“Boeing certified the 747-8 Intercontinental with the tail fuel tanks locked out because during design review of flight test data…it was discovered that, under a certain regulatory-required structural failure scenario, the airplane can experience flutter events when the fuel tanks in the horizontal stabiliser are filled over 15% of their capacity,” said Boeing.
To comply with US Federal Aviation Administration regulations, Boeing will deactivate the tail fuel system to satisfy the requirement that no structural flutter be present in the airframe after any single failure condition.
“These conditions do not present themselves when the tanks are empty,” Boeing said of the structural failure evaluations, which were only found to occur if the aircraft’s wing-to-strut join fitting had failed.
The “requirement for all key structural fittings…need to have a design tolerant of ‘any single failure’”, said Boeing. “We’re actively working on ways to activate the fuel tanks for the long term.”
The lock-out will be achieved through the pulling of a circuit breaker and the physical disconnection and capping of fuel lines running to the horizontal stabilizers’ 3,300gal tanks.
The document listed the maximum structural payload for the passenger configured model as 82.1t (181,000lb) and the pre-service bulletin for the 747-8F at 134t (295,200lb), which increased after April’s update to 139t (306,000lb).