Passenger confidence in Boeing Co.’s 737 Max has taken a hit after the jet’s second fatal crash in just five months.

Travelers around the world took to social media to express fears about the plane’s safety—or seek reassurance from carriers that fly it. Hours earlier, an Ethiopian Airlines 737 Max crashed after leaving Addis Ababa, killing all 157 people on board. Some flyers said they were now too fearful to board one of those planes.

One customer at Southwest Airlines, which has more 737 Max jets on order than any other carrier, changed flights to another aircraft after discovering the plane was a 737 Max. Another asked if Air Canada was doing extra checks on its Max fleet.

The disaster followed the plunge of a Lion Air 737 Max into the Java Sea off the coast of Indonesia on Oct. 29. A preliminary report into that crash, which killed 189 passengers and crew, indicated pilots struggled to maintain control following an equipment malfunction.

Connecting the two incidents, social media users expressed concerns to carriers that operate or have ordered the Max, from Ryanair and Garuda to Fiji Airways and Norwegian Air. Already in China, authorities grounded the country’s entire fleet of 737 Max 8 planes, while Cayman Airways, the flag carrier of the Cayman Islands, suspended operations of both its Max 8 aircraft.

Any widespread veto by flyers would put extra pressure on Boeing.

In response, Southwest and Iceland Air were among the airlines to back their choice of aircraft. Boeing has said it’s preparing to send a technical team to assist the accident investigation of the Ethiopian Airlines plane, which was delivered new in November.

Iceland Air said the 737 Max carries out around 1,000 trips a day worldwide. The airline has three of the aircraft and has never had an incident, it said.