Boeing has been asked to revise the inspection and maintenance instructions it had recommended for operators of grounded Boeing 737 Max 9 aircraft, the FAA said Tuesday afternoon, leaving an uncertain timeline for when airlines will be able to begin returning those planes to service.
The announcement likely portends to behind-the-scenes acrimony over the inspection specifications between Boeing, impacted airlines and regulators.
On Monday, the FAA said that it had approved an inspection methodology for the aircraft, which it grounded after an exit door plug blew out of an Alaska Airlines flight shortly after departing from Portland, depressurizing the cabin and forcing an emergency landing.
But in statements later on Monday, Alaska and United, which combined operate 144 of the 171 grounded Max 9 planes, said that they were continuing to wait for final documentation from Boeing and the FAA.
The FAA now says that initial version of instructions is being revised due to the feedback it generated.
"Upon receiving the revised version of instructions from Boeing the FAA will conduct a thorough review," the agency said. "The safety of the flying public, not speed, will determine the timeline for returning the Boeing 737-9 Max to service."
Missing bolts on the door plug that blew out of the Alaska Airlines plane are now at the center of the National Transportation Safety Board's investigation into the incident. United has also reported that preliminary inspections of grounded Max 9 aircraft had turned up what appear to be loose bolts on some emergency exit door plugs. And Alaska said that its technicians have noted visible "loose hardware" on some of its Max 9 planes.
The plugs are used by some Max 9 operators in place of an exit door that would be required if the plane were configured with a larger number of seats.
Alaska flight 1282 had ascended to 16,000 feet several minutes after departure from Portland on the evening of Jan. 5 when the door plug disengaged. The plane was able to return to Portland and land without casualties.