March 12 (UPI) -- The United States is increasingly standing alone in its decision not to ground Boeing 737 Max 8 airliners Tuesday after the European Union added its name to the list of countries showing caution over the model.
More than 30 countries -- accounting for about half of the world's fleet of Max 8s -- have grounded the airplane after a Sunday crash in Ethiopia that left 157 people dead. It's the second crash involving the Boeing model in less than six months. An Indonesian Lion Air flight in October killed 189. In both cases, the plane crashed shortly after takeoff.
"As a precautionary measure, [the European Union Aviation Safety Agency] has published today an Airworthiness Directive, effective as of 19:00 UTC, suspending all flight operations of all Boeing Model 737-8 MAX and 737-9 MAX aeroplanes in Europe," the EU said in a statement.
The EU also prevent any airlines from outside the 28-member bloc from operating the models within EU boundaries.
The United States, meanwhile, has yet to issue a grounding order. On Monday, the Federal Aviation Administration, which is working with the National Transportation Safety Board to investigate the crash, said the planes are still airworthy.
But some lawmakers, including Sens. Richard Blumenthal, D-Conn., Mitt Romney, R-Utah and Dianne Feinstein, D-Calif., have called for a grounding of the planes. Blumenthal said he told his family to switch planes if they're scheduled to flight on a Max 8.
He sent a letter to Southwest Airlines, American Airlines and United Airlines asking them to voluntarily ground the Max 8 and Max 9 planes.
"This is the only common sense measure until we have answers and can ensure passenger/crew safety," he wrote.
Sen. Elizabeth Warren, D-Mass, said two recent crashes with the Max 8 raise serious safety concerns, including whether they may have been rushed into service without proper pilot training.
"The FAA should follow [other countries'] lead, reverse their decision, and immediately ground this plane in the United States until its safety can be assured," said Warren, who is running for president in 2020. "Today, immediately, the FAA needs to get these planes out of the sky."
"Out of an abundance of caution for the flying public, the FAA should ground the 737 MAX 8 until we investigate the causes of recent crashes and ensure the plane's airworthiness," Romney tweeted.
Southwest and American are the only U.S. airlines that fly the Max 8, while United flies the Max 9. The former two said they are closely watching developments that could affect the planes.
Several other nations have suspended using the 737 Max 8 -- Brazil, Ethiopia, Indonesia, South Africa, Singapore and Australia. Argentine pilots have refused to fly the aircraft. Britain joined them by grounding its Boeing 737 Max 8 aircraft on Tuesday.
The Irish Aviation Authority made the decision Tuesday to suspend all Boeing 737 Max 8 aircraft from Irish airspace.
During the temporary suspension, the IAA will continue to work closely with the EASA, the FAA and Boeing, Irish authorities said.
The British Civil Aviation Authority stopped all Boeing 737 Max 8 aircraft from arriving, departing or flying over British airspace. The order, done as a precaution, applies to flights from all airlines. Two such flights were rerouted because they had already taken off.
Boeing said it will make a software upgrade for the Max 8 at the direction of the FAA.
"We are confident in the safety of the 737 MAX and in the work of the men and women who design and build it," Boeing CEO Dennis Muilenburg told employees in an email.
No further guidance from Boeing was expected and the manufacturer said it has full confidence in the aircraft.
Eight Americans were on the flight that crashed in Ethiopia -- including California brothers Melvin Riffel and Bennet Riffel, who were returning from Australia when the plane crashed outside Addis Ababa.
"These are two guys that when they're in the room, you really know it," Jake Mangas told NBC News. "These guys were just wonderful, and they're going to be missed deeply by this community [and] for those family and friends that knew them the best."
Antoine Lewis from Matteson, Ill., a commander in the U.S. Army, was aboard the flight while on vacation.
"Losing anyone you love hurts but it's a different hurt when you lose a sibling," Matteson's sister Markita posted to Facebook. "Thank you for always being a awesome big brother always encouraging me, believing in me, and teaching me to live with no fears."
Mucaad Hussein Abdullah of Saint Cloud, Minn., was another American on the flight.