The U.S. Federal Aviation Administration issued a directive on Saturday temporarily grounding certain Boeing 737 MAX 9 airplanes until inspections are performed after an Alaska Airlines flight on Friday made an emergency landing following a cabin panel blowout.

The directive covers 171 airplanes, but leaves open questions about how recently inspections must have occurred before further flights can take place or detail the precise inspection requirements.

The FAA said the potential in-flight loss of a mid-cabin door plug "could result in injury to passengers and crew, the door impacting the airplane, and/or loss of control of the airplane."