The FAA on April 9 proposed an airworthiness directive for inspections of all models of Boeing’s 777 jetliner. The directive is based on the agency’s discovery of five 777s of various models with missing rivet heads used to join the aircraft’s skin. This directive is the second to affect the 777 in less than two months. The previous one was issued following the explosion of a Pratt & Whitney Canada PW 4000 engine in February.
The FAA said it has received a report indicating that an operator found solid rivets with missing heads at the left buttock line 25 on the sloping pressure deck web. The Model 777-300 airplane had 23 solid rivet locations with missing manufactured heads; the airplane had accumulated 21,343 total flight cycles and 53,979 total flight hours at time of discovery.
A fleet-wide multiple operator message (MOM) request found four more Model 777-300 airplanes and one retired Model 777-200 airplane with missing solid rivet heads. Boeing analysis showed the root cause to be the 7050 aluminum solid rivets used on the sloping pressure deck web, which 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, which 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—potentially leading to runway departure and adversely affecting the structural integrity of the airplane. The agency believes the cost to repair each affected 777 could be as much as $33,000 per aircraft. The airworthiness directive could potentially affect nearly 225 individual aircraft. For more information, interested parties should contact Luis Cortez, aerospace engineer, Airframe Section, Seattle ACO Branch, 2200 South 216th Avenue, Des Moines, Washington, 98198. Email contact is Luis.A.Cortez-Muniz@faa.gov.