As airlines idle thousands of aircraft for which there are no passengers, they are hitting an unprecedented problem: finding a place to park them. In the United States, United Airlines Holdings and American Airlines Group said they are parking planes at maintenance facilities for now, while Delta Air Lines said it was still looking into the issue.

FlightRadar24 data showed Delta had moved a dozen planes to Marana in mid-March and even more to Victorville over the last week.

Taxiways, maintenance hangars and even runways at major airports are being transformed into giant parking lots for more than 2,500 airliners, the biggest of which takes up about as much room as an eight-story building with a footprint 3/4 the size of an American football field.

The number of planes in storage has doubled to more than 5,000 since the start of the year, according to Cirium data, with more expected to be parked in the coming weeks as carriers like Australia’s Qantas Airways and Singapore Airlines Ltd proceed with further announced cuts to flight schedules. In Frankfurt, Germany’s biggest airport is a ghost town of silent airliners. Its northwest landing runway, including taxiways and bridges, has been converted to an aircraft parking lot for Lufthansa, Condor and other airlines. Lufthansa brand Swiss has rented parking spots at a military airport close to Zurich.

Similar crowds of planes are parked at other major airports, including Hong Kong, Seoul, Berlin and Vienna as well as traditional desert parking lots in Victorville, California, and Marana, Arizona, according to data from flight tracking website FlightRadar24.

Reuters