Boeing's "Safe Decompression" Design Philosophy and
The Aloha Flight 243 Accident

1. Boeing designed the 737 and 727 fuselage using a concept called "safe decompression". This concept says that regular detailed inspection of the fuselage is NOT required because failure of any part will be "damage obvious or malfunction evident", the damaged area can grow so big that it is obviously noticeable before compromising the structural integrity of the fuselage in flight. This obvious damage includes blowing a 10"x10" hole in the fuselage, inflight, causing a "safe decompression".

2. Boeing designed and the FAA approved of the concept such that it is perfectly acceptable to fly a 737 without close inspection until a 10"x10" hole blows open at altitude. The main focus of the NTSB Aloha Hearings was "Why did the 737 not flap (blow a hole)?"

3. The question of the day at the Aloha Hearings was "Why didn't it flap?" The true answer was, it did, exactly as planned and designed. The correct question that was never asked (or answered) during design, testing, certification, accident investigation, etc. was "What happens if the airplane does open a 10"x10" hole at 24,000 feet altitude, the air inside the plane starts to escape [@ appx. 700 mph] and then, something plugs the hole, such as seatback, suitcase or ... human body?"

4. The Answer to the correct question is inflight disintegration. When the hole opens in the fuselage, the cabin air begins escaping at approximately 700 mph through the opening. Every molecule of air inside the cabin senses the chance to escape and begins moving toward the opening.

5. In the Aloha incident, the flight attendant was standing under the hole when it opened. She was sucked by the 700 mph escaping jetstream into the 10"x10" hole and plugged it. What blew the roof off the airplane was the resulting "Fluid Hammer" caused by slamming shut the door on a 700 mph jetstream. The already structurally degraded fuselage (89,680 flights vs. 75,000 designed) easily succumbed to the huge momentum of the rapidly escaping mass of cabin air with no place to go.

6. This was the SECOND 737 to disintegrate in the same manner. A Far Eastern Air Transport(FEAT) 737 came apart at 23,000 feet over Taiwan within 1981. The FEAT and Aloha aircraft were virtually identical being Boeing Production Line Numbers 151 and 152, respectfully. The official cause of the FEAT accident was "lower lobe decompression" [blew a hole out the bottom]. However the flight data recorder indicated a negative 4 G-force swing in one second during the initial phase of the accident. This evidence was dismissed because "According to the aircraft characteristics, this variation is impossible to occur in 1 second." [this plane can't do that]. There was no indication the data recorder was faulty. Also, a lower lobe decompression would have thrown the nose of the plane up and recorded a POSITIVE G-force indication. As shown by the G-force analysis accessed through this link a flapping/fluid hammer incident on the upper S-4 lap joint would have given almost exactly the G-force value recorded.

7. The difference between the Aloha and the FEAT accidents was thoroughly addressed (literally frame number by frame number) by a Mr. Norman Jensen and sent to the NTSB in Sept. 1988. On the FEAT aircraft the initial flap was on the top of the airplane, which buckled all the floor beams and broke all the control cables such that the pilot could not recover. On the Aloha aircraft, the initial flap was on the left side, which buckled the left floor beams and broke the left control cables, but the pilot was still able to bring the plane in on the right engine minus an 18' section of the upper fuselage and one flight attendant.


1. There is not a design flaw in the structure of 737 fuselage. There is a flaw in the DESIGN PHILOSOPHY of the 737 fuselage. The fuselage may be successfully designed such that blowing a 10" hole at altitude may not affect the residual structural integrity to the point of total loss of the aircraft. However, anyone sitting near the "safe decompression" site will suffer barotrauma (ruptured ear drums, etc.), the turmoil of inflight decompression could easily induce heart attacks in elderly passengers, the list goes on. Would any airline passenger willingly board a plane knowing a "safe decompression" was going to occur on "this" flight? Yet the 737 is Boeing designed and FAA certificated to fly until it does blow a hole at altitude, defined as "obvious failure".

2. The introduction of a Fluid Hammer effect into the "safe decompression scenario" eliminates the "safe" in the 737 design philosophy. Not one, but two 737s have suffered catastrophic inflight disintegrations due to the fluid hammer effect and both investigations failed to determine the true cause of the failure. Consequently, proper corrections have not been made to the system to eliminate recurrence.