(CNN) -- The thousands of travelers who have been stuck at airports around the world because of the volcanic ash cloud over Europe will need more patience when airliners are cleared to fly.
The huge backlog of passengers combined with flights that are already full means they may not be going home anytime soon.
It could take three to six days for airline operations to get back to normal, said Giovanni Bisignani, the director general and CEO of the International Air Transport Association, on Monday.
The group represents 230 airlines all over the world and has been a vocal critic of how European governments have handled the crisis.
"Even if they opened European airspace tomorrow, the majority of passengers should not expect to get on the first flight out in the morning," added Steve Lott, the group's head of communications for North America.
"An international airline system is such a carefully orchestrated network that any disruption, especially of this size, is really going to take many days for operations to get back to normal."
Adding to the problem will be the passengers who are scheduled to fly on the dates when normal service resumes and who will have the priority to travel.
If airlines bump booked passengers in order to accommodate stranded ones, the bumped travelers would require hotel accommodations and would be entitled to compensation, said David Henderson, a spokesman for the Association of European Airlines.
"There would be very, very big bills doing that," Henderson said.
The scenario of booked passengers being kicked off to make room for stuck travelers when flights resume is unlikely. Those who have a confirmed seat are going to get on their flights, Lott said.
Airlines have several options to try to clear the backlog. Major carriers may have the flexibility to add more flights or put larger aircraft on regular routes, Lott said.
Delta, for example, is in the process of scheduling more flights so it can start getting passengers out as quickly as possible, spokesman Anthony Black said. He could not estimate how long it would take the airline to deliver its stuck passengers to their destinations.
Meanwhile, Germany's Lufthansa -- which has 27 planes on the ground in North America -- is hoping to add flights "as soon as we can," spokeswoman Jennifer Janzen said.
"The main priority now is to work with the aircraft that we currently have on the ground and all over the world and get those back into some sort of rotation," Janzen said. "This is worse than 9/11 for us."
Lufthansa is also focusing on the passengers who are in transit and have been stuck in North America for the past few days, Janzen added.
Meanwhile, air travelers are being urged to stay informed and plan on being stuck for a little while longer.
"I would say to any passenger stranded: Do not immediately rush to the airport because you believe your airline is back in the air," said CNN's Richard Quest, a business travel specialist who is himself stuck in New York.
"Check the Web sites, call the call centers and wait. ... You do know you will get home at some point."