More travelers are reaching out to U.S. airlines, especially Southwest Airlines and American Airlines, asking to change flights scheduled on 737 Max 8 jets, the type of aircraft that crashed in Ethiopia on Sunday and has since been grounded by a growing number of countries.

But so far, just a handful of Boeing’s new planes are arriving or departing from Philadelphia International Airport. The 737 Max 8 had one arrival and three departures, all on Southwest Airlines and scheduled on Tuesday and Wednesday, according to FlightRadar24.com on Tuesday afternoon.

These include Southwest flight #1029 arriving from Tampa at 5:40 p.m. Wednesday and a scheduled departure Thursday at 7:05 a.m., to Atlanta on flight #2348.

By Wednesday, Southwest was switching some of the flights to older aircraft in the 737 series.

The Federal Aviation Administration says the plane is safe, and so do the U.S. airlines using it. Southwest is running the largest fleet of 737 Max 8 jets, with 34 in service throughout its system, while American has 24 in its fleet. United Airlines flies a slightly larger version, the Max 9. More than 30 airlines operate a total of about 350 737 Max 8s.

A Week of 737 Max 8 Flights in Philadelphia

From Feb. 28 to March 3, 19 flights using Boeing 737 Max 8 aircraft departed or arrived at Philadelphia International Airport. All but two of the flights were operated by Southwest Airlines.

Airline:

Southwest

American

Chicago

(Midway)

Philadelphia

4

5

Denver

4

Nashville

(Miami)

2

Atlanta

Dallas

(Love Field)

Orlando

Ft. Lauderdale

Miami

Airline:

Southwest

American

Chicago

(Midway)

Phila.

4

5

Denver

Nashville

4

2

Miami

Atlanta

Dallas

(Love Field)

Orlando

Fort Lauderdale

SOURCE: Flightradar24
JOHN DUCHNESKIE / Staff Artist

Several customers have asked on social media whether their Southwest or American Airlines flights were on the 737 Max 8 and looked to change them. But carriers do not offer fee waivers for switching flights and accommodations to travelers who want to avoid the Max 8.

Southwest announced on Twitter that it’s not offering any special deals to people who want to change their reservations to avoid the plane. “If you would like to change your flight, there would be a difference in fare that would need to be collected for doing so,” a Southwest representative said on the social-media platform.

American Airlines said in a statement that it will continue to collaborate with the FAA. "We have full confidence in the aircraft and our crew members, who are the best and most experienced in the industry.”

Aviation experts say customers should avoid booking flights with 737 Max 8 to avoid potential cancellations. If the Ethiopian crash was caused by the model’s new piloting software, as some observers suspect, the plane could be grounded worldwide until it is tested and revamped, if needed.

Paul Hudson, FlyersRights.org president and a member of the FAA Aviation Advisory Committee, said customers flying on the 737 Max should reschedule their flights if they feel more comfortable doing so.

“The FAA’s ‘wait and see’ attitude risks lives as well as the safety reputation of the U.S. aviation industry,” Hudson said. “Even assuming this design defect should not by itself take the aircraft out of service, the failure to warn airlines and pilots of the new feature, and the inadequacy of training requirements, necessitate an immediate temporary grounding of the Boeing 737 Max 8."

Hudson said that serious questions over Boeing’s MCAS safety system need answers and the aircraft should be re-certified. Concerns include inaccurate or nonexistent information in Boeing’s training manuals and inadequate flight training requirements.

Airline pilots on at least two U.S. flights have reported that an automated system seemed to cause their Boeing 737 Max planes to tilt down suddenly, the Associated Press reported.

The pilots said that soon after engaging the autopilot on Boeing 737 Max 8 planes, the nose tilted down sharply. In both cases, they recovered quickly after disconnecting the autopilot. As described by the pilots, however, the problem did not appear related to a new automated anti-stall system that is suspected of contributing to the deadly October crash in Indonesia.

With European aviation regulators grounding all Boeing 737 Max 8 flights, about two-thirds of the global fleet is off-line after that type of aircraft’s fatal crash in Ethiopia killed 157 people. Sunday’s crash marked the second time in less than five months that the new Boeing plane crashed and killed everyone on board. The previous crash occurred on a Lion Air flight over the Java sea.

Boeing planes have been banned in Britain, Australia, China, Indonesia, Morocco, and elsewhere in the last two days over safety concerns following the crash in Ethiopia.

The 737 Max has bigger engines than the original 737, which make it 14 percent more fuel-efficient than the previous generation. Experts say that issues with the 737 Max’s new piloting software, the Maneuvering Characteristics Augmentation System (M.C.A.S.), and angle-of-attack sensors may have played a role in the two accidents, which both occurred after takeoff.

Boeing said Tuesday that the FAA wasn’t requiring any further action and the company doesn’t have “any basis to issue new guidance to operators.” The company said on Monday that it was in talks with regulators and airlines to discuss their concerns. “We are confident in the safety of the 737 MAX,” CEO Dennis Muilenburg said in a message to employees. Boeing said it wouldn’t discuss any talks it was having with customers.

The FAA said it stood by the 737 Max’s safety performance and “has not been provided data to draw any conclusions or take any actions,” such as grounding the model. The agency said it expected to mandate release of a software disk believed to have played a central role in the first plane crash, in Indonesia.