Sydney - Qantas Airways Ltd failed to meet its own maintenance performance targets, Australia's Civil Aviation Safety Authority (CASA) said Monday.

CASA decided to investigate the carrier after a run of technical hitches that saw an emergency landing, bits falling off planes and ground crew forgetting to empty toilet tanks.

"CASA has looked carefully at the Qantas maintenance systems and performance and uncovered signs of emerging problems," the authority said in a statement. "The review found maintenance performance within Qantas is showing some adverse trends and is now below the airline's own benchmarks."

Maintenance-related problems continued Sunday with a Singapore-London flight terminating in the German city of Frankfurt after one of the engines of a Boeing 747 developed a rattle and had to be shut down.

Last week 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.

Two weeks ago engineers in Singapore discovered a body panel had fallen off a Qantas jumbo jet flying in from Melbourne.

The worst scare came July 25 when an exploding oxygen cylinder forced a Qantas jet to make an emergency landing in Manila. The blast punched a 3-metre hole in the fuselage of the Boeing 747-400 flying from Hong Kong to Melbourne, forcing the pilot to descend from 29,000 feet to 10,000 feet in about five minutes and make an emergency landing in Manila.

One week after the Manila incident, a domestic flight was forced to return to Adelaide after a wheel bay door on a Boeing 767 failed to close properly.

Just days after that, a flight bound for Manila returned to Sydney after the pilot declared an emergency and dumped fuel because of a leak in the hydraulics operating a wing flap. (dpa)