Updated Tuesday to reflect how many 737 planes American Airlines has ordered.

American Airlines and Southwest Airlines will continue flying Boeing 737 Max 8 aircraft as airlines and aviation authorities ground planes internationally after the Ethiopian Airlines crash that killed 157 people.

Southwest Airlines has 34 of the aircraft in its fleet and orders for 219 more from Boeing. In a statement, the company said, "We remain confident in the safety and airworthiness of our fleet of more than 750 Boeing aircraft." A spokesperson for the airline added that the company is in contact with Boeing.

American Airlines operates 24 of the aircraft in its fleet. According to its filings with the Securities and Exchange Commission, it has orders for 20 in 2019 (four of which have arrived, since the count at the end of 2018 was 20); 10 in 2020; and 10 in 2021. It has an additional 40 scheduled for delivery in 2024 and beyond.

The two carriers are the largest operators of the aircraft model in the U.S.

The airline has joined Southwest in assuring concerned travelers on Twitter and in public statements that it has full confidence in its planes and in its staff.

We have full confidence in the aircraft and our crew members, who are the best and most experienced in the industry. — American Airlines (@AmericanAir) March 11, 2019

"At this time there are no facts on the cause of the accident other than news reports. ... We have full confidence in the aircraft and our crew members, who are the best and most experienced in the industry," American Airlines said in a statement.

The Association of Professional Flight Attendants, which represents workers at American, told its members they would not be forced to fly the Max 8 if they felt unsafe. The Association of Flight Attendants-CWA called on the FAA to investigate the Max.

The Boeing 737 is the world's best-selling commercial aircraft. The 737 Max is the latest version in the 737 aircraft family, which accounts for almost one-third of the company's operating profit, according to Bloomberg.

The Ethiopian Airlines crash that claimed the lives of everyone on board, including 22 United Nations staffers, was the second crash of a 737 Max 8 in recent months. There are currently 65 of the aircraft in the U.S. with orders for 548 more from major airlines. A Southwest spokesperson told The Dallas Morning News that the company's current orders for Boeing 737 Max 8 aircraft will go forward as planned.

Boeing issued a statement Monday saying that an investigation into what caused the crash of Ethiopian Airlines flight 302 "is in its early stages, but at this point, based on the information available, we do not have any basis to issue new guidance to operators."

China, Indonesia and Ethiopian Airlines have grounded the jets, and the Federal Aviation Administration said it was "closely monitoring developments." The groundings are significant considering that China is the most important market for Boeing's latest planes.

Travelers who don't feel comfortable flying on a 737 Max can check the details of their booking, which will typically show the type of aircraft, or they can visit flightstats.com.

U.S. aviation regulators signaled their confidence in the safety of the 737 Max family of aircraft, saying they would issue a global notice of "continued airworthiness" on Monday.

"The FAA continuously assesses and oversees the safety performance of U.S. commercial aircraft," the Federal Aviation Administration said in an email announcing plans to issue the notice at 5 p.m. Monday from Washington. "If we identify an issue that affects safety, the FAA will take immediate and appropriate action."

The FAA statement signals that the agency has no immediate intention of grounding the plane.

Bloomberg News and Terry Maxon contributed to this report.