An airline stuns passengers by asking for £20,000 to complete the final leg of their journey to the UK. The demand was "unusual to say the least", the Civil Aviation Authority tells Channel 4 News.
The plane, returning from Amritsar in India to Birmingham and carrying around 180 passengers, had already been delayed by several days.
But when it stopped in Vienna to re-fuel, passengers were stunned when they were told they had to hand over around £20,000 to fund the final leg of the trip.
They say they were told the airline, Comtel Air "ran out of cash to fund the last leg of the trip".
Many refused to leave the plane but were told it would only return to Birmingham if the money was handed over. Passengers said they felt as if they were being "held to ransom".
Austrian police were called to the stand-off in Vienna, which ended when passengers were escorted to cash machines to draw out the money. Many had to borrow from each other to reach the sum total.
It's absolutely disgusting. There are still people stuck out there. Dalvinder Batra, relative of passenger
Gurhej Kaur, a blind 80-year-old from Handsworth Wood, was one of the passengers who spent more than 15 hours on the plane while her medication was in the hold.
Her 34-year-old relative, Dalvinder Batra, from Oldbury, told the Birmingham Mail: "It is absolutely disgusting. There are still people stuck out there. We have been told that the company has gone bust."
Reports suggest that up to 600 people on four different flights have been caught up in the fiasco.
Channel 4 News understands that a plane-load of passengers are still stuck in India.
Comtel Air, which has a strapline of "Vienna Executive Aviation", was unavailable for comment, with emails bouncing back and phones disconnected.
In a statement, the Foreign Office said: "We are aware that a number of British nationals have been affected by difficulties with Comtel airlines flights from Amritsar to Birmingham via Vienna.
"We have, and remain, in touch with the relevant authorities including the airline for clarification on how British nationals due to fly in the coming days will be affected. Our current advice to anyone affected is to contact their tour operator, travel agent or the airline for further information and about possible alternative arrangements. We would also advise that they monitor our travel advice for India for any updates.
"We took a number of calls from distressed British nationals in relation to this issue and we have provided consular assistance to those who have sought it."
Advice for passengers
Comtel Air operates from Birmingham Airport on Fridays, Saturdays and Sundays under normal circumstances. A spokesman told Channel 4 News it understood that Comtel was trying to get other passengers home but it was still "unsure" of future movements.
"It's not a great situation for anyone and we feel sorry for the passengers stuck," he said.
"Our advice at the moment is, if anyone is concerned, they should check with their tour operator or travel agent and check they are covered for compensation [by the Air Travel Organisers' Licensing scheme, Atol, a Civil Aviation Authority mechanism to protect air travellers]."
A spokesman for the Civil Aviation Authority (CAA) told Channel 4 News that the situation was "unusual to say the least".
It's not a great situation for anyone and we feel sorry for the passengers stuck. Birmingham Airport spokesman
He added: "We don't know the exact circumstances but it seems very unusual to say the least. Passengers have to be aware when they buy tickets of where they will finish - there has to be transparency over where they are going.
"Operators can't at a later stage demand money to continue the journey. There are laws protecting that kind of thing. Passengers do have rights and the laws are the same throughout the EU. We are trying to look into it."
Protection for travellers?
However the Association of British Travel Agents (Abta) told Channel 4 News the situation brought an issue to the fore which it had campaigned about for some time.
If people buy tickets on a scheduled airline, the airlines don't have to and don't provide any financial protection. So if there are any problems with getting the passengers to a destination, passengers then have to buy their own ticket and make their own way to their destination.
"This is an anomaly and it is unacceptable," an Abta spokesman said, particularly as the majority of flights are scheduled.
However, if passengers buy tickets for a chartered flight, someone has to have chartered that plane, such as a tour operator. Usually, the passenger will have bought their ticket from that tour operator and the tour operator will be responsible for getting them to their destination.
In the case of Comtel, it is unclear how the passengers booked their tickets. Travel agencies connected to the airline were unavailable for comment.