When you fly, do you pay attention to what type of aircraft you're on out of safety concerns? A lot of people who never thought about this question are considering it this week, after China and Indonesia both grounded all Boeing 737 Max 8 planes in their nation's fleets out of safety concerns. Several international airlines have followed suit.

But U.S. carriers that use the model are continuing to fly them. That includes Southwest Airlines, which has 34 Boeing 737 Max 8 planes in its fleet, and American Airlines, which has 24 of them, according to the New York Times. Air Canada has 24 of them as well, and says it will continue to fly them. So will Canadian carrier WestJet, which has 13 of the planes.

Concerns about the Boeing 737 Max 8 surfaced on Sunday, when Ethiopian Airlines Flight 392, a 737 Max 8 plane, crashed shortly after takeoff from Addis Ababa, Ethiopia, bound for Nairobi, Kenya, killing all 157 people aboard. Flight data shows the plane gaining and losing altitude rapidly before it slammed into the ground, although eyewitnesses say it was veering and swerving, and that black smoke was pouring out of it. 

That accident may be similar to another 737 Max 8 crash in October, that of Indonesian carrier Lion Air Flight 610, which plunged into the ocean shortly after takeoff killing all 189 people aboard and making 2018 the worst year for airline fatalities in five years. Black box data shows the pilots on that flight struggling with a software system that erroneously thought the plane's nose was pointed too far up and kept forcing it lower. On its previous flight, that plane, which may have been poorly maintained, gave incorrect altitude and speed readings, and so it never should have been used for that flight. Lion Air is reportedly suspending planned delivery of four more 737 Max planes as a result of the Ethiopia crash.

Unlike Lion Air, Ethiopian Airlines has a very good safety record. The second crash was enough to persuade China and Indonesia to ground all 737 Max 8 planes in their country's carriers, and for Singapore to ban the model from its airspace. Here in the United States, the Association of Flight Attendants has sent a letter to the Federal Aviation Agency calling for a review of the model and expressing concern about its safety record, while two U.S. senators, Dianne Feinstein (D) of California and Richard Blumenthal (D) of Connecticut, have called for grounding the 737 Max 8 until the investigation into the Ethiopian Airlines crash is complete--which could take years. The investigation into the Lion Air crash is still ongoing.

As for the FAA, it's released a  continued airworthiness notification about the Max 8 to the international community. Noting that some observers claimed there wotere similarities between the Lion Air and Ethiopian Airlines accidents, the notification says, "However, this investigation has just begun and to date we have not been provided data to draw any conclusions or take any actions."

The FAA goes on to note that Boeing is making improvements to the software system that may have been involved in the Lion Air crash, and that the FAA expects to make these improvements mandatory for airline in April. And Boeing has issued a statement saying that these improvements are "designed to make an already safe aircraft even safer." Among other things, the enhancements will limit how much the automatic system can lower the plane's nose if it erroneously detects that the plane is pointing too far upward. Meanwhile, both Southwest and American have issued statements saying they have complete confidence in the safety of the aircraft.

If that's not enough to convince you, United and Delta both say they don't have any Boeing 737 Max 8 planes in their fleets. That may be something to consider next time you book a flight.