The Australian Transport Safety Bureau (ATSB) said on Friday that its probe on the near-fatal engine breakdown of Qantas Airways' QF2 over Bangkok, Thailand in October 2011 still faces a blank wall.

In an update report that the ATSB has furnished, the agency has determined that the Rolls Royce engine number three fitted on Qantas' Boeing 747 failed when a single compressor blade that was located at the centre of whole engine structure broke and caused further damage with neighbouring components.

But what were left inside provided no clues for ATSB probers to pick up from, the report said.

"The condition of the blade fragments was such that identification and physical analysis of the blade release mechanism was not possible," the ATSB report was quoted by Fairfax as saying in explaining the magnitude of damages wrought by the turbine blade that suddenly snapped out of place.

It is understood that with such conditions, investigators would find it hard to determine the root cause of the engine failure that for a brief time had endangered the lives of 376 passengers and crew carried by Flight QF2.

According to media reports, the Qantas plane had just took off from Bangkok and was en route to Sydney on October 16 last year when it developed engine trouble, which passenger accounts said caused fumes to seep in though the aircraft's cabin area for a number of minutes.

Qantas pilots responded to the emergency by shutting down the troubled engine, turning around the plane and circling the Bangkok airspace for close to one hour while dumping tonnes of jet fuel prior to attempting a safe touch down at the Thai capital's airport.

No injuries were reported during the mid-air scare but it brought further attention on the state of Rolls Royce engines that were mostly installed on Boeing and Airbus planes that belong to the Qantas fleet.

The incident was preceded by another case in Indonesia, in which Qantas Flight QF32 suffered a blown out engine that forced pilots of the Airbus plane to head back to Jakarta.

The engine problem at that time, ensuing investigation showed, was prompted by an oil pipe that leaked, which led to a fire that engulfed the engine casing and its eventual explosion.

Yet for the QF2 case, the ATSB admitted that it is clueless on why the engine blade broke and set its failure.

The latest update from the agency suggested that it would rely on further findings that would come from Rolls Royce, hinting that "the engine manufacturer was continuing their internal investigation into the occurrence."

The ATSB report noted too that the subject engine has been found be at least 20,000 hours old in terms of the total flights that it has served.

The refurbished Rolls Royce engine was also credited with combined 2,000 take offs and landings prior to the Bangkok incident.

Initial submissions from Rolls Royce had indicated that an engine blade running amuck inside the engine casing was the first of such case for the English manufacturer.