SYDNEY: Two international Qantas flights suffered mid-air mechanical problems Friday and had to turn back to Sydney, with one unable to retract wing flaps and another suffering a cracked window pane, the Australian carrier said.

Flight QF7 was enroute to Dallas, but the Airbus A380´s captain decided to head back to Sydney after discovering the wing flaps could not be retracted.

"(This) means the aircraft can´t fly efficiently. As the Dallas flight is our longest on the network, the captain made the decision to return to Sydney," Qantas said in a statement.

The second flight, QF63 to Johannesburg, returned when "a cracked pane of glass on the aircraft windscreen" was found.

"An aircraft windscreen is made up of three layers of glass, the outer pane had cracked but did not compromise the integrity of the aircraft," the statement added.

"The aircraft was safe to continue to Johannesburg but the captain made the decision to return as the windscreen will be replaced at Qantas´ engineering base in Sydney."

Qantas said the Boeing 747-400 landed safely. Replacement flights were being arranged for passengers.

Several flights have had to return to Australia in recent months, including an AirAsia Gold Coast to Kuala Lumpur service last month that the carrier said involved a suspected bird strike.

In June, a China Eastern plane bound for Shanghai made an emergency landing in Sydney after a huge hole appeared in one of its engine casings.