Qantas plane over Antarctica makes sudden U-turn four hours after takeoff - as hundreds of passengers are left stranded at LAX on Christmas after the airline cancelled flight to Melbourne

It is not turning out to be a particularly joyful Christmas period for Qantas after mechanical issues plagued three long-haul flights.   

Around 300 frustrated Qantas passengers were left stuck in Los Angeles after two aborted flights - causing them to miss spending Christmas Day in Australia despite being booked to fly to Melbourne last week.

In a separate incident on Christmas Day another Qantas flight to South Africa was suddenly turned around four-and-a-half hours into its flight as it neared to coast of Antarctica.

Emergency crews met the plane on the tarmac when it returned to Sydney Airport - where it had departed from - about nine hours later.

QF63, which is an Airbus A380, left Sydney for Johannesburg shortly before 10 am on December 25 but was back in Sydney by 7.30pm after suffering an unspecified mechanical issue. 

A Qantas spokesperson said the 'pilots followed normal procedures and returned to Sydney for the aircraft to be checked by engineers'.

'Customers will be reaccommodated on a service tomorrow morning and we want to thank them for their patience and understanding,' the spokesperson said.

There were no reported injuries. 

Meanwhile over in America, QF94 was scheduled to leave Los Angeles International Airport bound for Melbourne on December 22 at 8:30pm local time.

However, despite passengers boarding the plane shortly before the scheduled take-off time it sat idle on the runway for six hours, according to Perth-based sports podcaster Will Schofield. 

'Qantas boarded all customers and held them on the flight for 6 hours until eventually disembarking everyone at 2am,' Schofield tweeted on Tuesday.   

'Several passengers have been stranded at LAX for over 48 hours. 

'Qantas communication exceptionally poor, at this stage it still isn't clear how - 300 passengers will return to Aus. Christmas Eve and Christmas Day both missed.'

Schofield said the flight was rescheduled for 10.30pm on December 23 but again did not fly.  

'About 30 minutes prior to departure, Qantas once again cancelled the flight citing the same engineering issue,' Schofield tweeted.

'Qantas knew it wasn't going to fly. Texted passengers saying there was a 90 minute delay about 4 hours before. None of the crew came to the gate.'

 'SPIRIT OF AUSTRALIA?'

A Qantas spokesperson told Daily Mail Australia on Wednesday the Boeing 787 Dreamliner meant to fly on December 22 had suffered a hydraulic issue that engineers were unable to fix meaning a replacement plane had to be brought in.   

'We want to sincerely apologise to all customers impacted by the significant delay to our Los Angeles – Melbourne flight,' the spokesperson said.

'We understand how disappointing and frustrating this experience would have been, particularly for those who are missing Christmas Day with their loved ones. 

'We're reaching out to customers to offer compensation, and we want to thank them for their patience and understanding.'

It is understood Qantas offered accommodation, transfers, meal vouchers and a choice of either Frequent Flyer Points or a travel voucher as compensation to the passengers stuck in Los Angeles.

After eventually boarding a working plane the rescheduled customers are set to arrive in Melbourne tonight.