MINNEAPOLIS (AP) — Three months before a superjumbo jet engine blew apart and forced an emergency landing, European safety regulators had relaxed their inspection order for the same section of the engine implicated in the dangerous mishap.
In January, the European Aviation Safety Agency required airlines to inspect for wear on the shaft that holds one of the Rolls-Royce Trent 900 engine's turbine discs. The more wear they found, the sooner future inspections would be required.
In August, after Rolls-Royce had inspected several engines, EASA revised its directive. Previously, airlines had to calculate how worn out the part was based on the worst spot. Under the revised directive they calculate the average wear over the entire part.
And previously they had to assume the part was wearing out at a worst-case rate. The new rule allows them to calculate the wear rate on each engine. That meant less frequent inspections, which the revised directive said were "sufficient to prevent unacceptable wear."
The European directives warned of the potential for "in-flight shut down, oil migration and oil fire." The U.S. Federal Aviation Administration went further in adopting a version of the European directive in September, warning of an "uncontained failure of the engine, and damage to the airplane."
Some of the parts inside jet engines rotate faster than the speed of sound. Engines are designed so that even if part of one shatters, pieces of metal aren't sent rocketing away from the engine. An "uncontained engine failure" with shrapnel-like engine pieces that can damage other parts of the plane is both rare and extremely dangerous.
That's what happened Nov. 4. Investigators have said that leaking oil caused a fire in the engine of a Qantas A380 that heated metal parts and made the motor disintegrate over Indonesia last week before the jetliner returned safely to Singapore. Experts say the mishap damaged vital systems on the plane, which had been bound for Sydney.
The safety order wasn't addressing the exact same problem that caused the Qantas engine to disintegrate, but is very similar and involved a turbine next to the one that broke apart, said Chuck Eastlake, a former professor of aerospace engineering at Embry-Riddle University in Daytona Beach, Fla.
The decision to relax the EASA order was likely based on inspections that gave engineers confidence that the wear on parts that could cause an oil leak was predictable enough to allow more time to elapse, Eastlake said. In hindsight that appears not to have been the case, he said.
"That kind of stuff is always a judgment call based on experience," Eastlake said. "It's hard to specifically justify a decision like that because it isn't a matter of plugging numbers into a calculator and out comes an answer."
John Cox, an aviation safety consultant and former airline pilot, said it's a question of balancing "what is reasonable to ask the airlines to do against safety."
"The problem is we had a catastrophic failure. It turned out that apparently at least one engine had substantial wear that inspections didn't pick up," he said in a telephone interview from London.
No one from EASA was available to talk about the directive late Friday.
The agency usually takes the lead in issuing safety orders involving aircraft, engines and other equipment made by European manufacturers, just as the FAA does in cases that involve U.S. manufacturers.
Qantas spokesman Tom Woodward said Qantas has complied with all safety orders.
Rolls-Royce Group PLC said in an update to investors Friday that the Qantas engine incident last week was due to failure in a specific component that caused an engine fire and "the release of the intermediate pressure turbine disc." The company will be replacing the relevant part "according to an agreed program" as inspections on the engine continue in association with aviation regulators, it said. The company did not provide details.
The disc, a plate that holds the turbine blades that move air through the motor, broke apart in last week's mishap.
Three airlines — Qantas, Singapore and Lufthansa — fly the 20 A380s that use Trent 900 engines. Qantas and Singapore have grounded several of those after each found oil leaks on three engines.
Lufthansa spokesman Thomas Jachnow said the German airline has been told "that Rolls-Royce will gradually replace a modular part of the engine on all Trent 900 engines." He added that the "exact parts to be replaced haven't been finalized yet."
Airbus Chief Operating Officer John Leahy told reporters in Sydney that new versions of the Trent 900 engine that powers the Airbus A380 superjumbo will not suffer from the oil leaks that appear to have caused the fire on the Qantas flight. He said Rolls-Royce was equipping Trent 900s with software that would shut down a motor with leaking oil before it was put at risk of disintegration.
Airbus said it planned to take newer versions of the Trent engine off its A380 production line and ship them to Qantas so that the airline could change the engines on some of its superjumbos.
"We think the engines on the production line will be fine," The Age newspaper of Melbourne, Australia, quoted Leahy as saying. "The new engines should not have that issue ... in terms of this one part that seems to have had a problem with leaking oil."
The Herald Sun of Melbourne reported that Leahy said Rolls-Royce had made changes to some versions of engine to prevent such problems before the Nov. 4 mishap, but Airbus spokesman Justin Dubon denied the report. He said Leahy was referring to changes to the engines being made in light of the mishap.
Leahy, when asked whether he was suggesting that Rolls-Royce knew about problems with the engines before the Qantas incident, said, "Absolutely not," according to Dubon.
Dubon would not comment on whether changes had been made before the Qantas engine disintegrated, or whether the software Leahy described would be installed on engines already in service, referring those questions to Rolls-Royce. Rolls-Royce and the EASA declined repeated requests to comment about Leahy's remarks.
A mechanic who works for an airline that uses the engine told The Associated Press, however, that Rolls-Royce made modifications to the oil lubrication system on Trent 900s delivered starting in the second half of 2009. The mechanic spoke on condition of anonymity because he was not permitted to speak to the media.
The Qantas flight whose engine blew apart came into service in 2007.
Before last week's disintegration there were four malfunctions involving Trent 900 engines dating to 2008, three of which centered on the turbines or oil system. All the planes landed safely.
Two of the malfunctions led to EASA warnings, including the directive issued in January and revised in August.
There are three turbines in the Trent 900 engine. The EASA order said wear had been found on parts in the intermediate turbine that could cause an oil leak. The order warned that oil leaking from the intermediate turbine could cause a fire under the adjacent lower turbine, causing the disc in that turbine to fail. Instead, there was an oil fire in the Qantas plane, but it was the intermediate turbine disc that failed. The two turbines are just a few inches apart, said Eastlake, the former aerospace engineering professor.
London-based Rolls-Royce said in an update to investors Friday that the incident will cause full year profit growth "to be slightly lower than previously guided," but it also said that the company's other operations will help to offset any losses.
Shares in the company rose after the update — a signal that investors are happy to see a definitive statement after days of silence from the world's second-biggest engine maker behind General Electric.
____
Lowy reported from Washington. AP Aviation Writer Slobodan Lekic in Brussels and Associated Press writer Michael Weissenstein in London contributed to this report.
