Action
Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.
Summary
We are revising an earlier proposed airworthiness directive (AD) for certain The Boeing Company Model 757-200, -200PF, and -200CB series airplanes powered by Rolls-Royce engines. That NPRM proposed to supersede an existing AD that requires repetitive inspections of the shim installation between the drag brace fitting vertical flange and bulkhead, and repair if necessary; for certain airplanes, an inspection for cracking of the four critical fastener holes in the horizontal flange, and repair if necessary; and, for airplanes without conclusive records of previous inspections, performing the existing actions. That NPRM proposed to reduce the repetitive inspection interval, add repetitive detailed inspections for cracking of the bulkhead, and repair if necessary; extend the repetitive intervals for certain airplanes by also doing repetitive ultrasonic inspections for cracking of the bulkhead, and repair if necessary; and an option for the high frequency eddy current inspection for cracking of the critical fastener holes, and repair if necessary. That NPRM was prompted by 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 action revises that NPRM by adding a terminating action for certain repetitive inspections. We are proposing the supplemental NPRM 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. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.