MIAMI – The Boeing 777 is back in the news this week and it’s all due to missing rivet heads mentioned in a new FAA airworthiness directive (AD).
In a Notice of proposed rulemaking (NPRM) this week, the FAA states, “The FAA proposes to adopt a new AD for all The Boeing Company Model 777 airplanes. A report that an operator found solid rivets with missing heads at the left buttock line 25 on the sloping pressure deck web prompted this proposed AD.”
The Notice adds, “This proposed AD would require doing a detailed inspection of the left and right side sloping pressure deck at certain stations for any damaged solid rivets, and applicable on-condition actions. The FAA is proposing this AD to address the unsafe condition on these products.”
Continuing, the NPRM says that the particular airplane that prompted the proposed rule is a Model 777-300 airplane that had 23 solid rivet locations with missing manufactured heads. The craft had accumulated 21,343 total flight cycles and 53,979 total flight hours at the time of discovery.
Additional missing solid rivet heads were found after a fleet-wide multiple operator message (MOM) request. Four more currently-flying Model 777-300 airplanes and one retired Model 777-200 airplane had the defect.
According to the FAA document, a Boeing analysis showed the root cause to be the 7050 aluminum solid rivets used on the sloping pressure deck web. Those rivets were inadequate for the complex tension loading environment and led to premature fatigue cracking of the solid rivets.
This condition, if not addressed, could result in undetected damaged or missing rivet heads on the sloping pressure deck web. In turn, this could result in loss of sloping pressure deck panels, causing decompression and pressure loss, and loss of the hydraulic systems in the area for wheel brakes (both normal and alternate) and steering. This, potentially, could leading to runway departure and adversely affect the structural integrity of the airplane.
The FAA document says that the agency reviewed Boeing Alert Requirements Bulletin 777-53A0093 RB, dated November 24, 2020. This bulletin outlines the procedures for inspecting rivets in the affected locations. This notice also provides information on repair or replacement of any defective rivets found.
The NPRM goes on to predict the cost of compliance.
The FAA is currently inviting comments on the proposed rule. Comments are due by May 24, 2021. The complete proposed rule can be viewed at the Federal Register Web Site.
Featured image: Boeing 777 N779XX – Photo: Ryan Scottini/Airways