The FAA's
airworthiness directive orders
initial and repetitive ultrasonic inspections (UI) of certain part number (P/N) fan mid shafts (FMS) for cracks. This AD requires an initial FMS inspection before further flight. Thereafter, perform repetitive UIs for cracks in the FMS within every 90 days since last inspection. Remove any cracked FMS from service before further flight.
This AD was prompted by a report of an FMS failure and a report of a crack found in another FMS. We are issuing this AD to prevent failure of the FMS resulting in one or more engine failure(s) and possible loss of the airplane.
An unsafe condition exists that requires the immediate adoption of this AD. The FAA has found that the risk to the flying public justifies waiving notice and comment prior to adoption of this rule based on the reported engine failure, the crack find, and that the root cause is still somewhat unknown. We therefore determined that a repetitive inspection interval needed to be established. The repetitive inspection interval is less than the time it would take to process a proposed AD. Therefore, we find that notice and opportunity for prior public comment are impracticable and that good cause exists for making this amendment effective in less than 30 days.
This AD is effective September 21, 2012.
(Excerpts from the AD)