A QANTAS Boeing 747 aircraft landed in Singapore on Friday morning with an engine-access panel missing, in the latest of a string of embarrassing incidents to hit the Australian carrier.

The panel, used to reach various parts of the engine, was found missing during a routine inspection. It was replaced and the flight continued to London following a six-hour delay.

A Qantas spokesman gave the assurance that the incident had 'absolutely no flight safety implications'.

The point was echoed by Australia's Civil Aviation Safety Authority.

Its spokesman Peter Gibson was reported by Associated Press wire agency as having said that planes are not affected when the panels come off.

It is 'quite legal' to continue flying without them, he said, adding that the force of air can sometimes detach the panels that have not been latched on firmly enough.

Qantas has been hit by bad press since late last month, when a B747 jumbo was forced into an emergency landing in the Philippines by a rupture in its fuselage.

Preliminary checks suggested that an exploding oxygen bottle may have been the cause.

Following that, another Qantas jet had to return to Adelaide because of an issue with its landing gear, and a Boeing 767 had to head back to Sydney soon after take-off with fluid oozing from a wing.

Meanwhile, Singapore Airlines has done a thorough inspection of all oxygen bottles on its 15 B747s and found everything in order.

The self-initiated checks on the oxygen bottles and surrounding brackets took about a week to complete, spokesman Stephen Forshaw told The Straits Times on Friday.

While it is wrong to assume that older jets are less safe, experts say they do have to be put through more regular and rigorous checks and maintenance.

SIA's oldest B747 is about 12 years old, twice the airline's average fleet age of six years.

With the arrival of the Airbus 380 superjumbo, the Singapore carrier is phasing out its B747s in two to three years.