Thai Airways International has removed a second Rolls-Royce Trent 800 engine from one of its Boeing 777 aircraft in two months, after metal debris was again found on the magnetic chip-detector (MCD).

The second unscheduled removal by Thai of a Trent 800 occurred on 25 December, 1996, following a routine inspection of the engine's MCD. The engine is now at Bangkok's Don Muang Airport, awaiting shipment back to R-R in the UK for inspection.

Thai had already returned one engine to R-R, following a similar incident with the MCD in November. Metal was found during a check on the ground of the engine's accessory gearbox oil pump, following an earlier low oil pressure reading.

Attention in both cases is understood to focus on a suspected failure of a small bearing in the area of the radial drive to the accessory gearbox. The debris material found on the MCD and in the oil sump of the first engine is believed to be the same as that used for roller cage-type bearings.

Its unclear if the Trent 800 problem experienced by Thai is related to the bearing failure suffered by a Cathay Pacific Airways' Trent 700-powered Airbus A330 in November. That aircraft was forced to return to Saigon when the accessory gearbox failed and the engine shut-down (Flight International, 20-26 November, 1996).

R-R says that it is awaiting the return of the engine from Thai, and has not established a cause "-but there is no indication at the moment that the incidents are connected", it says.

Cathay subsequently removed its engine and returned it to Hong Kong for inspection, which revealed MCD contamination. Sources within Cathay and R-R have since confirmed that the gearbox failure was blamed on "a defective batch of bearings".

Although the Trent family has suffered a string of teething problems since entering service on the Airbus A330 and Boeing 777, solutions have been developed for the most of them.

Source: Flight International