Emergency inspections ordered for 16 Airbus A380s, including one from Qantas, are the next step in a long engineering investigation. Professor Brian G Falzon and Dr Sonya Brown MIEAust offer their view on the evolving story and why these wing cracks are very different from those found more than a decade ago.
As told to Chris Sheedy
Professor Brian G Falzon
Distinguished Professor Brian G Falzon is Executive Dean Faculty of Engineering, Computing and Science, and Chair of Composite Materials and Aerospace Structures at Western Sydney University.
The A380 wing has a front and rear spar which extend along the span of the wing, 36.3 m from fuselage to wing tip, to form the wing-box. A middle spar extends only through the inboard wing-box section, approximately 18 per cent of the wingspan.
In 2019, an airworthiness directive (AD) was issued by the European Union Aviation Safety Agency (EASA) after cracks around outer rear spar areas were reported.
By 2024, with additional information and reporting from operators, successive ADs had expanded inspection requirements to all A380 aircraft and extended the regions to include sections of the outer front spar, inner front spar and outer rear spar.
Inspection thresholds were subsequently brought forward. The interesting change was a shift from inspection thresholds based on the age of the airframe to one which now factored in the time an aircraft spent on the ground.
This time was then further refined to distinguish time spent parked or stored.
The latest AD, escalated to an emergency airworthiness directive, focused on 16 airframes. EASA is requesting this information to gather and analyse more data, develop a deeper understanding of the underlying issues and enable it to revise the inspection program, if required.
Wear and tear or something more?
This is what EASA is trying to determine. Not so much as to whether there is a design flaw but whether expected wear-and-tear has been accelerated due to the grounding and storage of these aircraft over prolonged periods.
In the A380 wing, the spars and ribs are made from high-strength aluminium. The 7000 Aluminium series has a high percentage of zinc and also contains magnesium and copper.
In 2023, Aviation Week reported Airbus had identified hydrogen-assisted cracking, or hydrogen embrittlement, as the cause of accelerated crack development in certain A380 wing spars stored for extended periods.
High strength 7000 series aluminium is referred to as a precipitation-strengthened alloy, but its grain-boundary microstructure can make it more susceptible to environmental assisted cracking.
Aluminium usually protects itself by creating an oxide surface layer, but if this is compromised, for example via pre-existing microcracks, water combined with high temperatures can react with the aluminium surface to generate atomic hydrogen.
This hydrogen diffuses into the metal and can accumulate at grain boundaries or areas of high stress concentration, making these regions more brittle.
READ: This is the proposed world’s largest aircraft, capable of carrying 100 m-long wind turbine blades
Why is this different from 2012?
The regions under scrutiny in 2012 were rib feet, which are like brackets connecting the wing ribs to the wing skins.
Two types of cracks were identified: cracks around the fastener holes and cracks at the edges of the vertical section of the L-shaped rib feet.
At the time, these cracks were attributed to the choice of the 7000 series aluminium alloy and additional stresses which were introduced during the manufacturing process.
Cracking in aircraft can be managed
Dr Sonya Brown MIEAust is Associate Professor in Aerospace Engineering at UNSW Mechanical and Manufacturing Engineering.
An A380 wing is built around a front spar and a rear spar that form the wing box and carry the majority of the flight loads. There is also a shorter centre spar that only goes from the fuselage to approximately just past the inner engine.
The current inspections are focused on regions of those spars in the middle section of the wing, between and slightly beyond the engines, where engineers have identified cracking during maintenance on some aircraft.
What we don’t know is how extensive those cracks are. And we don’t know exactly why these particular 16 aircraft have been singled out as needing inspections imminently.
Long-term storage during COVID is one possibility. Earlier airworthiness directives highlighted aircraft returning to service after extended storage. Flight hours, flight cycles or similarities identified during previous inspections could also be factors.
Can wing spars be replaced?
Aircraft are designed with significant safety margins. We expect them to withstand their limit loads repeatedly throughout their service lives without developing cracks or permanent deformation. Wings are designed to carry 50 per cent more than those expected loads, before failure.
That means cracks shouldn’t occur during normal operations if the loads experienced are as predicted when the aircraft was designed.
However, there can be cases where the cyclic loads are underestimated, or something else impacts the aircraft. This could include conditions that couldn’t be predicted, such as effects of long-term storage that potentially age the materials differently.
Aircraft do have regular and thorough inspection and maintenance programs that allow anything unexpected, such as cracking, to be detected and repaired.
Earlier cracks, identified in 2012 in A380 wings, involved relatively small components connecting the wing ribs to the wing skin. Those parts could be replaced. The current issue involves the wing spars themselves, major structural members that cannot simply be swapped out. If repairs are required following regular inspections, Airbus will instead develop approved repair schemes that reinforce the affected areas.
READ: How the world’s largest aircraft by wingspan was designed
What happens with the data?
The reason commercial aviation remains such a safe form of transport is that every finding is tracked and shared.
If one airline discovers an issue, that information flows back to the manufacturer, the regulator and every operator of that aircraft type. Engineers build an extraordinary database covering flight hours, flight cycles, maintenance history and storage conditions.
Will similar issues emerge again as aircraft continue to age? Almost certainly. But that shouldn’t surprise us. Aircraft are designed to operate safely for decades through regular inspection, maintenance and continuous engineering improvement.
The lessons learned from today’s fleet will almost certainly influence tomorrow’s aircraft. Whether that means changes to materials, structural layouts or the way future aircraft account for long-term storage, every new piece of evidence helps engineers design the next generation even better than the last.
EVENT: Registrations are open for the 21st Australian International Aerospace Congress.
