The Federal Aviation Administration says it plans to reduce air traffic by 10% across 40 ‘high-volume’ markets beginning Friday morning to maintain safety during the ongoing government shutdown.

The Associated Press

Flight cancellations have begun at 40 United States airports, including those in New York, Chicago and Los Angeles, due to the continuing U.S. government shutdown.

The U.S. Federal Aviation Administration ordered a four per cent reduction in air traffic for Friday, ramping up to 10 per cent by next week. But Transportation Secretary Sean Duffy said that number could rise to 20 per cent if the shutdown continues.

The FAA is imposing the cuts – which could include up to 1,800 flights and about 268,000 seats – to take pressure off air traffic controllers. As federal employees, they have gone without pay during the 38-day shutdown, which has also led to more flight delays.

Travellers in limbo as U.S. shutdown-related flight cancellations take effect

While international flights are exempt, experts say the directive will certainly cause disruptions for Canadians travelling to, from or through the U.S, and potentially within Canada as well.

“This decision is going to affect passengers,” Western University employment relations professor Geraint Harvey told The Canadian Press.

Here’s a closer look at what to know about the cancellations and how they could impact Canadian passengers.

Which airports are affected by flight cancellations?

A list obtained by the Associated Press includes 40 airports with Atlanta, Denver, Dallas, Miami, Newark and San Francisco also among them. Here is the full list of all 40 airports:

John F. Kennedy International (New York)LaGuardia Airport (New York)Newark Liberty International (New Jersey)Teterboro (New Jersey)Boston Logan International (Massachusetts)Philadelphia International (Pennsylvania)Ronald Reagan Washington National (Virginia)Washington Dulles International (Virginia)Baltimore/Washington International (Maryland)Cincinnati/Northern Kentucky International (Ohio)Hartsfield-Jackson Atlanta International (Georgia)Dallas Love Field (Texas)Dallas/Fort Worth International (Texas)George Bush Houston Intercontinental (Texas)Houston Hobby (Texas)Charlotte Douglas International (North Carolina)Miami International (Florida)Fort Lauderdale/Hollywood International (Florida)Tampa International (Florida)Orlando International (Florida)Louisville International (Kentucky)Memphis International (Tennessee)Chicago O’Hare International (Illinois)Chicago Midway International (Illinois)Minneapolis/St Paul International (Minnesota)Detroit Metropolitan Wayne County (Michigan)Indianapolis International (Indiana)Los Angeles International (California)Oakland International (California)Ontario International (California)San Francisco International (California)San Diego International (California)Seattle/Tacoma International (Washington)Salt Lake City International (Utah)Anchorage International (Alaska)Denver International (Colorado)Phoenix Sky Harbor International (Arizona)Honolulu International (Hawaii)Harry Reid International Airport (Las Vegas, Nevada)Portland International (Oregon)Why is the U.S. government shutdown causing flight cancellations?Open this photo in gallery:

The FAA’s reduction is in part an effort to keep airspace safe amid staffing shortages due to the government shutdown.Brandon Bell/Getty Images

Air traffic controllers have gone without paycheques during the shutdown of the U.S. federal government. That’s led to controllers calling in sick and contributed to staffing shortages that have been affecting air travel for weeks.

Most controllers work mandatory overtime six days a week during the shutdown without pay, the National Air Traffic Controllers Association has said.

That leaves little time for a side job unless controllers call in sick to the FAA.

“If this shutdown doesn’t end relatively soon, the consequence is that more controllers don’t come to work,” the Transportation Secretary told Fox News on Friday. “I don’t want to see that.”

When will the U.S. flight cancellations begin and end?Open this photo in gallery:

The George Bush Intercontinental Airport in Houston, Texas is one of 40 being directed to reduce domestic flights by 10 per cent.Brandon Bell/Getty Images

Airlines began cancelling Friday flights on Thursday afternoon. Airlines have said people could see weekend travel plans disrupted with little notice.

More than 815 flights have been called off nationwide, according to FlightAware. Delta Air Lines said it would scratch roughly 170 flights Friday, and American Airlines planned to cut 220 daily through Monday.

Three percent of all U.S. flights scheduled for Friday — or 748 flights — had been canceled as of 6 a.m. ET, while about 1.7 per cent of Saturday’s flights had been canceled, according to aviation analytics firm Cirium.

The FAA said the reductions would start at 4 per cent and ramp up to 10 per cent by Nov. 14. They are to be in effect between 6 a.m. and 10 p.m. and impact all commercial airlines.

The CEO of United Airlines said Wednesday that long-haul international flying and hub-to-hub routes would not be impacted. Instead, it will cut regional and other domestic flights.

Why has the U.S. government shut down? Here’s what to know

It’s unclear when the reduced flights could end. Airlines, unions and the travel industry have urged U.S. Congress to end the shutdown, which on Wednesday became the longest on record.

U.S. Transportation Secretary Sean Duffy warned this week there could be chaos in the skies if the shutdown drags on long enough for controllers to miss their second full paycheck next week.

How could flight cancellations affect Canadian travellers?Open this photo in gallery:

An Air Canada commercial airliner takes-off from Los Angeles International Airport on Thursday. International flights are exempt from the cuts, but experts say they’ll likely still be impacted.Mike Blake/Reuters

International flights, including those between Canada and the U.S., are exempt from the FAA’s directive. However some Canadian passengers’ connecting flights within the United States are at risk of being cancelled.

When there is no direct flight to a passenger’s final U.S. destination, Canadian airlines offer connecting flights with American partner airlines. Air Canada and WestJet both partner with United Airlines, while WestJet’s other U.S. partners include Delta, American Airlines and Alaska Airlines.

A look of the departure boards at major Canadian airports on Friday afternoon showed a couple of cancellations and a handful of delays to U.S. cities but nothing out of the ordinary.

Vancouver International Airport says it doesn’t anticipate an immediate impact to flights or passengers, but that could change if the reductions continue.

“The integrated nature of how airlines use aircraft and crew does have the potential for knock-on effects to routes between Canada and the U.S. should this escalate,” airport spokesperson Reena Gacad Kirkpatrick said in an emailed statement to The Globe.

Montreal Trudeau International Airport “is fully operational, but of course, our teams are monitoring the situation closely, in collaboration with our partners,” spokesperson Émilie Chevrette told The Globe Thursday.

The Globe and Mail has also reached out to Toronto Pearson International for comment.

How are Canadian airlines responding?Open this photo in gallery:

Air Canada, WestJet and Porter flew 4,000 flights per week between the U.S. and Canada last month, including from YVR Vancouver International Airport.DARRYL DYCK/The Canadian Press

Canada’s two major airlines told The Globe their operations have not yet been affected but they are watching the situation closely, and preparing for a potential impact on flights and passengers.

Air Canada said it is maintaining its normal schedule but any passengers booked on connecting flights with United Airlines can rebook or defer their travel with no change fee.

WestJet has not been affected as of Friday afternoon, spokesperson Julia Brunet told The Globe in an emailed statement. On Thursday, Brunet said the airline is in close contact with its U.S. partners “will proactively manage our operations to minimize any potential disruptions going forward.”

For Porter Airlines, FAA staffing shortages have already caused delays in key markets south of the border. The airline is allowing free flight changes to some U.S. destinations until Monday, just in case.

“While we anticipate some disruptions due to FAA staffing shortages, this is currently being managed over the course of each day based on the circumstances,” Porter spokesperson Brad Cicero said in an emailed statement to The Globe on Friday.

Flair Airlines’ chief commercial officer Eric Tanner said Friday they are monitoring the situation closely.

Air Canada, WestJet and Porter flew 4,000 flights per week between the U.S. and Canada last month, according to figures from aviation data firm Cirium.

If you booked a connecting flight separately and not through a Canadian airline, United Airlines and Delta Air Lines both said they would offer refunds to travellers who opt not to fly, even if they have tickets that wouldn’t typically be eligible for refunds.

What should I do if I’m flying between Canada and the U.S.?Open this photo in gallery:

Canadian airlines and airports are advising passengers to check airline and airport websites for their latest flight information.Brandon Bell/Getty Images

The FAA has advised passengers to expect delays and check their flight status through their departing airport’s website.

Both Vancouver and Montreal’s airports also recommend Canadian travellers check their airline’s website or airport’s website to ensure they have the most up-to-date flight information, particularly if they are travelling to the U.S. or returning on a U.S. airline.

Has the FAA cancelled flights before?Open this photo in gallery:

People wait in line at a security checkpoint at the George Bush Intercontinental Airport, one of the 40 airports being affected by cuts.Brandon Bell/Getty Images

FAA Administrator Bryan Bedford said this week that he’s never seen these kinds of measures taken before in his nearly four-decade experience in the aviation field.

“We’re in new territory in terms of government shutdowns,” he said Wednesday.

Staffing problems led to delays throughout October, but they were mostly isolated and temporary. Last weekend, though, saw a change.

From Friday to Sunday evening, at least 39 air traffic control facilities reported potential staffing limits, according to an Associated Press analysis of operations plans shared through the Air Traffic Control System Command Center. The figure, which is likely an undercount, is well above the average for weekends before the shutdown.

During weekends from Jan. 1 to Sept. 30, the average number of airport towers, regional control centres and facilities monitoring traffic at higher altitudes that announced potential staffing issues was 8.3, according to the AP analysis.

With reports from Moira Wyton, Eric Atkins and The Canadian Press