A Qantas plane that was sent to Azerbaijan to recover passengers after an emergency landing has finally left and is on its way to London on Christmas morning, but a string of challenges has hampered holiday plans for those onboard.

As relieved passengers lined up at the airport to board the flight that would take them to London on Sunday morning, the original Qantas plane that flew them there remained on the ground.

According to The Guardian, the manufacturer will be involved in investigations.

The passengers on the flight said they were relieved to be on their way after missing Christmas Eve.

After days of delays, the Brown family, who were travelling with their two small children to Julia's family in England for the holidays, were tired and hung on by a thread.

We're on our way out. We are grateful for the professionalism, empathy and care shown by our crew and so grateful for all the team that have flown in and sacrificed their own Christmas for us.

We made the most of it and made lots of new friends.

The lack of other staff in the city made it necessary for Qantas staff to fly to Baku to provide information to stranded passengers.

Many of the passengers on the initial flight didn't show up for the recovery flight. Several passengers bought new flights at their own expense in order to get to London in time for Christmas. Several people traveled via Istanbul.

The QF1 flight that was forced to make an emergency landing in Singapore on Friday is scheduled to land in London at 8am on Sunday.

Smoke was detected in the cargo hold as the plane flew over Georgian airspace, and the pilots reported a code used to communicate an emergency to air traffic controllers.

The A380 made a 180 degree turn and landed safely at the Heydar Aliyev airport, which has runways that are long enough to hold the superjumbo. There was no evidence of smoke when emergency crews met the aircraft.

The pilots were alert to the possibility of smoke in the cargo hold. Although it was thought to be a sensor fault, the aircraft diverted to Azerbaijan as a precautionary measure.

The initial response was hampered by the lack of ground staff and relief crew in the location.

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Passengers were ushered into the airport terminal, but pilots and aircrew were too tired to work on Friday. Water bottles and sandwiches were given to the people who were stranded.

Qantas staff in Australia began booking rooms for guests at an airport hotel when it became clear the plane couldn't be flown. Qantas staff in Australia had to manually apply for visas for passengers leaving the airport. Diplomatic staff became involved.

On Friday, a decision was made to send in engineers from London to help clear the plane, and by Saturday, Qantas announced it was sending a recovery plane.

Passengers were left without their luggage, which remained inside the hold of the plane as it was inspected by engineers, and airport workers were not trained to unload the aircraft.

The passengers were angry that the recovery flight would only take them to London on Christmas. The recovery plane had to negotiate airspace clearances on a direct route because Qantas doesn't operate in the area.

Due to restrictions on night-time operations at the airport, it was forced to wait until 5 am on Sunday to leave. Baggage was transferred from the initial plane to the recovery plane.

As investigators continue to examine the plane, the A380 will remain there.

Engineers have so far found no evidence of smoke in the cargo hold, but the assessments are continuing.