Boeing 737
This is the most successful aircraft ever manufactured. It has sold more than 10,000 airframes. Early decisions in its lifespan eventually caused difficulties in variants that no one expected. For example, there was a decision to mount the engines below the wing. That had been preceded by a decision to mount the wings low on the fuselage. There was only so much room available to bend the aircraft.
Some customers wanted more speed, which required new engines. Some customers clamored for greater fuel efficiency, which had several solutions, all of which required changes to engines or wings.
MAX Crashes
Boeing attempted to do both simultaneously. Changing the wings was out of the question. See below. It was an ambitious program. With more powerful engines using less fuel, the handling characteristic of the aircraft changed. There were two fatal crashes: Lion Air an Indonesian airline on October 29, 2018, and Ethiopian Airlines on March 2, 2019. There were no crashes or other problems involving US, European or Japanese aircraft.
When I pointed this out, I was accused of racism. I was claiming that pilots of color were not as good as white pilots. Poppycock. US, UK, Japan and most European airlines required pilots have 1,500 hours of flight experience; the two airlines required only 150. There were problems with the flight control software, which seems to have been the cause of the two accidents in question. Pilots with more experience were better able to sort out workarounds on the fly than those with less experience.
Why am I writing about this now?
Earlier this month an Alaska Airlines 737 MAX 9 experienced an in-air blowout of a door plug, a piece of fuselage inserted to replace a door which had been removed. There were neither fatalities nor injuries, nor any other damage. The earlier issues with the 737 MAX aircraft raised questions about the safety of the aircraft. Alaska entrusted the aircraft to Boeing to fix the problem, which was insufficient tightening of the bolts.
Aircraft are often described as thousands of parts flying in close formation. That is fairly accurate. I learned from an aircraft fastener manufacturer that the number of fasteners is not specified by the original equipment manufacturer. That is left to the manufacturing engineers working on the assembly line.
A few words about building aircraft might help here.
Building Aircraft
The wing is the aircraft. It is the most important part of the machine. The fuselage, inside of which passengers fly, is fairly useless except for something on which to hang more important parts. Designing the wing is the most complex and expensive part of the process. Every night Boeing trucks multiple Teradata of information over a mountain range to a site not vulnerable to the same risks as the coast. The underside of the wing is flat, while the upper side is curved. As the aircraft moves through the air, the air on the underside of the wing moves slower than the air on the upper side. That creates a partial vacuum above the wing, which sucks the airplane upward. This is known as lift.
The wing is designed to be attached to the fuselage at a specific point for the lift to be calculated. Moving the wing attachment point requires redesigning the wing. In the long run it would be cheaper to design a replacement aircraft. Boeing’s only real competitor, Airbus, solved the issues differently. It began with the A320 and built variants forward and back. The backwards variants were easy: slice through the fuselage, take out a few feet, reseal the fuselage. Thus, an A319 and an A318 were born.
Going forward had different issues. Making the aircraft longer meant possibly duplicating the Boeing MAX problems. Fortunately, Airbus had positioned the wing higher on the fuselage than Boeing did for the 737. The Airbus A721 had no “MAX” problems. Even when it was re-engined to increase efficiency and reduce noise, this Airbus 721neo was a winner compared to Boeing.
Wings
The wing has moveable attachments at the front and the back. The front of the wing (called the leading edge) has slats which can be extended to provide additional lift at slower speeds and lower altitudes. The back of the wing (called the trailing edge) has ailerons that move up and down. The wing typically moves in the direction of the ailerons. The wingtips dispel tiny tornados that form naturally at the edge of the wings. There are also “spoilers” in the wing that help to “spoil” lift when it is time to descend or land. The wings typically serve another purpose. Most contain fuel to run the aircraft engines. In the case of some military aircraft, such as the F/A-18 (largely used on aircraft carriers) there is a “wet tail,” meaning that the vertical stabilizers at the rear of the aircraft are also filled with fuel.
Alaska Airlines
The impetus for this article was the Alaska Airlines 737 MAX9 that lost a door plug mid-flight. The final message: you can trust US, Japanese and European flight deck crews to get you from place to place safely. Otherwise, it’s Caveat Emptor. There’s another message for the flying public, and that concerns the cabin crew. A few airlines hire cabin crew based on age, weight, and comeliness. I don’t fly those airlines. The gold standard for cabin crew is British Airways, which qualifies cabin crew by aircraft type. If the cabin crew member hasn’t flown on that type (e.g., Boeing 747) for a month (it may be two months, I’m not current), he needs to go through training again. Almost all airlines consider cabin crew interchangeable and unimportant. I was told a story by a former British Airways 747 pilot that a BA 747 and a Singapore Airlines 747 were flying through a volcanic ash-cloud at the same time; all four engines of both aircraft shut down. The gorgeous Singapore Airlines cabin crew lost four or five passengers dead, and another dozen+ injured. The dowdy British Airlines cabin crew had no fatalities and few injured.
If there is interest, I’ll cover why no two commercial aircraft are ever identical, and the other parts of an aircraft and the two methods of assembly (assembly line and jig). Let me know what you want, please.
Assembly line vs jig please
"If there is interest, I’ll cover why no two commercial aircraft are ever identical, and the other parts of an aircraft and the two methods of assembly (assembly line and jig). Let me know what you want, please."
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Geez, Bill. I'd read 5,000 words from you on toilet paper embossing mechanisms. Anything you want to write about, I don't think any of us here would be complaining.