Planes grounded again as officials investigate how panel blew out on Alaska Airlines flight

U.S. authorities asked the public on Sunday to help find a panel that blew off a passenger airplane above Oregon, while AlaskaAirlines grounded its 737-9 Maxjets for a second time after federal officials indicated further maintenance might be required to assure it doesn't happen again.

The door plug tore off the left side of a new AlaskaAirlines Boeing 737-9 Max jet at 4.8 kilometres above ground on Friday, about six minutes after takeoff from Portland, Ore.,en route to Ontario, Calif. Videos posted online by passengers showed a gaping hole where the panelled-over exit had been and passengers wearing oxygen masks.

Pilots turned around to land the depressurized plane back at the Portland International Airport. All 171 passengers and six crew members survived the flight, with only a few minor injuries reported.

Alaska Airlines had returned 18 of its 65 737-9 Maxaircraft to service on Saturday following inspections that came less than 24 hours after the incident. The airline said in a statement that the decision to ground them again was made after receiving a notice from the U.S. Federal Aviation Administration (FAA) that additional work might be needed.

"These aircraft have now also been pulled from service until details about possible additional maintenance work are confirmed with the FAA. We are in touch with the FAA to determine what, if any, further work is required before these aircraft are returned to service," the airline said.

WATCH | U.S. regulator grounds 171 Boeing 737 Max planes:

FAA investigates after Boeing 737 cabin panel blows out at 16,000 feet

9 months ago

Duration 2:39

U.S. airline regulators have temporarily grounded 171 Boeing 737 Max 9 planes after a terrifying non-fatal incident aboard an Alaska Airlines flight. A cabin window blew out and depressurized the passenger cabin in mid-air, forcing an emergency landing.

The FAA said 171 of the planes will remain grounded until the agency is convinced they can operate safely.

"We have grounded the affected airplanes, and they will remain grounded until the FAA is satisfied that they are safe," the agency said on Sunday.

National Transportation Safety Board chair Jennifer Homendy told a news conference late Saturday that the missing panellikely landed near Oregon Route 217 and Barnes Road, in the Cedar Hills area west of Portland.

Homendy said it was extremely lucky that the airplane had not yet reached cruising altitude, when passengers and flight attendants might be walking around the cabin.

WATCH | McGill University professor on emergency landing by Alaska Airlines:

CBC News Networks Neil Herland speaks with a professor of Aviation Management Program from McGill University about the emergency landing made by Alaska Airlines.

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Get the latest on CBCNews.ca, the CBC News App, and CBC News Network for breaking news and analysis.

She said the two seats next to the portion of fuselage that blew out were unoccupied. Parts of the seat next to the fuselage, including the head rest, were missing.

"We are very, very fortunate here that this didn't end up in something more tragic," Homendy said.

The National Transportation Safety Board's investigation of the incident is expected to take months.

The fuselage for Boeing 737s is made by Kansas-based Spirit AeroSystems, which separated from Boeing in 2005. Spirit manufactured and installed the plug that suffered the blowout, asource told Reuters on Saturday.

John Cox, a former pilot and CEO of the U.S. aviation consulting group Safety Operating Systems, based in Washington, D.C., said on Sunday that this particular type of door plug has been in service for 15 years and is a "proven design."

Investigators will need to check the paperwork on the plane's assembly to determine who the last person was to touch the plug and whether there was a safety inspection done after it was assembled, he told CBC News, as well as what process was used to assemble and inspect it.

Cox said the plug is held into position by four bolts. "And now the question is, were those four bolts installed? If they were, were they properly torqued? And was the proper hardware utilized to lock those bolts in place and to distribute the load appropriately, meaning that were necessary washers and things like that there?" Cox said.

"If one of those or more were not in place or not properly installed, after a number of flights, they're going to vibrate. And if one or two of them came out, now the door can rise up.... And at that point, then it could depart the airplane."

Sources familiar with the installation process said Boeing also has a potentially key role, since it typically removes the semi-fitted left-side door panel to feed in cabin equipment andspeed up production before completing final installation.

WATCH | Investigation underway into mid-air blowout of jet panel:

Investigation underway into midair blowout of Boeing jet panel

9 months ago

Duration 4:31

An Alaska Airlines flight was forced to make an emergency landing on Friday after a window and piece of fuselage blew out in midair. John Cox, a former pilot and the president of Safety Operating Systems, discusses what investigators will be looking at and what passengers should do if they find themselves in a similar situation.

Investigators are expected to examine whether any installation flaws occurred at Spirit or Boeing plants, sources said.

The vast majority of that model of plane used in the U.S. are operated by United Airlines and Alaska Airlines, while Turkish Airlines, Panama's Copa Airlines and Aeromexico also grounded jets for inspections.

Canadian airlines say they don't fly the Max 9 jetliners.Airlines including Air Canada, WestJet, Flair Airlines and Lynx Air all say they fly the 737-8 Max jetliner.