Defence

A fourth wave of inspections has begun on US Air Force Boeing F-15 Eagles, as the service widens the search for fatigue cracking. So far cracks have been found in the fuselage longerons of eight F-15C fighters.

This will be the third time USAF F-15A-D fighters have gone through checks, but even if cleared they will not return flight until after an investigation into the 2 November crash of an F-15C due to structural failure is completed.

F-15E Strike Eagles have been returned to flight, and Air Combat Command says 222 of its 224 E models have been inspected and cleared for operations. The remaining two are in depot maintenance.

© US Air Force

Of the USAF's 442 F-15A-D models, 435 have undergone the first inspection (seven are in depot), and 425 of those have undergone a second inspection, called a time compliance technical order (TCTO).

The ACC says these two TCTOs resulted in the discovery of longeron cracks in the area of the canopy on eight F-15Cs: four with the Oregon Air Nation Guard; two at Kadena AB in Japan; one at Tyndall AFB, Florida; and one with the Missouri Air National Guard, which also operated the aircraft that crashed. All the affected aircraft were built between 1978 and 1985.

The latest TCTO check, the third involving the A-D models, began on 11 December and expands the inspection area on the longerons. This comes after additional defects were found during examination of the F-15C that crashed after breaking apart in flight. The new non-destructive inspections will take 18h for single-seaters and 22.5h for two-seaters.