NTSB Investigates Door Plug Bolts in Alaska Airlines 737-9 Incident

Credit: AP. Copyright: National Transportation Safety Board

The National Transportation Safety Board (NTSB) is focusing on the bolts of a door plug assembly in its investigation of a recent incident involving an Alaska Airlines Boeing 737-9. On January 5, the aircraft experienced a critical failure when an exit door plug pivoted up and broke away mid-flight, causing rapid cabin decompression. This event occurred just minutes after the plane's departure from Portland, Oregon.

NTSB's preliminary findings indicate that the door plug, designed to remain fixed in place during normal operations, became unsecured. The plug, consisting of 12 stop fittings and held by bolts in its hinges and guide roller assemblies, disengaged from its position, suggesting a failure in the bolts — either due to them working loose or not being installed at all.

The incident's timeline, as detailed by NTSB Chair Jennifer Homendy, reveals that Alaska Flight 1272 reached an altitude of 14,800 feet when the cabin pressure dropped abruptly, signifying the plug's dislodgement. Despite the emergency, the aircraft continued to climb for about 50 seconds, reaching 16,320 feet before descending rapidly for an emergency landing in Portland. Fortunately, all 171 passengers and six crew members were unharmed.

This occurrence has prompted the FAA to mandate immediate inspections of similar 737-9 plug assemblies across various airlines. While it's too early to determine if this incident indicates a wider issue within the fleet, preliminary inspections by Alaska and United Airlines have already uncovered loose bolts and other discrepancies.

Boeing has provided detailed instructions approved by the FAA for these inspections, ensuring a standardised approach across affected airlines. As a precautionary measure, all 737-9 aircraft with this specific plug configuration remain grounded pending thorough inspections.