Two Qantas long-haul aircraft carrying hundreds of passengers have been forced to return to Sydney after one suffered wing flap problems and the other a crack to the outer pane of a cockpit windscreen just hours into their flights.

A Boeing 747-400 jumbo – Qantas Flight 63 – on its way to Johannesburg in South Africa, departed Sydney just before 11am on Friday before the captain decided while above Tasmania to turn back to Sydney.

An A380 – QF7 – flying to Dallas in the United States, departed at 1.40pm and turned around shortly afterwards, circling off the coast of Wollongong as it dumped fuel.