Two of the three main Trent 900 operators, Singapore Airlines (SIA) and Lufthansa, turned up no findings on the engines of their Airbus A380 fleets, after the European Aviation Safety Agency (EASA) issued and airworthiness directive (AD) for engine checks last week.

The moves were caused by a fault in one engine on a SIA A380 flight from Singapore to Hongkong in July. At the time, pilots noticed a high intermediate-pressure vibration fault and fluctuating engine parameters, including low-pressure faults. They decided to throttle back the engine and turn back to Singapore. There were no issues with the other engines.

Both SIA and Lufthansa, which operate two of the three largest Trent 900 A380s fleets, have completed checks on all of their aircraft. Singapore Airlines has 18 A380s in service, Lufthansa has 10. Qantas—operating 12 aircraft of the type—could not be reached for comment immediately on Friday.

According to EASA, the spherical seat between the oil transfer tube and the end cover of the low-pressure turbine bearing housing was missing, and the agency assumes that it simply has not been installed on the particular engine. Because of the fault, the low-pressure system seized up. EASA said that the missing part caused the fracture of the oil tube and led to reduced oil flow and damage to the low-pressure and intermediate-pressure bearings. Rolls-Royce has indicated to EASA that other Trent 900 could potentially be affected, and the safety agency said the fault could lead to an uncontained engine failure.

The AD requires checks within as few as 20 engine cycles.

Of the A380 operators, Singapore Airlines, Lufthansa, Malaysia Airlines, China Southern and Qantas Airways are affected. Other airlines have equipped their A380s with Engine Alliance GP7200 engines.

The problems are unrelated to the November 2010 uncontained engine failure of Qantas Flight 32 in Singapore. At the time, the aircraft had to return to Singapore after engine debris caused severe damage mainly to the wing. The affected aircraft has only recently been repaired.