Airbus A380 wing rib case history
Cracks were first discovered in December last year, on a Qantas-owned Airbus A380 that was being repaired after an engine explosion in Singapore. The Rolls Royce engine failure was caused by a fatigue failure in a fuel line pipe.
The European Aviation Safety Agency EASA took steps and grounded 20 A380 aircraft for visual inspection. These aircraft were early-delivery airframes (airframes without engines). This initial directive allowed up to 6 weeks for visual inspections to be carried out on aircraft which had flown between 1,300 and 1,799 flights. Aircraft which had completed more than 1,800 flights had to be inspected within 4 days.
During this initial round of checks, cracks were found in most of the aircraft. As a result EASA revised their Air Worthiness Directive requiring all 68 Airbus A380 aircraft in service to be inspected. Inspection of the wings was accomplished using high-frequency eddy current inspection equipment. This is a commonly used non destructive evaluation technique used to detect small surface cracks found on the Rib feet (L shaped brackets extending from the wing rib to the wing skin.) Checking the status of components allows you to investigate the current state of the components and the overall wing system, however an understanding of the loads the wing ribs are seeing during take off and landing is more valuable in order to predict the behaviour and measure the potential risks for failure.
How is it Airbus has so much confidence that these crack do not posses any significant danger? The answer is in advanced fatigue analysis which enables complex systems to be theoretically cycled through a lifetime of use in order to understand how the structure will cope with the predicted loadings it sees. This kind of analysis is done at the wing development stage in order to make sure it is going to meet performance targets at the physical testing stage.
The A380’s structural static tests on began in November 2004, in preparation for the first flight clearance.
The tests included: Flight Test Installation (FTI) calibration test, maximum wing bending at limit load, ailerons and spoilers functioning test during max wing bend, fuselage pressure test, and fatigue tests and flight cycles simulation.
Fatigue testing examines how the aircraft structure responds to stress over a long period of time and during different stages of its operations, such as taxiing on the runway, take-off, cruising and landing.
To re-create these conditions, a combination of loads is placed on the airframe and activated by 184 computer-operated hydraulic jacks. The A380’s fatigue testing lasted 26 months up and was conducted to 2.5 times the design service goal.
Testing accumulated a total of 47,500 flight cycles: 2.5 times the number of flights that an A380 would make in 25 years of operations. A 16-hour flight was simulated in just 11 minutes. The tests pushed the aircraft structure to its limits to identify any necessary design improvements.
Final test and preparation for flight is a phase that includes calibration of the gauges, cabin pressurisation testing, and testing of navigation systems.
TRaC has extensive experience in conducting both fatigue analysis studies and physical fatigue testing and has worked with many Aerospace, Rail and Automotive companies to ensure they meet the performance criteria.