A dangerous flaw in the original 1960s design of the Boeing 737, thought to have been eliminated, will be the focus of the investigation into the emergency that caused Alaska Airlines to ground its fleet of 65 of the latest 737 model, the MAX.
Alaska Airlines Flight 1282 from Portland, Oregon, to Ontario, Canada had been in the air for six minutes, climbing at around 300 mph when, reaching a height of 16,000 feet, a side panel of the fuselage, aligned with a row of seats, blew out. The airline reported this as an “explosive decompression”—caused by the sudden release of pressurized air inside the cabin into the far lower outside pressure.
This was an almost exact repetition of what happened to Southwest Airlines Flight 812 from Phoenix, Arizona to Sacramento, California in April 2011. In that case, the sudden explosion caused a hole in the roof of the cabin, 50 inches long and nine inches wide: Calling in the emergency to air-traffic controllers, the pilot said, “We lost the cabin.” The flight diverted to the nearest airport, Yuma, where it touched down safely but passengers recalled, as in the Alaska event, being terrified for their lives.
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In both cases, oxygen masks were automatically released so that passengers could get air until the jet reached lower altitudes below 8,000 feet where the pressure inside and outside was equalized.
On Saturday the FAA extended the grounding to other airlines operating the 737-9 Max model, a total of 171 jets, including 79 operated by United Airlines, the largest user of this model.
Following the Southwest emergency I carried out an investigation of the 737’s history for Newsweek and The Daily Beast. It uncovered a trail of similar structural failures in the fuselage of the 737–designed in the 1960s—some fatal, all very scary. Perhaps the most visually stunning example was a 737 flown by Aloha Airlines in 1988 where a huge chunk of the cabin’s wall and ceiling blew out and passengers were left fully exposed, although the pilots got the airplane down safely. The cause of that incident was metal fatigue caused by humidity.
Earlier, in 1981, a Taiwanese 737 dived from 22,000 feet after an explosive decompression, killing all 110 people on board. Investigators discovered that frozen fish, carried frequently in the cargo hold, had caused catastrophic corrosion to the skin of the fuselage.
The important point about these early examples of explosive decompression is that investigators successfully identified the causes and steps were taken to remedy them, specifically to change to stronger metal with far better anti-corrosive qualities.
When Boeing designed an extensively updated model of the 737 in the early 1990s, the New Generation (NG), it made 38 changes to eliminate structural failure as well as taking a fuselage off the production line and testing it to three times its expected life, although some safety experts told me that this test did not fully replicate the stresses on a jet that often makes as many as seven or eight flights a day. Boeing countered that it made 10 more changes as a result of the tests and were satisfied that the danger had been eliminated. As Southwest Flight 812 demonstrated, it had not.
The fuselages of the 737 MAX are manufactured by Spirit Aerosystems in Wichita, Kansas. There have been quality control problems: Last year Boeing discovered that in some fuselages the aft pressure bulkhead—critical to the prevention of decompression in the cabin—had been incorrectly assembled.
As Alaska checks every one of the grounded jets for tell-tale cracks, they will be using highly advanced scanning technology. They are looking for a deeply buried flaw that everyone had assumed had finally been eliminated.
In fact, the Alaska Airlines episode highlights a problem unique to the 737: how to carry forward engineering from the analog age in an airplane that is, in other major respects, of this era, particularly with avionics and vastly transformed, more efficient and more powerful engines.
This problem was apparent with the two fatal 737-MAX crashes, killing 346 people, that caused the entire world fleet to be grounded for 20 months. In that case the deadly problem lay in software introduced into the flight control system that overrode the pilot’s ability to correct an error in the jet’s air speed readings. The 737’s relatively cramped flight deck is crammed with new avionic aids but still requires hands-on muscle power in some situations.
As it happened, the 2011 emergency with Southwest Flight 812 occurred just as the Boeing board were deciding whether to make one more generational stretch of the 737 or finally retire the design in favor of a thoroughly transformed new model to retain a competitive edge against its rival, Airbus. The board decided to go ahead with the MAX, a decision that was to cost many billions of dollars after the two crashes.
As a result, the Airbus competitor, the A320/21 series—designed in the 1980s and far more easily updated with new engines and avionics—will dominate the market for single-aisle jets for years to come.
