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As countries around the world are grounding all Boeing 737 Max planes after the Ethiopian Airlines crash on Sunday that killed 157 people, U.S. passengers are growing concerned after the FAA announced airlines can still fly the Boeing jet in the country.

Passengers are taking to social media, expressing their anxieties about flying on one of the Boeing models and asking their airlines how to know if they’ll be on a 737 Max 8 or 737 Max 9.

So @southwestair, are you grounding your 737 Max 8s? I’m supposed to fly in one with you next week between OAK and SEA. Let me know - otherwise, I’m changing my flight. — Marla Wilson (@dcmarla) March 11, 2019

Currently, Southwest Airlines has 34 Max 8s, and American has 24. United doesn’t fly the Max 8, but it does fly 14 Max 9s.

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If a passenger is worried, looking up the model of the plane isn’t too difficult.

When buying tickets, airlines often list the model of plane with the ticket information.

On Southwest, click the specific number of the flight and it will list the plane model. When looking for tickets on United, click the “details” button. On American, it will be listed with the flight information, near the time and price (American denotes the 737 Max 8 with the shorthand 7M8 on their website).

Additionally, Kayak, the online airfare aggregator and travel search engine, announced this week they will soon introduce filters that allow users to search for tickets by plane model. The decision came from user feedback who were requesting the feature, a Kayak representative told NBC News.

If you’ve already bought your ticket, the plane information should be on your ticket. If you can’t find it, call the airline and it’ll let you know.

Southwest passengers can always change their tickets free of charge, and United said if you prefer not to fly the 737 Max 9 the airline “will do what is best in our capabilities to find alternative travel arrangements.”

Still, airlines can change planes at the last minute.

While the FAA said it's confident that U.S. airlines can still safely fly the 737 Max fleet, for some passengers, it's not enough to assuage their anxieties.

Marie Clark-Burch wrote to Southwest on Facebook saying she was disappointing they haven't grounded the planes.

"I actually was in one on Monday and was a nervous wreck," she said.