By David Shepardson
WASHINGTON (Reuters) -The Federal Aviation Administration issued a directive on Saturday temporarily grounding certain Boeing (NYSE:BA) 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."
Friday's structural failure of the Alaska Airline-operated plane left a rectangular hole in an area of fuselage reserved for an optional extra door, but which is disactivated on Alaska's aircraft and fitted with a special door replacement "plug."
The FAA's emergency airworthiness directive requires operators to inspect aircraft before further flight that do not meet the required inspection cycles, but it does not detail the precise figure.
The FAA must approve any inspection requirements that Boeing proposes.
Required inspections will take around four to eight hours per aircraft, the FAA said.
Alaska Airlines said that after it had voluntarily temporarily grounded its fleet of 65 737 MAX 9 aircraft early Saturday, "it was determined that 18 had in-depth and thorough plug door inspections performed as part of a recent heavy maintenance visit. These 18 aircraft were cleared to return to service today."
United Airlines, the only other U.S. airline that operates Boeing's 737 MAX 9 jets, said it temporarily suspended service of 45 737 MAX 9 aircraft but would continue to operate 33 that have already received the necessary inspection that is required by the FAA.
Alaska canceled about 140 flights on Saturday, or 18% of scheduled operations, according to FlightAware, while United said it expected to cancel 60 flights because of the service issue.
The president of the Association of Flight Attendants-CWA, Sara Nelson, said the union "supports the FAA's quick and decisive action to ground certain 737 MAX 9 Fleet that do not meet the inspection cycles specified in the Emergency Airworthiness Directive."
Lawmakers called for quick action if any issues are discovered. "The NTSB (National Transporation Safety Board) and FAA must thoroughly investigate this incident to address an alarming breach of safety," said Senator Ted Cruz, the top Republican on the committee overseeing the FAA.