On Sunday, an Ethiopian Airlines plane crashed after taking off from Addis Ababa, . The plane was a 737 MAX 8, the same model that also crashed shortly after takeoff in Indonesia in October. Boeing debuted the 737 MAX 8 less than two years ago, making it brand-new by plane standards.

Aside from the fact that commercial airline crashes , the fact that two versions of the same new plane model crashed for unknown reasons within months has caused global alarm.

So what the hell is going on here? The short answer: right now nobody knows, exactly.

What is the 737 MAX 8?

The Boeing 737 MAX series is designed to compete with the Airbus A320neo series. With greater fuel efficiency and range, these planes are more operationally flexible and economical for airlines to operate versus their predecessors, like the 737-800 and A320.

The 737 MAX 8s can fit up to 210 passengers (without a first-class configuration), 21 more than the 737-800, and has a maximum range of 3,550 miles. According to the New York Times, 737 MAX 8s.

How have airlines and regulators reacted to the crash?

Some are using the uncertainty to ground all MAXs (including the MAX 9s, used by United Airlines, as well) for an undetermined amount of time. Others are using the uncertainty about the crash cause to argue that grounding the fleets is premature given that we don’t know what’s going on and most MAX 8s have been operating safely.

Still, most Max 8s at this point are effectively grounded. At least 34 airlines their MAXs as of this writing including China Southwestern Airlines and Norwegian Air. In total, the New York Times says about two-thirds of the fleet is out of service.

But Southwest, American, and Air Canada, which have the three largest MAX 8 fleets in the world with 82 planes between them, have not grounded theirs yet. The Federal Aviation Administration maintains that the planes are still safe to fly, but airline regulators in Europe, China, and Australia, among other places, apparently do not agree.

At this point, it’s not clear why the U.S. and Canadian authorities differ from the other major regulators. But the New York Times reports Boeing’s CEO did call President Trump to urge the fleet to stay in the air and argued the planes are safe. The company also says they will be issuing a software update.

Yes. Although investigations for both crashes are still underway, Ethiopian Airlines CEO Tewolde GebreMariam they were having “flight control problems” shortly before the crash.

This only furthered suspicion that there is something wrong with the plane’s angle of attack sensors or the software that governs them, as in the Lion Air crash.

And pilots have been warning the FAA for months that the training manuals for the MAX 8s are woefully inadequate and could result in exactly the types of crashes the Lion Air and Ethiopian Airways planes experienced.

Why didn’t the Lion Air crash force MAX 8s to be grounded?

One potential reason is that Lion Air . The Guardian reported investigators before the fateful flight.

But aviation experts quickly noted after the crash that Ethiopian Airlines , which made the second crash all that more alarming.

How do I find out if I’m flying on a MAX 8 or 9?

You can type in your flight information at your airline website or a third-party tracker like But even if you are flying on a MAX 8, it’s worth remembering some 350 of these planes were operating worldwide before the groundings, conducting thousands of flights a week. The odds are still pretty darn good for a safe journey—hopefully.

: Canada and the United States , which means the entire fleet is effectively out of service.