Alaska B39M at Portland on Jan 5th 2024, emergency exit plug and panel separated in flight

Last Update: August 6, 2024 / 18:43:55 GMT/Zulu time

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Incident Facts

Date of incident
Jan 5, 2024

Classification
Accident

Airline
Alaska Airlines

Flight number
AS-1282

Departure
Portland, United States

Destination
Ontario, United States

Aircraft Registration
N704AL

Aircraft Type
Boeing 737-900MAX

ICAO Type Designator
B39M

An Alaska Airlines Boeing 737-9 MAX, registration N704AL performing flight AS-1282 from Portland,OR to Ontario,CA (USA) with 171 passengers and 6 crew, was climbing out of Portland's runway 28L when one of the cabin windows/emergency exits and its holding panel as well as parts of one un-occupied seat (seat row 26) separated from the aircraft, the passenger oxygen masks were released. The crew donned their oxygen masks, stopped the climb at about 16,000 feet, declared emergency reporting depressurization of the aircraft in a very noisy transmission, initiated an emergency descent to 10,000 feet and returned to Portland for a safe landing on runway 28L about 20 minutes after departure. No injuries are being reported. An emergency exit and whole panel at the left hand side of the aircraft was missing.

A replacement Boeing 737-900 registration N263AK reached Ontario as flight AS-9233 with a delay of about 6.5 hours.

The NTSB have opened an investigation into the occurrence.

Passengers reported a boy sitting in row 26 had his t-shirt sucked off him while his mother was holding on to him to prevent him being sucked out, too. Several phones were sucked out as well.

The area of the panel blown out features an emergency exit for high density configuration, however, is not used as emergency exit by Alaska Airlines, the exit door was covered by a panel inside the cabin to prevent access to the release mechanism.

Alaska Airlines reported that as a precautionary measure they have grounded all their 65 Boeing 737-9 MAX aircraft. The aircraft carried 171 passengers and 6 crew when it experienced an "incident" shortly after departure from Portland.

The occurrence aircraft had entered service with Alaska Airlines on Oct 31st 2023.

On Jan 6th 2024 the FAA announced an emergency airworthiness Directive will be released requiring in total 171 Boeing 737-9 MAX aircraft to be inspected before they can return to service. The inspection will take between 4 and 8 hours per aircraft.

On Jan 6th 2024 the airline reported about 25% of their 65 aircraft have already been inspected without any findings, the fleet is expected to be back in the air soon.

According to the FAA database the occurrence aircraft received its first airworthiness certificate (after production) on Oct 25th 2023.

On Jan 6th 2024 (US time, Jan 7th UTC) the NTSB stated in a media briefing, that John Lovell, who participated in the investigation into the crash of the Ethiopian Boeing 737-8 MAX (see Crash: Ethiopian B38M near Bishoftu on Mar 10th 2019, impacted terrain after departure, will be the lead investigator in the NTSB investigation into the occurrence. A mid cabin door plug departed the aircraft resulting in rapid decompression. The aircraft was certified up to 189 passengers, thus the aircraft did not need to have emergency exit doors at that location, the airline actually has 178 passenger seats only. The black boxes of the aircraft will be sent to the laboratory for analysis. The aircraft was at about 16,000 feet and about 10 minutes into the flight when the door plug blew out, fortunately the aircraft was not at FL300 or above. The NTSB needs the help of the public to locate the door plug, the NTSB believes from radar data that the door plug may be between Barnes Road and I-217 in the Cedar Hills neighbourhood. If parts are being found, contact local authorities like police. The aircraft had been delivered to Alaska Airlines on Nov 11th 2023. The "stop portions" are still intact at the door. The plug is not an operational door, it could be opened from the outside for an inspection though. Another media briefing is estimated to be held on Jan 8th 2024.

On Jan 7th 2024 the FAA released their Emergency Airworthiness Directive EAD 2024-02-51 requiring all Boeing 737-9 MAX aircraft certified in any category with mid cabin door plugs installed to be inspected upon receipt of the EAD, the operation of the aircraft is prohibited until that inspection is completed. Special flight permits are available for unpressurized flights only. The FAA reasons: "This emergency AD was prompted by a report of an in-flight departure of a mid cabin door plug, which resulted in a rapid decompression of the airplane. The FAA is issuing this AD to address the potential in-flight loss of a mid cabin door plug, which could result in injury to passengers and crew, the door impacting the airplane, and/or loss of control of the airplane."

On Jan 7th 2024 (Jan 8th UTC) the NTSB held another media brief (see below). On Dec 7th 2023, Jan 3rd 2024 and Jan 4th 2024 an auto-pressurization fail light illuminated in three flights, the switch was flipped to alternate mode and the flight continued. The light was reported, maintenance tested and reset and returned the aircraft to service. There is no knowledge yet of whether there is a correlation to the separation of the door. As result of the light Alaska Air did not use the aircraft for ETOPS operations to Hawaii. As result of the door plug separation there was a lot of interior damage to panelling, trim, windows (internal plastic window panes, seal still intact), seat rows 33, 32, 31, 27, 26, 25, 12, 11, 4, 3, 2 and 1 were affected. In seat rows 26 and 25 there was also damage to the seats, 25a missing its headrest, 26a was torqued missing its headrest, back panel and tray table at its back. Seats 26a and 26b were unoccupied during the accident flight. The Cockpit Voice Recorder was completely overwritten, when circuit breaker was not pulled. Portions of the flight data recorder were used to narrow the search area for the door plug and phones. During the explosive decompression the cockpit door flew open as designed and impacted the forward lavatory door shutting it jammed, there were concerns somebody might have been trapped in the lavatory, nobody was in the lavatory at that time however. Quote by the NTSB chairwoman: "I just really want to we want we want to thank the actions of the flight crew that that was equally heroic the just the flight crew entirely did an excellent job thank you for that um along with well." The emergency exit plug has not yet been found, it's colour is yellowish green. Two mobile phones were found by members of the community and handed in.

In the afternoon of Jan 8th 2024 the NTSB announced that the missing door plug has been located and recovered. It is being sent to Washington for further examination.

On Jan 8th 2024 United Airlines reported they have found loose bolts in door plugs of a number of their Boeing 737-9 MAX aircraft. The bolts needed tightening.

On Jan 8th 2024 (Jan 9th UTC) the NTSB reported in their last media briefing on site that according to the FDR the aircraft was climbing through 14,830 feet MSL at 271 KIAS when the cabin pressure reduced from 14.09psi to 11.64psi and the cabin altitude 10000 feet warning activated, a second later the master caution activated and the cabin pressure fell to 9.08psi at about 14850 feet MSL and 271 KIAS. 18 seconds later the master caution deactivated, the aircraft stopped the climb at 16,320 feet about 82 seconds after the pressure fell to 9.08psi at 276 KIAS. The selected altitude changed from 23,000 feet to 10,000 feet and the aircraft began a left turn, the aircraft descended through 10,000 feet 5:29 minutes after the pressure dropped to 9.08psi. The cabin altitude warning ceased when the cabin pressure increased to 10.48psi and the aircraft returned to Portland for landing on runway 28L. No one amongst the flight crew knew that the cockpit door was designed to open in case of a rapid decompression, Boeing is going to make changes to the manuals. All passenger oxygen masks deployed as designed but a number were later stowed back up into their compartments. When the auto-pressurization light came on on Jan 3rd and Jan 4th, the pilots did not need to go into manual mode but just switched the cabin pressure controller, there is no evidence that those events were related to the door plug. This is going to be reviewed again by a Boeing specialist. A school teacher and his students were a "hit at school today" when they discovered the door plug, the NTSB retrieved the door plug. The NTSB is particularly looking at the bottom hinge fitting and large spring there. A plastic window frame as well as a head set was also found. The right hand door plug was found entirely without discrepancies. The door plug - no door installed - is put into place using 12 stop pads. 4 bolts would then be engaged to keep the door plug in place. However, the plug translated upwards disengaging all 12 stop bars, the 4 bolts have not been found, there is no information whether they were present or not yet, this is going to be subject of examination at the labs.

On Jan 9th 2024 Alaska Airlines reported a number of their B39M aircraft showed loose parts during the inspections following the door plug separation, too.

On Feb 6th 2024 the NTSB released their preliminary report summarizing the sequence of events:

Both flight crewmembers held airline transport pilot (ATP) certificates. The captain had accumulated about 12,700 hours of flight experience, of which about 6,500 were in the accident airplane make and model. The first officer (FO) had accumulated about 8,300 hours total flight experience, of which about 1,500 were in the accident airplane make and model.

The captain was the pilot flying and the FO was the pilot monitoring. The flight crew stated that the preflight inspection, engine start, taxi, takeoff, and departure climb were unremarkable.

After takeoff, the flight crew checked in with Seattle Air Route Traffic Control Center and was cleared to flight level (FL)230 [23,000 feet]. The captain said that, while climbing through about 16,000 ft, there was a loud bang. The flight crew said their ears popped, and the captain said his head was pushed into the heads-up display (HUD) and his headset was pushed up, nearly falling off his head. The FO said her headset was completely removed due to the rapid outflow of air from the flight deck. Both flight crew said they immediately donned their oxygen masks. They added that the flight deck door was blown open and that it was very noisy and difficult to communicate.

The flight crew immediately contacted air traffic control (ATC), declared an emergency, and requested a lower altitude. The flight was assigned 10,000 ft. The captain said he then requested the rapid decompression checklist, and the FO executed the required checklist from the Quick Reference Handbook (QRH). As the FO completed the checklist, the captain flew the airplane as they coordinated with ATC to return to the PDX airport. The flight landed on runway 28L without further incident and taxied to the gate.

The NTSB reported: "The two vertical movement arrestor bolts, two upper guide track bolts, forward lower hinge guide fitting, and forward lift assist spring were missing and have not been recovered." and continued: "Contact damage was noted on the lower sides of the 12 stop pins and fittings on the MED plug. Corresponding contact damage was noted on the 12 stop pads and fittings attached to the fuselage. Overall, the damage was consistent with the MED plug translating upward, outboard, and aft during the separation." and further stated: "Overall, the observed damage patterns and absence of contact damage or deformation around holes associated with the vertical movement arrestor bolts and upper guide track bolts in the upper guide fittings, hinge fittings, and recovered aft lower hinge guide fitting indicate that the four bolts that prevent upward movement of the MED plug were missing before the MED plug moved upward off the stop pads."

The NTSB continued:

The Manufacturing Records Group traveled to Boeing’s Renton, Washington, facility to review manufacturing records for the accident airplane specific to the left MED plug area. According to records, the accident fuselage arrived at Boeing’s Renton facility by rail on August 31, 2023. During the manufacturing process, if any defects or discrepancies were found, a Non- Conformance Record (NCR) or a disposition required NCR were generated.

On September 1, 2023, records show that NCR 1450292531 was created noting five damaged rivets on the edge frame forward of the left MED plug. See figure 14 for rivet locations.

Documents and photos show that to perform the replacement of the damaged rivets, access to the rivets required opening the left MED plug (see figure 15). To open the MED plug, the two vertical movement arrestor bolts and two upper guide track bolts had to be removed.

Records show the rivets were replaced per engineering requirements on Non-Conformance (NC) Order 145-8987-RSHK-1296-002NC completed on September 19, 2023, by Spirit AeroSystems personnel. Photo documentation obtained from Boeing shows evidence of the left-hand MED plug closed with no retention hardware (bolts) in the three visible locations (the aft upper guide track is covered with insulation and cannot be seen in the photo). See figure 16. This image was attached to a text message between Boeing team members on September 19, 2023, around 1839 local. These Boeing personnel were discussing interior restoration after the rivet rework was completed during second shift operations that day.

The investigation continues to determine what manufacturing documents were used to authorize the opening and closing of the left MED plug during the rivet rework.

The Human Performance Investigator joined the group to travel to Spirit AeroSystems, where they reviewed pertinent build work documents and observed a door plug installation. As mentioned earlier, the accident MED plug was manufactured by Spirit AeroSystems Malaysia on March 24, 2023, and received at Spirit AeroSystems Wichita on May 10, 2023. The MED plug was then installed and rigged on the fuselage prior to delivery to Boeing. During the build process, one quality notification (QN NW0002407062) was noted indicating the seal flushness was out of tolerance by 0.01 inches. No manufacturing rework was required, as Spirit AeroSystems Engineering determined the condition was structurally and functionally acceptable and did not adversely affect the form, fit, or function of the installation. There were no other QNs for the left MED plug before leaving Spirit AeroSystems. Fuselage Line 8789 was shipped to Boeing on August 20, 2023.

The group then traveled to AAR, Oklahoma City, where a wi-fi and PCS antenna was installed on the accident airplane from November 27, 2023, to December 7, 2023. The group reviewed applicable installation retrofit documents and received a presentation on AAR’s quality assurance and safety management system (SMS) processes. The group also witnessed a wi-fi retrofit in progress. Facility representatives reported that they have modified approximately 60 Alaska Airlines 737-9 airplanes with the wi-fi and PCS antenna installation and have not had to remove or open any MED plugs for this work, to include the event airplane.

The manufacturing/human performance group has done a complete records review from the time the event airplane left the Boeing factory to the time of the accident and found no evidence that the left MED plug was opened after leaving Boeing’s facility.

On Aug 6th 2024 the NTSB released their public docket into the accident and held a hearing into the accident.

The NTSB media briefing of Jan 8th 2024:

The NTSB media briefing of Jan 7th 2024:

The NTSB media briefing of Jan 6th 2024:

Figure 14 Photo on the left shows the five locations of the damaged rivets. Photo on the right is a close-up of a damaged rivet. (Source: Boeing. Image Copyright © Boeing. Reproduced with permission.):

Figure 15 Photo showing the MED plug opened to work on damaged rivets. (Source: Spirit AeroSystems.):

Figure 16 Photo showing the left MED plug immediately before interior restoration and the circles show the three locations without the retaining bolts, two vertical movement arrestor bolts and the forward upper guide track bolt. The aft upper guide track is covered with insulation and cannot be seen in the photo. (Source: Boeing. Image Copyright ©