The Federal Aviation Authority (FAA) has issued several special conditions on the upcoming Boeing 777-9, aimed to demonstrate the aircraft's composite fuel tanks durability.
Special conditions have been issued in order for Boeing to demonstrate the 777-9’s composite fuel tanks can withstand tire debris impact.
As part of the FAA's regulations, it's said that “Fuel-tank surfaces of typical transport airplanes have thick aluminium construction in the tire-debris impact areas that is tolerant to tire debris larger than that defined in these special conditions. Consideration of leaks caused by larger tire fragments is needed to ensure that an adequate level of safety is provided where composite material is used.”
The FAA has stated that the testing needs to be performed using a tyre fragment sized at 1% of the tyre mass - the fragment then needs to be propelled at the same speed that it would if it came off a tyre during runway operation.
As part of the FAA's rulings, the impact of any fuel tank component within 30 degrees of either side of the wheel planes must not suffer a rupture, deformation or penetration - as well as the impact causing any leak.
The load should also be distributed over an area on the fuel tank equal to 1.5% of the tyre's tread area.
Boeing has been given until July 8th to prove airworthiness through either testing or analysis before the plane can be certified.