Travelers asking airlines: Is the Boeing 737 MAX 8 safe to fly?

Three U.S. airlines fly more than 70 of the planes.

Is there any connection between the two crashes?

ABC News’ Senior Transportation Correspondent David Kerley reports:

Though both involved the same plane, it’s too early to make a connection between the deadly plane crash that killed 157 people near the capital of Ethiopia on Sunday and the crash that killed 189 people in Indonesia in October.

Though there is a lot of information from the Lion Air crash, which experts say was likely caused by a combination of maintenance and pilot error issues, there’s still very little information available from the crash in Ethiopia.

It’s promising that responders found two black boxes at the site of the Ethiopia crash — but how quickly experts can recover data from the crash will depend on the conditions the black boxes are in. The investigation could take weeks or months.

What’s significant from the little information that is known, however, is that shortly after takeoff, both airplanes had flight control issues. The data available so far from the crash in Ethiopia is that the aircraft started “porpoising,” or tilting up and down because of a problem with vertical airspeed.

The plane crashed within six minutes of takeoff.

The Boeing 737 is the best-selling jetliner ever — considered the workhorse of aviation -- and the MAX 8 is the latest derivative, with upgrades and new technology.

The question now comes down to whether there is something inherently wrong with this brand new aircraft.

Though both pilots in both incidents were dealing with flight control issues, the two crashes could also turn out to be completely different.

Watch the full report from ABC News’ Senior Transportation Correspondent David Kerley here.

Which airlines fly the Boeing 737 MAX 8 and where?

ABC News’ transportation reporter and producer Jeffrey Cook reports:

ABC News spoke to the three airlines that fly the MAX 8 in the U.S. and all three confirmed they would continue to do so, expressing confidence in the airplane. There are 72 flying in the U.S. currently and 350 worldwide — with a backorder of around 4,600.

Here’s the breakdown by airline:

American Airlines has 24 in its fleet, mostly based out of Miami and serving its Caribbean routes.

Southwest Airlines has 34 in its fleet, operating routes all over the country, including the Boston-Houston route, the Vegas-Chicago route and the Austin, Texas-Reagan National Airport in Washington, D.C., route.

United Airlines doesn’t operate any MAX 8 airplanes but operates 14 MAX 9s — a longer model of the MAX 8 that can hold more passengers. Those planes mostly fly out of Houston.

How can passengers find out if they’re scheduled to fly on a Boeing 737 MAX 8?

ABC News’ transportation reporter and producer Christine Theodorou reports:

Many ticket holders have taken to Twitter, trying to figure out if their upcoming flights are on a Boeing 737 MAX 8. Generally, they’re finding out that there’s no guarantee which plane they’ll be flying until around 24 hours before their flight leaves.

“You would have to reach out to us roughly 24 [hours] prior to your flight so that we can see which aircraft we will be utilizing to fly that route,” a customer service representative for Southwest Airlines responded to a concerned customer on Twitter Monday morning.

In another tweet, the same representative dismissed another concerned passengers questions about aircraft type and possible reservation changes because of it, insisting Southwest remained confident in the safety of all of its Boeing airplanes, including the latest 737 MAX 8 version.

“Southwest has operated approximately 31,000 flights utilizing the Boeing 737 MAX 8 aircraft, and we plan on operating those aircraft going forward,” the tweet stated.

"We remain confident in the safety and airworthiness of our entire fleet of more than 750 Boeing 737 aircraft, and we don’t have any changes planned to 737 MAX operations," Southwest said in a statement.

"We are fielding some questions from Customers asking if their flight will be operated by the Boeing 737 MAX 8. We are not, however, observing a high number of cancellations or reschedules," the statement said. "Our Customer Relations Team is responding to concerned Customers individually, emphasizing our friendly, no-change-fee policy.”

American Airlines similarly tweeted from its account, saying “We have full confidence in the aircraft and our crew members, who are the best and most experienced in the industry.”

American wouldn’t say whether it's received cancellation requests or if it's making accommodations for frightened passengers.

Neither Southwest nor American is bending their rules for flight change fees, despite the new fears, they both said in response to customers on Twitter Monday.

United, which flies a Boeing 737 that’s similar but larger than the MAX 8 called the MAX 9, said on Twitter that if a passenger preferred not to fly that plane they would “do what is best in our capabilities to find alternative travel arrangements.” They did not say if that meant waiving change fees.

United responded to most passengers that it has confidence in its pilots, who are “properly trained to fly the 737 MAX 9 aircraft safely.”

ABC News' Morgan Winsor contributed to this report.