By Tim Hepher, Rishav Chatterjee and Sneha Kumar
(Reuters) - European regulators have pinpointed a potentially flawed cleaning process during maintenance as investigators probe an engine fire that caused a Cathay Pacific Airbus jet carrying 348 people to turn back to base.
The European Union Aviation Safety Agency said on Thursday it was asking airlines to check the engines of more Airbus A350 jets but downgraded its response to the Sept. 2 incident, easing pressure on engine-maker Rolls-Royce (OTC:RYCEY).
The Airbus A350-1000 and its XWB-97 engines have been under scrutiny since the crew of a Zurich-bound flight detected an engine fire and extinguished it before dumping fuel and returning to Hong Kong, where it landed safely. The incident resulted in the grounding of a number of other Cathay flights.
Hong Kong's Air Accident Investigation Authority said on Thursday it had found a ruptured fuel hose in the jet's No. 2 engine, with five secondary hoses also showing signs of wear and tear. It said it had not yet identified the root cause.
"This serious incident illustrates the potential for fuel leaks through the ruptured secondary fuel manifold hose, which could result in engine fires," the AAIA said in a report.
Its report, unexpectedly released two weeks before the deadline for such initial summaries, started a rare exchange of contrasting safety announcements with European regulators.
The Hong Kong agency said the ongoing investigation would range from design to production, installation and maintenance and suggested the incident could have been much worse.
"If not promptly detected and addressed, this situation, along with further failures, could escalate into a more serious engine fire, potentially causing extensive damage to the aircraft," the report said.
But EASA, updating its own guidance several hours later, focused on the way such engines are maintained and called for checks on all A350 jets - including the more popular A350-900 - that have had at least two repair visits. It also downgraded its directive by dropping its previous "emergency" status, meaning it is less concerned about an immediate safety risk.
Previously it had only ordered checks on A350-1000 engines.
"In-service and in-shop inspections since then have identified that a specific cleaning process available during engine refurbishment may lead to fuel manifold main fuel hose degradation", EASA said.
One person familiar with the probe said the wrong type of cleaning product may have been used in at least one repair plant.
The checks are designed to find whether other engines may have been damaged in this way. So far only Cathay has confirmed it found some fuel-line damage on other jets, though Malaysia Airlines said it found and solved a potential problem.
SAFETY MICROSCOPE
The aborted flight triggered global headlines at a time when air safety is under the microscope and the engine industry is reeling from a string of industrial problems.
Shares in Rolls-Royce fell sharply after the initial incident but have recovered and gained 5% on Thursday.
Even before EASA's intervention, analysts said concerns about further engine-industry upheaval had eased.
"Combined with the lack of defective parts found in the fleet thus far, we believe that the issue implies minimal cost (or) disruption to all parties," Jefferies analyst Chloe Lemarie said.
The incident highlights the narrow margin for error in modern advanced jet engines, coupled with the importance of onboard systems that extinguished the fire in less than a minute.
The ruptured part links a manifold, where fuel arrives, to one of about 20 nozzles that spray fuel into a combustor to be ignited and turned into hot gas providing part of the thrust of the huge engine, the largest of its kind made in Europe.
Reuters first reported shortly after the incident that the engine's fuel-nozzle system was at the centre of the probe, rather than a more critical rotating part, and Bloomberg News reported that scrutiny focused on the nozzle's steel-braided fuel line.
Regulators did not say who carried out maintenance. Engine-makers frequently conduct maintenance themselves and Rolls-Royce has a specialist network for handling the Trent XWB.
Rolls had no immediate comment on repair networks but said airlines would check a "limited number" of A350-900 engines.
"Inspections of our Trent XWB-97 engines have progressed well, and we are confident we can continue at this pace, working closely with our supply chain to maintain minimal disruption,” the company said.
Cathay said it had complied with EASA inspections and added the fuel pipe was the first component of its type to suffer such a failure on an A350.
Airbus said it was working with Rolls-Royce and airlines on EASA's updated guidance.