Fresh reports of cracks found in the aft pressure bulkhead of Boeing 737 Classics may require operators to perform a new battery of inspections.
The US Federal Aviation Administration (FAA) first issued an airworthiness directive in 1999 requiring repetitive inspections on the web of the aft pressure bulkhead, one of several cracking hot-spots identified on 737-100/200/300/400/500-series aircraft.
More recently, new "cracks have been found in four general areas" of the same bulkhead, the FAA says in a forthcoming notice of proposed rulemaking.
The four new areas of cracking include the web-to-"Y" chord interface, the outer circumferential tear strap, near the dome cap and the "Z" stiffeners near the dome cap, as described by the FAA's proposal.
The cracks have been discovered on aircraft across a wide spectrum of age and usage, including aircraft with between 21,200 and 68,000 total flight cycles and between 17,500 and 61,000 flight cycles, the FAA says.
After the proposed rulemaking is published on 28 June in the Federal Register, the FAA will receive comments over a 45-day period before deciding whether to issue a new airworthiness directive superceding the 1999 order.