NTSB Update: All 12 Door Plug Stops Failed, Leading to Blowout

DALLAS — NTSB chair Jennifer Homendy commenced the final on-site report of the day by discussing the activities of the survival factors group and the findings of the structures group.

In their investigation, the survival factors team interviewed the remaining flight crew members, and their testimonies aligned with those of the other FAs. The crew members were unaware of the situation unfolding and were primarily focused on the well-being of the passengers. Once again, the lack of communication proved challenging for the FAs, considering the seriousness of the events in the cabin.

During the explosive decompression, the cockpit door flew open, hitting the lavatory door, which got stuck due to the blow, and an FA was able to shut the cockpit door on the third try. The NTSB chief said that the cockpit door was designed to open during rapid decompression.

However, no one among the flight crew knew that. Therefore, Boeing will need to update that information for its airline customers.

What About the Decompression Warning Light Issue on Previous Flights?

The systems group focused on the cabin pressure control system. The system is designed as a triple redundant control system with one primary cabin controller, a secondary computerized controller, and a third manual one.

The NTSB chair stated that the redundant systems functioned as intended in the three previous incidents. Therefore, the NTSB concluded that there was no evidence of a connection between the previous instances of the auto-pressurization light coming on and the plug expulsion and rapid decompression that occurred during Flight 1282.

Furthermore, Alaska Airlines' (AS) internal policy restricts aircraft with multiple maintenance writeups from flying ETOPS flights as an extra safety step. This is the reason the aircraft was not allowed to fly to Hawaii—the airline implemented the restriction as a precautionary measure and for maintenance purposes.

The NTSB is still looking for the bottom fitting and spring, but both pieces are not key components for the investigation. The community members did find a plastic window and a headrest.

Mid Cabin Exterior Plug NTSB. Photo: NTSB

So What Broke?

The structures group examined the right door plug in its installed position and found no discrepancies. Everything was in place. Tomorrow they will do a 3D scan of the left opening and match it up to models so they don't miss anything, and they will send the recovered components to the lab for further examination.

Structures group engineer Klint Crookshanks took center stage to explain how the door plug is retained in the opening of the fuselage. The door plug is attached in place when 12 stop pads on the door frame interface with 12 stop pins on the door plug to prevent it from blowing out of the fuselage.

To install the door plug into the fuselage, it is rotated up so that the plug stop fitting is above the door stop pad—"it translates inward and down so the stops engage." Consider the scenario of replacing batteries on your remote control. To close the battery compartment, you would typically slide the battery cover inward and then upward.

Four stop bolts are installed in the mechanism to prevent that door plug from translating upward, essentially disengaging those stops and freeing the door plug—think of these as the screws that keep your remote battery cover in place. There are also guides for fitting the plug correctly in place. The guide rollers are installed on the fuselage, while the guide tracks are on the plug.

The structure group's exam to date showed that the door did translate upward, meaning all the stop pads became disengaged, fracturing the fittings and allowing the plug to blow out of the fuselage.

Finally, the NTSB investigator said they did not know if there was evidence that the four bolts were there or if they came out during the violent decompression event, but lab results should shed light on the matter by microscopically examining the hinges where the bolts would have been attached.

The NTSB investigation into Flight 1282 can take 12 to 18 months.

Note: The NTSB chair introduced the media briefing with a time-stamped account of the events as they unfolded on Flight 1282, which you can watch in the video below.