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Boeing 747-400 CRT switch panel
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introduction
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This is an article about the switch panel of an Boeing 747-400 aircraft. This panel switches the crt (Cathode Ray Tube) display information. This panel is located on the left side of the main instrument panel (MIP). This panel is operated by the captain of the aircraft. Mainly I'm interested in Airbus panels so this is a nice sidestep for comparison. This panel is also known as assemby with part number: 233U2201-3.
 | Since my main interest is for Airbus equipment, this panel is for sale. Please contact me if you're interested in purchasing. This panel is available for €150. By the way; there are several other Boeing panels available for purchase as shown below. |
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original use
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 This panel is located at the left hand side of the cockpit main instrument panel. The location is marked on the image shown here. The panel is used in the following aircrafts:
 747-400
747-400EF
747-400F
747-400PC
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controls
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 The exact operation of this panel is unkown since I'm not a pilot... Based on the markings this panel is used for routing the display information. Back in the days the displays were cathode ray tubes (CRT's) so the display indications are abbreviated to 'CRT' on the panel. Usually the primary flight display (PFD) and the navigation display (ND) are the main displays used in front of te pilot. The two 'stacked' displays in the middle are for technical and other information like the engine information, warning messages and for example fuel information. If the primary flight display (PFD) or the navigation display (ND) fail, the pilot misses information. Therefore the information can be routed to the 'stacked' displays in the middle. In normal operation, both switches are in the middle 'normal' position. By rotating the left knob, the upper display can be switched to display the Engine Indicating and Crew Alerting System (EICAS) or the Primary Flight Display (PFD). The right knob is used to display the Engine Indicating and Crew Alerting System (EICAS) of navigation Display (ND) information on the lower display. So in normal operation these knobs are probably never used unless there's a technical malfunction and this is a nice back-up feature.
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reverse engineering
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 The panel is rather straight forward. It's just point to point wiring. The wire loom is therefore rather simple. There are two switches marked [S1] and [S2] with part number AC45-0009-2. There's a ground/chassis connection [E1] and a connection for the panel illumination [J2]. There's a 12-pin circular connector marked [P2] for connecting to the aircraft's electrical system. The reverse engineering is done by following the wires and resistance measuring between the pins and the other end of the wire.
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schematic
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The schematic is shown below. It's just the reverse engineering drawing, but this should be good enough to use. So aircraft simulator builders can use this information probably... The schematic is rather self explanatory I guess...
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backlight test
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 The panel illumination is powered with (the default) 5 VAC for illumination. I tested the illumination with 5 VDC and the current is measured 251 mA. That results in a power consumption of almost 1,3 Watts.
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Boeing/Airbus panel comparison
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I compared the engineering of Boeing and Airbus panels. Both panels are good for the job. But my verdict is that Airbus panels a much more sophisticated and thought trough. The Airbus panels have always redundant ground wiring where Boeing panels have 'just' one wire. For Airbus panels is each component clearly marked with the identification tag. Even the wire assembly and ground bond are marked. For Boeing are the components marked with a pen and the identification is sometimes confusing. For example, on this panel are three part numbers mentioned: 233U2201-3, 233U2211-3 and 233U2211-4. And it's hard to find out which number is a part, sub assembly or main assembly.
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