Action
Notice of proposed rulemaking (NPRM).
Summary
We propose to supersede an existing airworthiness directive (AD) that applies to the products listed above. The existing AD currently requires repetitive inspections of the shim installation between the engine strut vertical flange and bulkhead, and repair if necessary. The existing AD also requires, for certain airplanes, an inspection for cracking of the four critical fastener holes in the horizontal flange, and repair if necessary. Additionally, the existing AD requires that the existing action be performed on airplanes without conclusive records of previous inspections. Since we issued that AD, we have received reports of loose fasteners and cracks at the joint common to the aft torque bulkhead and strut-to-diagonal brace fitting and one report of such damage occurring less than 3,000 flight cycles after the last inspection. This proposed AD would reduce the repetitive inspection interval, and add repetitive detailed inspections for cracking of the bulkhead, and repair if necessary. This proposed AD would also provide an option, for certain airplanes, to extend the repetitive intervals by also doing repetitive ultrasonic inspections for cracking of the bulkhead, and repair if necessary. This proposed AD would also add an option for the high frequency eddy current inspection for cracking of the critical fastener holes, and repair if necessary. We are proposing this AD to detect and correct cracks, loose and broken bolts, and shim migration in the joint between the aft torque bulkhead and the strut-to-diagonal brace fitting, which could result in damage to the strut and consequent separation of the strut and engine from the airplane.