If you're headed to an airport this week, there could be snarl-ups and delays. That's because President Donald Trump just joined the leaders of the European Union, Canada, China, and most other countries in grounding all Boeing 737 Max airplanes in the wake of Sunday's deadly crash in Ethiopia that killed all 157 people on the plane, and a similar accident that killed 189 in Indonesia last October.

The news was announced Wednesday morning, at a time when many of the planes were already in the air, carrying passengers. Those planes were to be grounded as soon as they landed, Trump said. 

If you're a frequent traveler or have a flight booked soon, you may be wondering how the grounding will affect you. Here's what we know so far:

1. How likely is my flight to be cancelled or delayed?

It's not a certainty, but it could happen. Before the Ethiopian Airlines accident, Boeing reported that the 737 Max line of planes was its fastest selling ever. Local news is already reporting the cancellation of flights between Nashville and Dallas, and that's sure not to be the only affected route. In all, at least 360 Boeing 737 Max aircraft have been grounded worldwide, and 72 of those are operated by U.S. carriers, with another 24 operated by Air Canada. 

The airline with the most 737 Max planes is Southwest, which flies an all-737 fleet. (Not all 737s are affected by the grounding, only the newer, longer Max models.) Southwest has 34 737 Max aircraft, and it also makes very heavy use of all its planes, turning them around quickly for an average of about five flights a day per plane. 

Do the math, and you can see that Southwest will need to either cancel or find new planes for about 170 flights per day. Since the airline flies some 4,000 flights a day in peak season, it can probably manage that without complete disruption. But it's worth noting that most Southwest flights go out pretty much full, so finding spaces for all the affected passengers could be tricky. And chances are, you're flying Southwest sometime soon: The company says it carries more passengers domestically than any other airline. 

Southwest is not the only heavy user of 737 Max planes. American was flying 24 of them until they were grounded, and United was flying 14 of them. Air Canada was also flying 24 737 Max planes. Given that airlines typically use planes for between two and six flights per day, you can see that among these three airlines, you might expect at least 200 or so daily flights to be affected. But the effect won't be the same everywhere. While Southwest uses 737 Max aircraft throughout its routes, American's Max 8 planes were mostly serving Miami, and United's were mostly serving Houston and Los Angeles, so the chances for delays are greater for flights to and from those airports than elsewhere. And, once again, the 737 Max flights only account for a small percentage of these carriers' service, making it likely they'll be able to replace the aircraft on an affected flight or rebook passengers onto a replacement flight fairly quickly.

The bad news is that given the tight turnaround times with planes and at airports, changes and cancellations like these are likely to have something of a "ripple effect." The good news is, if you were nervous about flying on a 737 Max and wanted to change to a different plane, now you won't have to pay extra to do so.

Incidentally, China Southern Air and Norwegian Airlines have each have more than a dozen 737 Max planes. So if you're flying either of those airlines, your flight could be affected as well. On the other hand, Delta, Virgin Airways, JetBlue, and Alaska Airlines all say they have no Boeing 737 Max planes in their fleets. So if you're flying on one of those carriers, chances are you won't be affected.

2. How long will these planes be grounded?

Nobody knows for sure. The last time a plane model was grounded was January 2013, when the FAA grounded the Boeing 787 Dreamliner due to issues with its lithium-ion battery. It was the first such grounding since 1979. Boeing made modifications to its battery and added several safety features, and the Federal Aviation Administration gave the Dreamliner approval to start flying again in April 2013, just over three months later.

In this case, the ban could be shorter. That's because the same automated safety system suspected of bringing down Ethiopian Airlines Flight 302 on Sunday was also implicated in the Lion Air crash back in October. Under the direction of the FAA, Boeing had already been working on some improvements scheduled to be released sometime next month. 

When that happens, Boeing will doubtless ask the FAA and other governments to lift the ban on the 737 Max aircraft line. Meantime, investigation into the Ethiopian Airlines crash, and even the Lion Air crash, is still ongoing and will likely take a long time to be officially completed.

3. Was it really necessary to ground hundreds of planes and disrupt travel around the world?

Reasonable people can disagree about this, but the answer is probably yes. As the New York Times observed in a fascinating feature that recreates the 12 minutes of Lion Air's ill-fated flight, that plane had already displayed some serious problems on its last flight and should not have flown again until they were fixed. So that crash alone might not have been a good reason to ground the whole Max line, but it raised som disturbing questions about one of the plane's features.

The 737 Max planes have an anti-stalling feature--created to make the planes safer--which automatically lowers the nose of the plane if it's pointed too far up because that can cause jet engines to stall. It seems clear that in the Lion Air incident sensors malfunctioned to make it appear that the plane was pointing too far upward when it was in fact level. The automatic anti-stalling system kicked in and dramatically lowered the plane's nose. The pilots aboard had to struggle with the controls to bring it up again and either were unable to deactivate the system, didn't have the presence of mind to do so as they worked frantically to avoid a crash, or perhaps didn't know to do so since it was a new feature on which pilots were not always properly briefed.

The black boxes from the Ethiopian Airlines crash have been recovered but not yet analyzed, so we're still waiting on definitive answers about that crash. However, the pilot reported flight control problems and asked to return to the Addis Ababa airport shortly after takeoff, and he was an experienced pilot with 8,000 hours of flight time. Satellites showed the Ethiopian Airlines flight going through similar "vertical fluctuations" to the Lion Air flight. And two U.S. pilots had logged complaints about the plane in the months since the Lion Air crash, reporting that the 737 Max planes they flew abruptly lowered their noses when they engaged the automatic pilot system. In both cases, they were able to solve the problem by disengaging automatic pilot and righting the planes manually. Taken together, all these reports suggest that the Boeing 737 Max planes may not be as safe right now as we want them to be. 

In fact Boeing, perhaps bowing to the inevitable, is now supporting the grounding of the 737 Max line. "We are supporting this proactive step out of an abundance of caution," CEO Dennis Muilenburg said in a statement. He added: "We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again." That sounds like something we can all agree on.