Travel conditions have improved at some UK airports, but many passengers remain stranded.
Flights are now arriving and departing at most airports, but some aircraft and crew are still in the wrong places, resulting in continued delays and cancellations.
British Airways (BA) is asking passengers due to fly between now and December 24 to consider whether their travel is essential.
People who do not need to travel can cancel their flights and get a refund, or change their flights for another date in the next 355 days.
Heathrow airport is still only operating a severely reduced flight schedule, and pictures of stranded passengers continue to dominate the media.
BAA has admitted the airport may not return to normal operations until after Christmas.
Today, Heathrow published a list of flights that are likely to operate today, and has warned passengers not to travel to the airport unless their airline has confirmed their flight will depart.
Flights at London City, Gatwick, Edinburgh and Southampton airports are returning to normal, although the knock-on effects of earlier delays are still being felt.