Boeing to retrofit 737 MAX fleet with enhanced door plug design following NTSB probe
June 26, 2025
The National Transportation Safety Board (NTSB) has urged Boeing to retrofit its 737 MAX fleet as well as new aircraft with an enhanced design for mid-exit door plugs.
The direction follows an NTSB Board meeting on 24 June which found the probable cause of the Alaska Airlines incident on 5 January 2024 to be Boeing’s failure “to provide adequate training, guidance and oversight” to its staff.
Alaska Airlines flight 1282 experienced an in-flight separation of the left mid exit door (MED) plug six minutes after take-off.
The 737 MAX 9 aircraft, which was carrying 171 passengers, was climbing at about 15,000 feet when the incident happened, causing rapid depressurisation.
Passengers’ belongings were sucked out of the airplane, oxygen masks dropped and the door to the flight deck swung open. One flight attendant and seven passengers received minor injuries, while the aircraft sustained substantial damage.
Today marks one year since a door plug blew out of Boeing aircraft during an Alaska Airlines flight
— Morning Brew ☕️ (@MorningBrew) January 5, 2025
Boeing's 12 months since…
• Stock is down 31%
• Numerous mechanical issues
• Seven-week strike by machinists
• Kelly Ortberg replaced Dave Calhoun as CEO pic.twitter.com/Q673rfCT7u
Alaska Airlines temporarily grounded its fleet of 737 MAX 9 aircraft to inspect other plugs, but this was determined to be an isolated incident.
NTSB: Missing bolts caused plug blowout
Following the incident in 2024, subsequent analysis found that during final assembly at Boeing’s Renton facility in the US, four securing bolts were never reinstalled in the panel after it had been removed for repair work.
The NTSB’s report determined that “when the airplane was manufactured, Boeing personnel had opened the left MED plug (which inherently required removing the four bolts and associated hardware) to allow access for rivet rework to be performed.”
According to NTSB chair, Jennifer Homendy, a cascade of systemic failures led to the incident rather than it being down to individual misconduct.
“The safety deficiencies that led to this accident should have been evident to Boeing and the Federal Aviation Administration (FAA) – and should have been preventable,” said Homendy.
NTSB also found that despite opening an MED plug being a nonroutine task “no personnel experienced with opening or closing an MED plug were on duty at the time’s that the accident airplane’s left MED plug was opened and closed.”
NTSB Blames Boeing for Alaska Airlines 737 MAX 9 Door Plug Blowout ✈️
— AirNav Radar (@AirNavRadar) June 26, 2025
The U.S. National Transportation Safety Board (NTSB) has determined that Boeing’s failure to follow critical safety protocols directly led to the dramatic mid-exit door (MED) plug blowout on Alaska Airlines… pic.twitter.com/1YSvNguypn
While a removal record should have been documented for the opening of an MED plug, no such record was generated. “The left MED plug was subsequently closed without its securing bolts and attachment hardware, and no quality assurance inspection of the plug closure was performed,” according to NTSB’s report.
It also found that “Boeing’s Business Process Instruction (BPI) for performing parts removals lacked the clarity, conciseness and ease of use necessary to be an effective tool for workers in the manufacturing process.”
FAA failure to detect repeated discrepancies
In addition, Boeing’s on-the-job training for removal records was found to be insufficient, while the Federal Aviation Administration’s (FAA’s) inspections and audits also failed to detect repeated discrepancies in Boeing’s parts-removal process, partly due to a policy of discarding records older than five years.
Design enhancements complete
Speaking during NTSB’s Board Meeting, safety investigator and engineer Clint Crookshanks explained that Boeing and supplier Spirit AeroSystems (which Boeing is in the process of acquiring) have completed engineering work for a design change to 737 MAX mid-cabin door plugs.
Designed for installation on all MED plugs, Crookshanks explained the enhancement “adds secondary hammer shaped retention devices to the forward and aft sides of the plug.”
To ensure the devices “engage with the fuselage and prevent vertical translation of the plug, these retention devices must be rotated into position when completing the installation,” Crookshanks continued.
Furthermore, these retention devices have been designed to prevent installation of the cabin sidewall panels unless they are properly engaged.
The enhancement also includes the installation of lanyards on the two upper guide track bolts and the two vertical movement arrestor bolts. This will “permanently secure the bolts to the plug” and “provide a visual indication” of whether they have been installed correctly, added Crookshanks.
When will the enhancements be installed?
With the design enhancement now complete, Boeing is progressing certification planning and compliance work and expects to start equipping new jets with the design enhancement in 2026.
In-service aircraft will be retrofitted following the issuance of a service bulletin.
The NTSB is also recommending Boeing revise its BPI for parts removal to include “clear and concise guidance for determining when a removal record is needed” and to ensure relevant and recurrent training is in place for manufacturing personnel.
“We also recommend that Boeing develop a process that can identify escapes that result from human error, assess them using a system specifically designed to identify factors that contribute to such errors and implement effective mitigation strategies.”
NTSB’s investigation also highlighted the need for additional training on flight crew oxygen masks and their communication systems.
