On Thursday, PHL experienced numerous delays and cancellations, with officials warning that the number is expected to grow.
"It's Thursday, just kind of want to get home to my family, so it's annoying," said Kate Kelly of Natick, Massachusetts. "There's nothing else. No other flights. The Delta reps told me I'm better off taking Amtrak."
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Transportation leaders are calling this a proactive measure to relieve the pressure on staffing, with TSA agents and air traffic controllers going without a second paycheck on Friday.
"Our sole role is to make sure that we keep this airspace as safe as possible [by reducing] capacity at 40 of our locations. This is not based on light airline travel locations. This is about where the pressure is and how to really alleviate the pressure," said FAA Administrator Bryan Bedford.
The FAA says thousands of flights could be impacted daily.
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AAA urges travelers to stay up-to-date on their flights and always have a plan B.
"That plan B can mean that you are now renting a car, you're changing the mode of transportation that you're using to get to your destination," officials said.
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Transportation Secretary Sean Duffy said earlier this week that the FAA will be forced to shut down the airspace in some areas if the shutdown continues into next week.
"Instead of flying into Boston, we're gonna try to fly in Providence. Hopefully, we'll be able to get home," said Julia Guidone.
The reduction in capacity marks an unprecedented move by the FAA and the Department of Transportation. Bedford said he has never seen this happen before in his 35-year career.
Both Bedford and Duffy emphasized that the decision to cut down flights is a proactive measure based on data the department has reviewed, and the staffing pressures anticipated to grow during the shutdown. Duffy said the action is being taken to "reduce the risk profile in the national airspace."
Echoing him. Bedford added, "We're not going to wait for a safety problem to truly manifest itself when the early indicators are telling us we can take action today to prevent, you know, things from deteriorating. So the system is extremely safe today, and it will be extremely safe tomorrow."
Travelers say they understand these last-minute adjustments.
"If it's a safety thing, that's the most important thing," said Haili Declouet, Lafayette, La.
Bedford said the cuts to each airline's flight schedules will be proportionate, adding that the agency recognizes there's "no perfect solution."
The FAA said it will consider various factors when finalizing the cuts, including airlines that already operate a less-than-daily service at an airport.
Airlines for America, a trade association representing many major U.S. airlines, released a statement after the announcement, saying, "We are working with the federal government to understand all details of the new reduction mandate and will strive to mitigate impacts to passengers and shippers."
Here's a list of U.S. airports to be impacted exclusively obtained by ABC News
- ANC Anchorage International
- ATL Hartsfield-Jackson Atlanta International
- BOS Boston Logan International
- BWI Baltimore/Washington International
- CLT Charlotte Douglas International
- CVG Cincinnati/Northern Kentucky International
- DAL Dallas Love
- DCA Ronald Reagan Washington National
- DEN Denver International
- DFW Dallas/Fort Worth International
- DTW Detroit Metropolitan Wayne County
- EWR Newark Liberty International
- FLL Fort Lauderdale/Hollywood International
- HNL Honolulu International
- HOU Houston Hobby
- IAD Washington Dulles International
- IAH George Bush Houston Intercontinental
- IND Indianapolis International
- JFK New York John F Kennedy International
- LAS Las Vegas McCarran International
- LAX Los Angeles International
- LGA New York LaGuardia
- MCO Orlando International
- MDW Chicago Midway
- MEM Memphis International
- MIA Miami International
- MSP Minneapolis/St Paul International
- OAK Oakland International
- ONT Ontario International
- ORD Chicago OHare International
- PDX Portland International
- PHL Philadelphia International
- PHX Phoenix Sky Harbor International
- SAN San Diego International
- SDF Louisville International
- SEA Seattle/Tacoma International
- SFO San Francisco International
- SLC Salt Lake City International
- TEB Teterboro
- TPA Tampa International
ABC News contributed to this report.