Heavy snow in parts of Europe continues to cause disruption for Christmas travellers.
Frankfurt airport in Germany is open again on Tuesday, but Heathrow in London is operating at one-third capacity.
Passengers without confirmed bookings are being told not to turn up there before Christmas.
Gatwick airport in London was closed because of fresh snow, but has since reopened.
Charles de Gaulle airport in Paris is working around the clock to try to clear a backlog of delayed flights.
The BBC reports railways in Germany were also struggling to cope, as air travellers who could not get flights resorted to other means of transport.
The bad weather has made many roads dangerous. Eurostar says around 80% of trains between London, Paris and Brussels are operating.
The ABC reports Arctic weather conditions are expected to continue for the next few days.
Analysts believe the disruptions are costing British Airways about £65 million per day.
KLM-Air France said the weekend's disruption had cost it about 15 to 20 million euros.
The European Union says airports are a weak link in the continent's infrastructure. Transport commissioner Siim Kallas says they need to get serious about planning so they can operate more effectively in the future.