As the investigation continues into the fatal crash of a 737 Max 8 in Ethiopia on Sunday, regulators in China and Indonesia are grounding the planes, and some airlines in other countries are voluntarily pulling their fleets from service.

In the United States, the Federal Aviation Administration, which certified the latest version of Boeing’s best-selling jet as airworthy in 2017, has not taken that step despite mounting questions about the plane’s safety record. The agency released a memo, known as a Continued Airworthiness Notification to the International Community, on Monday night that made no mention of plans to ground 737 Max planes.

Robert W. Mann, an airline industry consultant in Port Washington, N.Y., described what a grounding entails and the factors regulators consider when making the decision to order one. His responses have been condensed and edited for clarity.

What is a grounding?

A grounding occurs when the relevant safety regulator (the F.A.A. in the United States, or the European Aviation Safety Agency in Europe) removes the airworthiness certificate for a certain kind of plane. Effectively that makes those airplanes unusable in that jurisdiction, and also in other jurisdictions that have accepted a particular regulator’s authority.

Groundings come in a variety of forms. They can require planes be taken out of service immediately, even before a remedy has been specified, or they can come with a remedy specified. Airplanes can also be grounded after a certain number of hours or flights, during which the airlines that operate the affected aircraft can decide when and how to inspect and repair them. That kind of grounding happened most recently after the engine failure on Southwest Airlines Flight 1380 last spring prompted the F.A.A. to order closer inspections of a type of engine made by CFM International.