Washington, Nov 7 (AP) US airlines began cancelling hundreds of flights on Thursday due to the Federal Aviation Administration's order to reduce traffic at the country's busiest airports starting Friday because of the ongoing government shutdown.

Close to 500 flights scheduled for Friday were already cut nationwide, and the number of cancellations climbed steadily throughout Thursday afternoon, according to FlightAware, a website that tracks flight disruptions.

The FAA order to cut flights at 40 of the busiest airports across the US includes New York, Los Angeles and Chicago, but the impact will disrupt travel at many smaller airports, too.

The FAA seeks to reduce service by 10 per cent across “high-volume” markets to maintain travel safety as air traffic controllers exhibit signs of strain during the shutdown. The move also comes as the Trump administration is ramping up pressure on Democrats in Congress to end the shutdown.

Airlines will phase in the 10 per cent reduction in their flight schedules at the airports across more than two dozen states. Just hours before the reductions went into place, airlines were scrambling to figure out where to cut and some travellers began changing or cancelling itineraries preemptively.

Travellers with plans for the weekend and beyond waited nervously to see if their flights would take off as scheduled.

The affected airports include busy connecting hubs and those in popular tourist destinations, including Atlanta, Denver, Orlando, Miami, and San Francisco. In some of the biggest cities -- such as Dallas, Houston and Chicago -- multiple airports will be affected.

Flight cuts will begin gradually ================== Airlines will phase in the cuts at the direction of the FAA, eliminating 4 per cent of flights at the 40 airports on Friday and working up to 10 per cent, according to three people familiar with the plans who were not authorised to discuss them publicly.

United Airlines will cut 4 per cent of its flights over the weekend based on FAA guidance, company spokesperson Josh Freed said.

The FAA had not yet published an official order as of Thursday afternoon and didn't immediately respond to questions about implementation details.

Some airlines plan to focus on slashing routes to and from small and medium-sized cities.

“This is going to have a noticeable impact across the US air transportation system,” industry analyst Henry Harteveldt said.

The flight reductions coming just weeks before the busy holiday season have travellers already changing their plans or looking at other options.

Fallon Carter cancelled her Friday flight from New York to Tampa, Florida, where she planned to spend the weekend at the beach. She was worried about making it back to Long Island for her best friend's wedding where she'll be a bridesmaid.

“I don't know if I get there, will I get home?” Carter said.

The FAA is imposing the reductions to relieve pressure on air traffic controllers who are working without pay during the shutdown and have been increasingly taking sick days.

Air traffic controllers have been working unpaid since the shutdown began October 1. Most work mandatory overtime six days a week, leaving little time for side jobs to help cover bills unless they call out.

The FAA in recent weeks delayed flights when airports or its other facilities were short on controllers.

Airlines shuffling schedules ================ Airlines said they would try to minimise impact on customers, some of whom will see weekend travel plans disrupted with little notice.

United, Delta Air Lines and American Airlines were among carriers that said they would offer refunds to passengers who opt not to fly, even if they purchased non-refundable tickets.

The head of Frontier Airlines recommended that travellers buy backup tickets with another airline to avoid being stranded.

The cuts could also disrupt package deliveries because two airports with major distribution centres are on the list -- FedEx operates at the airport in Memphis, Tennessee, and UPS in Louisville, Kentucky, the site of this week's deadly cargo plane crash.

The cuts could affect as many as 1,800 flights, or upward of 268,000 passengers, per day, according to an estimate by aviation analytics firm Cirium.

Airlines are used to dealing with cancelling thousands of flights on short notice during severe weather, but the difference now is that these cuts during the shutdown will last indefinitely until safety data improves.

Shutdown already straining travel ===================== The shutdown is putting unnecessary strain on the system and damaging confidence in the US air travel experience, said US Travel Association President and CEO Geoff Freeman.

Kelly Matthews, who lives in Flat Rock, Michigan and frequently flies for work, said she has cancelled most of her upcoming trips and understands why federal airport employees have stopped showing up.

“You can't expect people to go into work when they're not getting a paycheck for the continuation of over a month now,” she said. “I mean, it's not a matter of them not wanting to do the job -- but you can't afford to pay for gas, your day care and everything else.” (AP) ARI