SYDNEY - AUSTRALIA'S biggest airline Qantas was on Monday told to improve maintenance on its fleet after the national aviation watchdog examined the carrier following a series of mechanical problems.

The Civil Aviation Safety Authority (CASA) said it had found evidence of 'emerging problems' in maintenance procedures at Qantas and said the airline failed to meet some of its self-imposed standards.

But it said it had no doubt that Qantas was a safe airline, and there was no evidence of system failures in maintenance or engineering at the carrier.

'CASA wants Qantas to make a range of improvements to the way it manages and delivers aircraft maintenance,' it said in a statement.

The 'Flying Kangaroo' has been embarrassed by a series of recent incidents, the most serious a mid-air blast caused by an exploding oxygen bottle which blew a hole in the fuselage of a jet bound for Australia in July.

Days later, a Qantas airliner was forced to return to Adelaide after a landing gear door failed to retract. In August, another Qantas jet was forced to return to Sydney shortly after take off when the pilot detected a hydraulic leak in the wing.

On Sunday, the airline diverted a London-bound plane to Frankfurt after the pilot noticed an unusual vibration in one engine.

CASA's deputy chief executive officer of operations Mick Quinn said these incidents were unrelated, and that there had been no increase in the rate of safety incidents.

'We believe these are random events, the sort of events that would happen on any airline, on any given day, in any part of the world,' he said.

But he said CASA had 'looked carefully at the Qantas maintenance systems and performance and uncovered signs of emerging problems'.

'The review found maintenance performance within Qantas is showing some adverse trends and is now below the airline's own benchmarks.' -- AFP