Mid-air mechanical issues forced back two Qantas flights after they left Sydney this afternoon, with one forced to dump fuel over the ocean before landing.
Flight QF7 to Dallas turned around after experiencing a mechanical issue, Qantas said.
The flaps on the Airbus A380 were unable to retract, which meant the plane could not fly efficiently, a statement from the airline said.
As the Dallas route is the longest in the Qantas network, the captain made the decision to turn around and return to Sydney.
The plane circled for 35 minutes and had to dump fuel east of Wollongong but has now landed in Sydney and will undergo inspections by engineers.
Another flight, QF63 to Johannesburg, returned to Sydney this afternoon due to a cracked pane of glass on the windscreen.
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 flight was safe to continue to Johannesburg but the captain made the decision to return to Sydney as the windscreen will be replaced there at Qantas' engineering base.
The aircraft, a Boeing 747-400, landed safely.
Qantas said it was working to accommodate affected passengers or offer them transport home before replacement services were organised.
Rebecca Cushway, who was on board flight QF7 to Dallas, said passengers were told the plane could only reach 5,000 feet after take off.
She said she felt nervous.
"But when they said we were safe and kept reassuring us that we could land safely, it was fine," she said.
Two Qantas faults in one day just a coincidence
Chair of the aviation department at Swinburne University, Stephen Frankhauser, said the fact these two incidents happened on the same day was unusual but merely a "statistical blip".
"At no point were the aircraft or the people in the aircraft in any danger," he said.
Mr Frankhauser explained that the wing flaps, which malfunctioned on the QF7, enable the plane to get more lift at slower speeds.
"Due to mechanical problems they weren't able to retract the flaps and that limited the speed of the airplane, and also the extra drag would mean the fuel burn would be such that you could not operate the plane over the [intended] distance."
He said cracked windscreens did not happen often but could limit the pressure the plane could withstand and the altitude at which it could fly.
Mr Frankhauser said it needed to be remembered that planes were mechanical systems and had a probability of failure.
"Usually what we hope is that that probability is very low... but it's not a probability of absolutely zero."
