The United States Federal Aviation Administration (FAA) has issued an urgent airworthiness directive (AD) to address potential fuel tank explosions on some Boeing 777 aircraft. The AD was issued to address errors made by Boeing in a Requirements Bulletin (RB), which meant that the fuel tanks on some Boeing 777 aircraft were not properly protected against lightning strikes.
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Initially, the FAA issued an AD in September 2022 to address the cracking of various parts of the underwing longeron located at station 1035. This was prompted by reports of cracks found on a Boeing 777-300ER's front spar lower chord that was undergoing underwing longeron replacement. However, Boeing has since discovered that its RB from October 2021 contains errors relating to the application of cap seals to fasteners penetrating the center wing fuel tank, which introduces a second, urgent unsafe condition.
The FAA has determined that it needs to supersede the September 2022 directive to address this new unsafe condition. The regulator now requires an inspection and replacement/modification of the center wing fuel tank fastener cap seals. The FAA highlighted three procedural errors relating to the fastener cap seals and has issued requirements for operators to ensure the minimum required thickness and sealant type, as well as replace any seal that was already replaced with improper thickness.
This urgent AD from the FAA highlights the importance of ensuring the safety of aircraft and their passengers. All necessary measures must be taken to prevent potential fuel tank explosions on Boeing 777 aircraft.