Explainer: Now-found door 'plug' may hold vital clues to how a gaping hole blew open on a jetliner
Few people thought much about “plugs” that seal unused exits on planes until one of them failed and blew a hole in an Alaska Airlines jet
Investigators said Sunday they had found the piece of fuselage that blew off a Boeing airliner over Oregon on Friday, and hoped it would provide physical evidence of what went wrong.
The gaping hole in the side of the Alaska Airlines jet opened up where aircraft maker Boeing fits a “plug” to cover an emergency exit that the airline does not use.
The plugs are on most Boeing 737 Max 9 jets. The Federal Aviation Administration has temporarily grounded those planes until they undergo inspections of the area around the door plug.
Some larger Boeing 737s have emergency exits on fuselages behind the wings to meet a federal requirement that planes be designed so passengers can evacuate within 90 seconds even if half the exits are blocked.
The more passenger seats there are on a plane, the more exits are required.
Some carriers, including Indonesia's Lion Air and Corendon Dutch Airlines, cram more than 200 seats into their Max 9s, so they must have extra emergency exits. However, Alaska Airlines and United Airlines configure their 737 Max 9s to have fewer than 180 seats, so the planes don't need the two mid-cabin exits to comply with U.S. evacuation rules.
On Alaska and United, the only two U.S. airlines using the Max 9, those side exits near the back of the plane are replaced with a permanent plug the size of an exit door.
No. Boeing also makes bigger versions of its 737-900 — a predecessor to the Max — and the Max 8 with space for extra exits in the back. Buyers of those planes also may opt to have either exit doors or plugs installed.
A spokesman for Spirit AeroSystems — which is unrelated
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