About 561 older Boeing 747s worldwide face a new series of inspections and modifications to address increasing concerns about cracking along the widebody's stretched upper deck.
The proposed revision to a previously proposed rulemaking by the US Federal Aviation Administration would cost an estimated $25.3 million across the fleet to implement, according to a notice that will be published tomorrow in the Federal Register.
Airlines are allowed to comment on the revision before the FAA issues a formal rulemaking.
The revisions affect older 747 models with stretched upper decks, including the -100B SUD, -200B, -300, -400 and -400D, the FAA said.
The FAA issued a notice of proposed rulemaking in July 2009, which required carriers to inspect, modify and re-inspect frame-to-tension-tie joints at two major stations on the upper deck.
Carriers have since reported that the cracking problem is more widespread.
As a result, the FAA is proposing to add four actions to its previous notice, which include stage 1 inspections, stage 2 inspections, modifications and post-modification inspections.
The required modifications are the greatest source of the potential costs. The FAA estimates that the parts and labour hours to complete the modifications will cost between $24.3 million and $24.6 million across the fleet. The inspections account for the remainder of the costs.