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Technical Issues

As the A380 in-service fleet has expanded, problems have come to light. To address known problems, as well as the in-service issues, the fleets are undergoing major modification programmes at timed intervals.

 

A380
 © Max Kingsley Jones
FIRST ISSUE

The first notable issue that SIA faced occurred around three months in, just after the second aircraft arrived, when a fault surfaced with the alternate brake system in Sydney. However, Sirisena says that "compared with the early days of the A340-300 or 777, the problems have not been that significant".

Clark says that the Emirates fleet is undergoing "a big mod programme that requires removing an aircraft from service". This should be completed on the five delivered aircraft by February. New aircraft it is due to receive will have the latest modification standard, he adds. Upgrades address issues with software, fuel line pressure sensors and body gear steering, among other things.

SIA now has 10 A380s - more than the number of passenger Boeing 747-400s it has in operation. Its A380 fleet's average daily utilisation is about 14h, while technical dispatch reliability (TDR) is "hovering around 97-98%", says Sirisena.

While that number is "not too meaningful" due to the relatively small fleet size, he adds that it is "still very commendable" and is higher than the 747-400 was at the same stage of its development, although Sirisena points out that modern aircraft have a much-increased level of diagnostics available.

The industry's typical technical dispatch reliability benchmark is above 98.5%, and Clark says that while Airbus is guaranteeing 98.5% "we're not there yet. We're at 97%, sometimes 96%."

The major problem being experienced is the plethora of system nuisance warnings, which are "driving down technical dispatch", he says. "Airbus is very, very anxious to get the issues sorted out," Clark says.

Emirates and SIA both perceive the A380's warning system as being too sensitive, resulting in misplaced fault messages about systems or equipment. "They didn't build enough tolerances into the software, they've made it overcomplex," says Clark. We have false alarms but we're not prepared to dispatch until they're sorted out."

 


Sirisena says: "What we are grappling with are algorithms for failure detection, which not only detects a failure but also acts upon it. Unfortunately this can lead to a perfectly healthy system being shut downor [a no-go fault warning] for a problem that was minor enough to have been deferred.

"Once we identify a problem and understand it, Airbus will quickly come up with a work-around. But it is not so straightforward to reprogram."

 

NUISANCE WARNINGS

Clark says that the problem with the nuisance warnings has been their diverse nature, but "the common thread" is the software. He says Airbus executive vice-president programmes Tom Williams and his team "have sat in my office many times and said they can't identify trends, which is the worst possible thing".

Clark blames the software's design. "There was a philosophy of utopia - I suspect that Airbus was blessed with some boffins who said 'we've got to make this absolutely perfect - no flexibility'. The slightest surge causes one [sensor] to trip and then six more as they're all linked," he says.

"The engineering support teams - both Airbus and Emirates - have had to catch up on this complexity curve of the software. So there is a learning game going on. I've told Airbus it needs an audit of the software on this aeroplane, and I've asked them how they're going to address it."

Airbus has undertaken to raise Emirates' TDR to the 98.5% target by 31 December, but Clark is sceptical this can be achieved. "They've got some work to do," he says.

Qantas is less specific about the problems it has suffered, with Vincent saying that while the airline "did encounter some issues" it "worked closely with Airbus at the time and these were resolved quickly".

Issues included a fuel tank indication system problem that affected two aircraft and a nose wheel steering issue on one, he says.


Airbus's Williams says that this latter problem was caused by water ingress into the rotary transducer on the gear leg that identifies its position. "The water was freezing on long flights, which was causing the sensor to give inaccurate positioning. There's been a design change and in the meantime an inspection procedure has been implemented."

DISPATCH RELIABILITY

Strambi says that the Qantas A380 fleet's dispatch reliability has been "good". A small number of technical issues had an impact on operations for a short period, but generally "we have been happy with the aircraft's reliability, considering this is the first 12 months of operating a brand-new fleet type".

Clark says that while the Emirates fleet has also suffered some "hugely frustrating" failures of components, most are easily dealt with. However, one "pain" has been the repeated failure of the main gear steering system, which can force the aircraft to return to the stand as the steering is a minimum equipment list (MEL) item.

The trailing axle of the two six-wheel centre bogies is articulated to avoid tyre scrub on the inside wheels, and the wedge that must lock the steering in place for take-off has proved problematic, says Williams. "If the wedge doesn't position correctly then the crew gets a warning that requires a return to the gate. The wedge can be locked in place manually to allow the aircraft to be despatched, but this still results in a delay."

 Sirisena explains that the problem has occurred due to "wear and tear issues that surfaced after flight-test" and that Airbus devised an interim "work-around" - to taxi straight for 50m (165ft) before making a turn.

Williams says that the problem has now been fully addressed in two ways. "The wedge sensor was too sensitive so that has been redesigned, and a greasing procedure was worked out which actually did more [to fix the problem] than the sensor. We now think that this problem is behind us," he adds.

Another gear-related problem blighted SIA - and resulted in an in-flight turnback - which was caused by the system for the undercarriage doors, which incorrectly detected them as being open.

"There have been rigging issues on gear-doors and sensors and we've improved the procedures on the production line to make sure we've got the tolerances set up properly," says Williams.

HAPPIER TALE

A happier tale is the A380's performance, which has bettered expectations. "Meeting the performance guarantees doesn't come into it, she's ahead of her nominals," says Clark.

"The faster the A380 flies the less fuel it burns. Long-range cruise is Mach 0.85, if you fly at Mach 0.83 the fuel burn increases."

Qantas's Strambi concurs: "The A380 has met or exceeded all the original performance, noise and fuel burn guarantees made by Airbus at the time the aircraft purchase decision was made."

Clark says that because of the "favourable mach bias, there's quite a marked increase in terms in fuel reduction as you increase the cruise speed to Mach 0.85".

© H. Gousse/Airbus



Emirates' GP7200s have also behaved well during their first year in service, showing what Clark believes is an unprecedented "zero degradation" in performance. The airline has had two precautionary in-flight shutdowns, but neither was caused by the machinery, says Clark. "They were indication issues."

With two airlines operating a fleet of 14 Trent 900-powered A380s, the R-R fleet has accumulated significantly higher utilisation than the GP7200 to date - more than 225,000h against 81,400h.

Sirisena says that SIA's Trent 900s have suffered "some teething issues" and the fleet has undergone "a lot of engine changes to address early signs of potential problems. Rather than let the problem develop, Airbus and R-R have taken preventative action."

SIA has suffered three in-flight shutdowns, one of which was caused by fuel starvation and one by a quality/installation problem that caused an oil line to crack. The third incident, which occurred in September, was a precautionary shutdown after the crew received a warning and is still under investigation.

SIA Trent 900s have undergone a series of upgrades with changes including solenoid valves, electronic controls, bleed valves, fuel meeting valve units and wiring connectors, while high-pressure nozzle guide vanes have been replaced to address premature burning, says Sirisena. The latter issue resulted in the A380's first airworthiness directive.

MAINTENANCE INSPECTION

Meanwhile, SIA's oldest A380 (MSN003/9V-SKA) underwent the first C check maintenance inspection in September, having accumulated more than 8,000h and 1,000 cycles. The inspection, which has a two-year interval, was undertaken at the airline's Changi base with a "small army of Airbus people in attendance - about 100 folks", says Williams.

"We did some deeper inspections than we'd normally do in a C check and discovered some small things for us to follow up, but there were no major issues," he adds.

The aircraft was brought up to the latest modification standard in parallel with the inspection. As part of the inspection, Sirisena says that the airframe was giving "a health check, we were looking to see if there was the potential for rubbing" that may not have been identified during ground- and flight-testing.

A380 Cabin
 


"When you fly with a full passenger load there are different vibratory stresses than during flight-testing. Once an aircraft is in the air things flex, twist and turn, alignments are different and there are vibrations, stresses."

VIBRATIONS

This phenomenon has already seen some "transitory vibrations" identified in the plumbing for the A380's 345bar (5,000lb/in2) hydraulic system, Sirisena says. "We've seen some strange movement in the plumbing."

However, Williams says that Airbus "has not seen vibration as being an issue that has come up".

 

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