The European Aviation Safety Agency (EASA) Dec. 21 ordered inspections of Roll-Royce (R-R) Trent 900s after an oil pump system failure traced to an improperly installed part disrupted a customer acceptance flight.

The problem triggered a low-pressure warning during the customer acceptance flight departure, EASA reports. The crew aborted the takeoff and returned to the gate without further incident.

Investigators discovered that the affected engine suffered a failed oil pump shear neck. Further investigation pinpointed a failed piston ring seal installed on the intermediate pressure (IP) compressor rear stub shaft (ICP RSS). Pieces of the seal were recovered from the internal gear box (IGB) rear scavenge screen and “smaller pieces” were found on the electrical magnetic chip detector, says EASA.

EASA’s directive, effective Dec. 28, requires one-time inspections to confirm that the piston rings are installed correctly. Engines with incorrectly installed rings must be removed and replaced with serviceable engines, says EASA.

The checks must be done within 50-200 engine flight cycles, depending on how many affected engines are installed on an airframe. Aircraft with four affected engines must be checked soonest.

The piston ring was introduced as part of a R-R modification that incorporated a modified spline IP turbine shaft, IPC RSS and coupling assembly, EASA says. The directive does not detail how many in-service engines have the modification and are therefore covered by the inspection order.

R-R issued service recommendations detailing the problem and recommending the inspections earlier this week. EASA notes that the one-time checks are an interim step while R-R and the regulator work on a terminating action.