Sydney - A Qantas Airways jet aborted a flight to Singapore and returned to the Australian west coast city of Perth after one of its two engines was shut down, news reports said Saturday.

The Airbus A330 with 168 passengers aboard turned back Friday when an engine oil warning light flashed in the cockpit.

Aviation sources told The Sydney Morning Herald that the engine starter motor failed because maintenance engineers in Hong Kong had forgotten to oil the motor after an overhaul last week.

"Initial inspections by engineers indicate that the fault with the engine starter motor could have led to the engine oil problem," engineering general manager David Cox told the newspaper.

All Qantas A330s are serviced overseas, and this particular aircraft returned to Australia last week from a four-day service in Hong Kong.

Civil Aviation Safety Authority (CASA) spokesman Peter Gibson confirmed preliminary reports that the malfunction had originated in the starter motor and that the oil supply was being looked at.

"CASA has been kept fully informed on the incident by Qantas and will be closely monitoring Qantas' investigation of the event," Gibson said.

Recent maintenance-related problems at the airline include a Singapore-London flight terminating in the German city of Frankfurt after one of its engines had to be shut down.

A faulty rudder delayed a plane from London for 15 hours, and an internal flight was forced into an unscheduled landing because ground crew had forgotten to empty its toilet tanks.

Qantas, which has never lost an aircraft in an accident, has been severely embarrassed by the run of misfortune.