Airbus A320 series aircraft drinking water system water filter design 瑕疵 (repair of screwing screws)

The reason why it is called 瑕疵 is because improper use will bring a lot of unnecessary trouble to the maintenance, waste a lot of manpower, material resources, of course, this is something we do not want to see. It is not called a defect because it does not involve security issues. There are clear definitions of design flaws in national laws, and more often it can be called design flaws only when it comes to security issues.

This is a narrative describing the work of the aircraft, not a troubleshooting article. Since it is the first article on this issue, it is more about the description of phenomena and construction methods. The two articles on this issue will focus on the theoretical analysis of reliability analysis and production optimization.

The maintenance cost of a civil aircraft is an important part of the operating cost of the aircraft. The ease of maintenance of civil aircraft is a problem that aircraft design manufacturers must be treated with caution. An excellent design scheme often brings great convenience to workers during aircraft maintenance, saving a lot of time and labor. It is not an easy task to design a good solution. It often involves many subjects such as human engineering, reliability and many other aspects.

The good and bad of design are often the result of comparison. Without children, there will be no anxiety in childhood. From another point of view, this is sometimes a good thing for everyone to improve. Today we want to compare children to one aspect of Boeing and Airbus children: water system kitchen water filter maintainability.

When we recently replaced the drinking water system kitchen water filter in the Airbus A321 aircraft inspection, we encountered a very difficult problem. The work that was completed in half an hour or even less took an afternoon plus the next day. A few hours in the morning. The time to finish the work is ten times more than expected! To clarify this story, it is necessary to understand the location of the drinking water filter in the kitchen of the Airbus A320 (different flying mechanisms, the specific location may not be consistent with the description), as shown below:

It is located behind the back kitchen coffee machine and water heater and is accessible through a panel with a "water filter inside". The water heater is fixed by two countersunk screws located underneath, and the drawers that are located need to be removed to be accessible and able to be removed. The simple task of approaching water filtration in such a design requires three steps to complete.
1. Remove the drawer below the water heater.
2, remove the coffee machine, water heater
3, remove the water to approach the panel

The first step is relatively simple, and you can press the shrapnel on both sides of the drawer. The second step is to remove the coffee machine and water heater. The disassembly and assembly of the coffee machine is relatively simple, and the possibility of error is small. The disassembly and assembly of the water heater is also very simple. It is enough to remove the two countersunk screws. But this is an error-prone link. The bottom-up screw itself does not meet the design concept of easy force application in ergonomics, and the working space is narrow. When the fastener is screwed, it is necessary to apply a larger screw along its axis instead of being similar to a hexagon or inside. Hexagonal fasteners. Under the same conditions, the force required to rotate the shaft in the axial direction of the fastener is significantly smaller than that of the screw. All of the above factors are used to loosen the screws when the fasteners are removed.

The narrow working space has again caused a lot of trouble for the remediation of the screwed screws. The conventional methods are not applicable. If the first two steps can successfully carry out the third step, it will be easy.

Let's talk about this one and bring us a series of maddening stories. The story happened during the C-check of the Airbus A321 aircraft last week. When the water heater was to be dismantled, we found that one of the screws was screwed. The scene at the time was similar to the screw in the photo above. That photo was taken yesterday in the same part of another Airbus A321.

In this state, how to handle the screw? The pliers can't be used because it is buried; because of the limited space, ordinary drills can't be used, and air guns can't be used. No way, only the L-shaped drill can be used. Since it is difficult to ensure the verticality from the bottom up, it is easy to drill. In fact, we are really getting worse. At the same time, it is not an easy task to apply a force along the screw axis to the drill bit. Don't you do this, is there any other way? After some twists and turns, the screw head was finally drilled. Without the screw head, the water heater can move up and down. Our goal is to remove the water heater and it needs to be able to move back and forth and take it out. Make sure it moves around. The space above and below the water heater must be large enough to ensure that the remaining screws can pass through the board through which it passes. The actual situation is as shown below.

The space above the water heater is too small for the remaining screws to still pass completely through the board through which it passes. How to do it? Continued drilling will only make the hole bigger and bigger due to the deviation of the drill, and even larger than the nut of the screw, which is obviously unacceptable. If you can't drill, you can only saw it. The space is too small to be sawed by hand with a saw blade. It took half an hour to get it.

Subsequent work is more routine. Apply a new screw and remove the remaining screws from the water heater with a pliers. An original simple job caused so many stories due to design flaws, which cost so much manpower and time.

After observation, it was found that some Airbus A320 aircraft and Airbus A330 aircraft were designed in this way. One of the Airbus A321 aircraft actually found two screws to slip, which is a nightmare for the aircraft. It’s still the power of Boeing. Simple and clear, like one. The picture below shows the water filter location on the Boeing 737-800.

At this point, I suddenly realized that this defect is not only the water filtration process of the drinking water system, but also the design of the fixed method of the hot water machine. The problem arises during the disassembly and assembly process of the water heater. Only the steps of the drinking water filtration removal provided by Airbus (or the kitchen, drinking water system supplier) are unreasonably added to the steps of disassembling the coffee machine and the water heater.

Boeing (the kitchen or drinking water system supplier) is relatively sensible. It is much easier to use the force from the side during the disassembly and assembly of the screw. It is much easier to use the force from below. Even if the screw is slipped due to improper construction, the remediation is relatively easy. . If you want to rate this design, the design of the Boeing 737 is 100, and the Airbus A320 is only 40 points. Boeing's design skills are not blown out.

Of course, this tiny flaw does not prevent the Airbus A320 from becoming one of the most successful aircraft in the world. In many places, Airbus is still worth learning.