The Federal Aviation Administration has given approval for the Boeing 737 Max 9 to begin flying again, allowing the planes to return to the skies as early as Friday. This decision comes after part of the fuselage blew out of an Alaska Airlines plane, prompting the FAA to order an immediate grounding and inspection of 171 Boeing aircraft operated by U.S. airlines or in U.S. territory.

With the FAA’s green light, there are still many passengers who might have reservations about boarding a 737 Max 9. Here’s what you need to know as the planes start coming back into service.

Which carriers fly the Max 9?

United and Alaska are the two U.S. carriers of the 737 Max 9, accounting for about two-thirds of the 215 models in service worldwide. Other airlines that fly the plane include Panama’s Copa Airlines, Aeromexico, Turkish Airlines, Icelandair, Flydubai, and SCAT Airlines in Kazakhstan.

How soon will they be back in the air?

Alaska Airlines expects the first of its Max 9 aircraft to return to passenger service on Friday, while United is preparing to return to scheduled service beginning on Sunday.

Checking your flight status

For passengers concerned about their flights, aviation consultant Robert Ditchey suggests using booking sites like Kayak, which now allows users to eliminate and exclude the Max 9 from their search results.