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GFA AD 686 Issue 4

CRACKING OF FILLER AT WING ROOT

The Australian Air Force Cadets have found signs of cracking of the filler between the lower spar cap and lower wing skin at the wing root.  A repair scheme from the manufacturer was implemented on one aircraft and this repair ‘failed’ shortly after return to service.  The Australian Air Force Cadets suspended operation of their ASK-21Mi fleet on 8 Oct 2018 due to concern that the cracking at the lower spar at the wing roots was not fully understood and may jeopardise safe operation of the aircraft. Issue 1 of AD 686 mandated a visual inspection of the lower spar caps at the wing roots.  Results found two ASK-21 aircraft in addition to the original ASK-21Mi, where the cracking had carried around the spar cap and along the spar web joint with the root rib.  Several aircraft were reported with noticeable crack growth in between the spar cap and skin between annual inspections. Issue 2 of AD 686 changes the initial inspection to before next flight for ASK-21.  Issue 2 also allows aircraft with cracks confined to the region above the spar stub and the area around the radius of the spar cap to return to service with ongoing inspections. Issue 3 of AD 686 gives further instruction for cracks running down the spar webs. Issue 4 of AD 686 clarifies repair options where cracks extend under the rib flange.