Alaska Airlines Is Shown the Door

Boeing’s 737 Max series just can’t get no respect. Back in the pre-pandemic world, the Max 8 was grounded for more than two years after a series of fatal crashes in 2019. Now the Max 9, the next iteration of the classic workhorse airliner has its own problems after an Alaska Airlines plane lost a door in flight.

Let’s start with the basics. This is an airplane.

Photo by Frank K. from Anchorage, Alaska, USA, CC BY 2.0 , via Wikimedia Commons

Okay, maybe we don’t need to go that basic. But the picture above is the actual aircraft involved in the incident, a 737 Max 9 that first flew on October 15, 2023, and had only completed 145 flights.

Returning to the basics, jet airliners typically cruise at altitudes in the 30,000 to 40,000-foot range. The air is much less dense at those altitudes than at the surface. To allow the airplane’s occupants to breathe, airplanes are pressurized with engine bleed air. This is air that is tapped from the engine and diverted through a pressurization and air conditioning kit (PACK) to make it safe and comfortable for people to breathe and then piped into the cabin.

Some aircraft that fly at high altitudes without pressurization use oxygen masks to supply the passengers and crew, but this is only effective to a certain point. As airplanes fly higher, the air becomes so thin that the body cannot absorb oxygen from a mask. For this reason, unpressurized airplanes rarely fly above 25,000 feet.

Pressurizing an airplane means that there is a lot of force pushing out from the highly pressurized cabin to the lower pressure outside. This pressure is immense. At 30,000 feet, the pressurization applies a force of about 7.8 pounds per square inch of the fuselage. That force would be multiplied by the total area of an aircraft door.

The door on the Max 9 measures 26 by 46 inches for a total area of 1,196 square inches. That means that the total force on the door was about 9,329 pounds. (I’m not a math whiz so if my math is off, please don’t hold it against me.)

The practical effect of this bit of trivia is that it would be physically impossible to overcome 9,000 pounds of pressure and pull a door open if it opens to the inside. The flip side is that there is a lot of pressure pushing outward on doors and windows so they have to be strengthened. This is particularly tricky with doors, which by their nature are designed to opened and closed.

One way that designers solve this problem is by making the door plug into a hole in the fuselage. If the door is smaller than the hole, it can never be blown out unless either the door or the fuselage has a structural failure.

The second design involves using hardware to keep the door shut. My corporate jet uses locking pins that are inserted into the door to keep it shut, but the door on the 737 Max 9 uses bolts to hold the door shut. An NTSB post to the platform formerly known as Twitter shows a schematic of the door, which opens downward on a hinge. Two arrestor bolts prevent the door from moving upward over a guide track that requires the door to move upward to open. There is a detailed video on YouTube that shows the door and its operation. If you’re interested enough to spend 17 minutes on a 737 door, I salute you.

An interesting detail from the video is that the door on the Max 9 is a plug door. In this context, that means that the door is covered over by the cabin interior and not visible from the inside. In other words, it plugs a hole rather than being a functioning door. To passengers, it would appear to be a normal row of seats rather than an exit row. This configuration is only available on the Max 9 and is used to increase the number of passenger seats.

The investigation is ongoing, but the FAA ordered inspections of the doors on other 737 Max 9s, and United Airlines reported finding loose bolts on a number of its aircraft. The report from ABC News does not detail how many loose bolts were identified or exactly what kind of bolts they were. Alaska also reportedly found more problematic “hardware” on its planes.

In the case of Alaska 1282, the airplane was reportedly climbing through 16,000 feet about 20 minutes after takeoff when the door gave way. What would happen in this situation is that there would be an initial loud noise and rushing of wind as the air contained in the cabin rushes out. It would also carry papers and small, unsecured objects. After the initial blowout, passengers would be subjected to wind and engine noise for the remainder of the flight, much like driving a car with the windows open. The temperature would also fall rapidly as due to cold temperatures at high altitude. Oxygen masks would drop from the ceiling (i.e. the “rubber jungle”), but most people could breathe without them for a short time at 16,000 feet. The time of useful consciousness without supplemental oxygen is about 30 minutes at 16,000 feet but falls to 15-20 seconds at 40,000 feet.

A passenger recorded the scene with his phone:

Thankfully, no passengers were sitting in the row next to the door, but a child’s shirt was reportedly ripped off by the decompression. There were no serious injuries but three minor injuries were reported. These could have been ear or sinus injuries from the rapid decompression.

Emergency descents after a rapid decompression are a standard emergency item that pilots practice in the simulator. While the procedure varies from airplane to airplane, the general strategy is the same: To rapidly fly the airplane to an altitude where the air is thicker. This might include a descent rate of up to 10,000 feet per minute, but given the low altitude of the Alaska incident, such a high rate of descent would not have been necessary.

The emergency descent procedure is usually a memory item that includes donning oxygen masks, pulling throttles to idle, and deploying speed brakes. Notifying air traffic control of the emergency is also a priority.

There have been other rapid decompression accidents in the past. Two of the most well-known are Aloha Airlines Flight 243 in 1988 and Southwest Fight 1380 in 2018. In each of those cases, one passenger was killed. Interestingly, both of those accidents also involved 737s although the exact model and cause were different in each of the three accidents.

The strangest thing about Alaska 1282 is the fact that the airplane was almost brand new. In contrast, the other two 737 decompressions were in airplanes that had been flying for far more than a decade.

Together with the revelations about loose bolts on other 737 Max 9s, the evidence seems to point to a manufacturing problem. This could be a problem with the design of the door, the quality of the bolts, the assembly process, or something entirely different. This will undoubtedly be another blow to Boeing’s reputation, which took a hard hit from the 737 Max 8 scandal.

Another famous decompression accident occurred in 1990 when the cockpit windshield of British Airways Flight 5390 blew out at 17,000 feet, sucking the captain out. The first officer managed to hold on to the captain and successfully land the plane with no fatalities. The cause of that accident was determined to be that maintenance personnel had installed the wrong size bolts. (The accident chain is longer than just that one mistake. Tim Harford discussed the errors in an episode of “Cautionary Tales,” one of my favorite podcasts.)

With the attention being paid to the bolts on 737 doors, passengers can be confident that there probably won’t be a repeat of the Alaska 1282 accident. However, the lesson here is that it’s a good idea to keep your seatbelt fastened whenever you are in your seat on an airliner. Even if the seatbelt sign is off, the plane can experience sudden turbulence (it isn’t uncommon for unbuckled passengers to be injured by turbulence) or a structural issue that leaves the cabin open to the outside world. If passengers had been sitting in the row next to the door without the seatbelt, they would have been sucked out of the hole before they had time to react. It’s a long way down from 16,000 feet.

And as I wrote last week about the recent Japan Air Lines collision, pay attention to the flight attendants when they give the safety briefing. Airline flying is statistically safer than the drive to the airport, but if things go sideways, it can happen quickly. Your life can depend on small details such as whether your seatbelt was fastened or if you remember the color of the lights that indicate the exit row.