Operators of Rolls-Royce Trent 900 engines will no longer be required to carry out repeated inspections of certain engine parts that were mandated by Europe's safety regulator after last November's uncontained engine failure on a Qantas Airways A380.
The European Aviation Safety Agency (EASA) has cancelled the most recent airworthiness directive it issued on 21 December 2010, which listed the requirements for operators to inspect the high pressure / intermediate pressure (HP/IP) structure of Trent 900s.
An uncontained failure of a Trent 900 on a Qantas A380 on 4 November had prompted the EASA to issue the airworthiness directives, which called on operators to carry out repeated inspections of their engines' low pressure turbine case drain, HP/IP structure air buffer cavity and oil service tubes to check for abnormal oil leakage.
Investigations into the Qantas incident have showed that the engine failure was a result of thinning in an oil feed tube, which led to an oil leak and fire. The thinning was introduced during the manufacturing process.
Since the last airworthiness directive issued on 21 December, the EASA says "the latest progress of the ongoing investigation, further assessment of manufacturing data and additional stress analysis continue to support the above failure scenario".
"In addition, all HP/IP structures containing an oil feed tube with a wall section below a certain threshold, and therefore having a potential risk of fracture, have been removed from service," it adds.
Inspections so far have not identified other engines that are at risk to "develop a failure scenario similar to the uncontained engine failure event", says the EASA.
The safety regulator adds that the inspections are "intrusive" and "introduce some risk from possible maintenance errors".
"The root cause of the incident having been addressed through other adequate measures, it is considered prudent to cancel these inspections," says the EASA.