The Deadly Southwest Engine Explosion Is a Dangerous Warning Sign for Thousands of Planes

The deadly engine explosion on Southwest Airlines Flight 1380 could be more than just an isolated incident.

The engine is one of the most common in the world, used on more than 8,000 Boeing 737 aircraft. Couple that with the fact that the same problem led to a similar catastrophic engine failure two years ago, and investigators are scrambling to figure out whether Tuesday’s incident is evidence of a wider design flaw that could force regulators to disrupt air travel by grounding a huge portion of the fleet for U.S. airlines.

“I’m very concerned about this particular event,” National Transportation Safety Board Chairman Robert Sumwalt said at a news conference on Wednesday. “If we feel there is a deeper issue, we have the capability to issue urgent safety recommendations.”

The engine – a CFM56-7B manufactured by CFM International, a partnership of GE and French firm Safran SE – is the most common engine on the most common commercial aircraft in the world, the 737, which is made by Boeing.

Robert Anderson, a professor of aerospace engineering at Embry-Riddle Aeronautical University, tells TIME that the CFM56-7B engines have been used on countless commercial flights across the world without incident. He is doubtful that what happened on Tuesday is evidence of a design flaw.

“Is this an engineering problem? The answer is likely no, because you’d see it happening in other places,” he says

A passenger was partially sucked out a window that shattered when an engine on Southwest Flight 1380 exploded Tuesday. Investigators believe one of the jet engine’s blades broke and came loose, which caused the engine to fail. The flight, which left from New York and was scheduled to land in Dallas, made an emergency landing in Philadelphia. Jennifer Riordan, a bank executive and mother of two, who had been partially sucked out the window, later died. It was the first U.S. airline death since 2009.

Anderson says that type of catastrophic failure is “very rare.” Modern jet engines are designed to contain a blade that breaks off.

“A single blade failing should be contained within the engine without having pieces go radially outward,” Anderson says.

This appears to be at least the second time a broken fan blade has caused a major engine failure. In 2016, a Southwest flight with the same CFM56-7B engine safely landed in Florida after a fan blade broke off. It was later determined that metal fatigue – cracks that form as metal weakens through use and stress over time – was to blame. The FAA proposed mandatory inspections of fan blades on several Boeing 737s, but never followed through and issued a final decision on the matter.

In the wake of Tuesday’s incident, the FAA is now taking action. The agency announced it will issue an order in the next two weeks requiring ultrasonic inspections of some CFM56-7B engines to check for metal fatigue in fan blades.

Officials inspecting the engine failure further will look for one of three factors to explain why metal fatigue led to the splintering of the fan blade, according to Anderson. They include investigating whether engineering problems caused the engine to blow out, whether the batch of metal used to build the engine was faulty or if a one-off event led to the engine’s eventual failure.

“If you have a design problem, they’ll ground all those engines,” he says.

If Boeing 737s are grounded, it could be especially bad for Southwest Airlines, whose fleet is made up entirely of the model.