non-specification longeron to allow the aircraft to return to flight, possibly with subsequent repetitive inspections for cracking.
© US Air Force
The command says it has not decided whether it will repair the F-15s with cracked longerons and any of those that cannot be returned to flight after further analysis. A number of F-15s are scheduled to be retired in 2009 under the next round of base closures. "We need to determine the cost to fix and the return on that cost. That will take another month," says ACC.
Because of the prolonged grounding, about 75% of US Air Force and Air National Guard F-15A-D pilots have lost their currency. "Another week and it would have been 100%," says ACC. The F-15 grounding has been the longest for any USAF post-war jet fighter.
The critical requirement is landing currency, required for solo flight, the command says. Instructor pilots have retained their currency and now the grounding is lifted will take pilots up in two-seat F-15B/Ds so they can perform a single landing and regain their currency. Training to regain operational proficiency can then begin.