ENGINEERS say an intermediate pressure turbine disc in the No 2 engine of QF32 failed, triggering the explosion that ripped through the engine casing of the A380.....
Investigators do not yet know why the disc failed, as the superjumbo carrying 440 passengers and 26 crew climbed after leaving Changi Airport in Singapore on Thursday. But they are examining certain scenarios that could have caused the problem. These include an oil fire in the bearing compartment, blocked cooling tubes or a bearing failure.
A less likely cause was a problem with a rectangular part at the root of the turbine blades known as the intermediate pressure (IP) turbine blade platform. An oil fire or bearing failure could cause the intermediate turbine shaft to sever, causing the IP turbine to rotate at twice the normal speed and, potentially, the disc to disintegrate....
This type of so-called "overspeed" is thought to have been responsible for a previous Qantas uncontained engine failure three months ago near San Francisco on a Boeing 747, with an RB-211 Rolls-Royce engine.
In that case, however, only the blades separated and the disc remained intact.
The explosion on QF32 was the third technical problem recorded with a Rolls-Royce Trent 900 engine and an A380 jet.
Two months ago, a Lufthansa superjumbo shut down one of its Trent 900 engines before landing at Frankfurt because of changes in oil pressure.
A Singapore Airlines A380 turned back after leaving Paris in September last year because of a Trent 900 engine malfunction.
The QF32 incident was the most severe of the three and quickly became known as the first catastrophic failure of the Rolls-Royce Trent 900 engine, which is installed on 20 of the 37 A380s currently operated by commercial airlines. Qantas immediately grounded its fleet of six A380s ahead of a major investigation.
The explosion on Thursday was powerful enough to overwhelm devices ringing the engine aimed at stopping or limiting rare uncontained failures, believed to account for just a few per cent of engine failures.
Normally these devices, made from kevlar and composites, help keep broken parts within the engine or force them to be expelled through the tail pipe.
As QF32 made its climb out of Singapore, the engines would not have been under maximum stress, even though they were in a higher energy phase of flight - the shorter hop from Singapore to Sydney meant the take-off would have been "de-rated" with thrust reduced by up to 25 per cent.
A senior A380 captain told The Weekend Australian that at 6000ft, the crew would have switched to climb thrust, which, under certain conditions, can be higher on an A380 than take-off thrust. However, it would have been well below the maximum.
The bang and the vibration of the uncontained failure and the shudders that followed would have alerted the flight crew to the engine problem.
They would probably have had a fire alarm and an engine failure warning in the flight deck followed by the cascading series of messages as hydraulics, generators and other systems failed in the engine. The flight crew would have launched into a detailed checklist aimed at assessing the damage to the engine.
The captain would have taken control of the aircraft and asked for the deluge of electronic centralised aircraft monitor (ECAM) messages to be read out by the support pilot. They would have identified the failed engine, closed the thrust lever, confirmed this had worked, and then shut the fuel control switch.
"If it's severe damage, you pull the engine fire switch, which is in the roof, and that will cut off all the hydraulics and fuel and electrics to the engine," the A380 captain said. "And normally if it's severe damage, you fire the first of the two fire bottles into the engine as a precautionary measure, even if there's no fire."
On Thursday, the A380 would probably have been in cruise configuration at 6000ft and the crew would have levelled off and performed a status check as well as informed air traffic control there was a problem and talked to engineers at Qantas. In this case they declared a Pan-Pan, one step down from a mayday, dumped fuel to reduce the aircraft's weight - dropping from about 140-150 tonnes of fuel to 80 tonnes - and landed the plane safely.
The A380 captain said passengers were unlikely to have noticed any difference in handling after the event, even with damage to the wing. "It's such a big airplane you'd be lucky to notice it," he said, noting that the pilots would trim the plane and set the autopilot to compensate for yaw (side-to-side) forces caused by only one engine working on one wing while two were operating on the other.
However, the plane's problems did not end after it had safely landed. Once on the ground, and before passengers could disembark,
the pilots found that damage to wiring in the wing meant they were unable to shut down the No 1 engine. Firefighters doused it with foam to shut it off, adding to the overall damage cost. (вот почему пенили 1-й как видно на видео)
The problem for Rolls-Royce and Qantas staff was that they could not be sure which of various scenarios was to blame.
They are conducting a series of inspections that would cover them all:: looking at oil monitoring for the past 50 sectors to pick up oil-feed problems; using a boroscope to check turbine blade platforms.
http://www.theaustralian.com.au/new...-superjumbo-down/story-e6frg6nf-1225948586541
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........"We know that the dramatic increase in the number of safety incidents involving Qantas jets coincides with an increase in the amount of work that is no longer carried out in-house," he said in a statement.
In the past 10 years, Qantas has shut down every in-house engine shop in Australia, he said, leading to a reduction in safety standards.
Heavy maintenance checks - which occur over the lifetime of the aircraft - on the A380s are carried out in Germany, while other maintenance has been increasingly outsourced to Singapore and Hong Kong, the association says.
"We have seen some
pretty horrid results of maintenance from the overseas facilities - things that aren't reported in the press," he said.
"
A bigger (incident) we have seen of late is, last year they had three engines on a 747 that weren't bolted correctly to the wings and they flew ... this aircraft for a month or so after a maintenance check in Hong Kong."
http://www.news.com.au/breaking-news/qantas-engineers-want-full-probe/story-e6frfku0-1225948024949
