What travelers need to know

Airlines have canceled hundreds of flights since the Federal Aviation Administration ordered carriers to take Boeing 737 Max 9 planes out of service for urgent inspections.

Here’s what travelers should know:

The FAA grounded more than 170 Boeing 737 Max 9 planes so they can be inspected after a door plug panel blew out on Alaska Airlines Flight 1282 on Friday. No one was seriously injured on the Ontario, California-bound flight, which returned to Portland, Oregon, when the incident occurred minutes into the flight at about 16,000 feet.

United Airlines and Alaska Airlines are the biggest operators of the Boeing 737 Max 9, with 79 and 65 of the planes in their fleets, respectively.

United canceled 229 mainline flights on Monday, representing about 8% of its schedule, according to FlightAware. The carrier has been using other types of aircraft, where possible, to avoid cancellations.

Alaska Airlines, which has fewer types of planes in its fleet compared with United, canceled 143 flights, about a fifth of the day’s schedule.

United scrubbed 385 flights over the weekend, while Alaska canceled 328 flights.

Other carriers including Panama’s Copa and Aeromexico are affected by the inspection order. Copa has canceled more than 150 flights since Saturday, and Aeromexico has canceled 100 during that time, FlightAware shows.

The more common Boeing 737 Max 8 plane is not affected.

United and Alaska have put travel waivers in place that allow customers to rebook their flights without paying change fees, or to cancel their…