From 8,600 Flights to Zero: Grounding the Boeing 737 Max 8

All Boeing 737 Max 8 aircraft are believed to have been pulled from use worldwide after the model crashed twice in just five months, raising questions about its safety. The United States was the latest country to ground the planes, following Canadian aviation authorities earlier on Wednesday.

Concerns about the model first surfaced after a Lion Air flight crashed near Indonesia in October, killing all 189 people aboard. On Sunday, a second plane crashed outside Addis Ababa, Ethiopia, killing 157 people. It is unclear why the second plane crashed or whether the causes of the crashes are related.

The European Union, China, Indonesia and more than a half dozen countries had already barred the planes from their airspace as the investigation into the Ethiopia crash continued. All 47 airlines that have the Max 8 in their fleets are believed to have stopped flying it.

The Federal Aviation Administration and Boeing originally stood by the plane’s safety, and Southwest and American Airlines continued to fly it in the United States after other airlines had grounded their fleets. The F.A.A. said on Wednesday that an analysis of new evidence collected at the site of the Ethiopian Airlines crash affected its decision.

The 737 class is a workhorse for airlines worldwide, and the single-aisle 737 Max has been Boeing’s best-selling plane ever. More than 340 of the Max 8 planes are registered, and many more are on order.

An estimated 8,600 flights use the plane in a typical week of travel, according to an analysis based on data from Flightradar24, a flight tracking service. But the model accounts for a small fraction of planes in the air at any given time, according to Ian Petchenik, a spokesman for Flightradar24.

The most popular routes are in North America and China.

Investigators recovered both the flight data recorder and the cockpit voice recorder for the Ethiopian Airlines crash on Monday. Some circumstances of the crash, such as unusual altitude changes after takeoff, were similar to those in the Lion Air flight, but the cause is not known.

Five months later, the causes of the Lion Air crash are still under investigation. But the tragedy revealed that Boeing and the F.A.A. determined that pilots did not need to be informed of changes to the Max 8’s flight control system, which may have contributed to the crash.