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The 737 aircraft use approximately 130 of the Korry Chromalux® 318 and/or 319 indicators in the "Control Cabin" (Boeing's phrase for Cockpit or Flightdeck).

The 318 and 319 indicator assemblies are a Press-to-Test 1/2 by 1-inch indicator, which have three major parts, Cap Assembly, Base Assembly and the Plate Assembly. The Cap Assemblies are indexed so that if they should be removed from the Base Assembly they will only fit back into a Base Assembly that has the same indexing. The Base Assembly, is held in the panel cutout with a "mounting sleeve." The Plate Assembly has the terminal connections, and may have different electrical circuit types depending on the indicator application.

The Cap Assemblies have finger grips on the narrow sides to aid in removing (pulling) the Cap Assembly from the Base Assembly. With the Cap Assembly removed you will have access to Base Assembly. The 318 requires a 5/16" hex wrench to loosen the captive hex stud allowing the Base Assembly to be removed from the Plate Assembly. The 319 only requires a small flat blade screwdriver to loosen the two captive screws attaching the Base Assembly to the Plate Assembly.

The Cap Assembly is made up of five parts, Legend, Light Defuser, Color Filter/Filters, Cap Base and the Incandescent Lamps.

If you look closely at the image above, you will see that the Legend for the 318 has little tabs, the tabs allow the legend to snap into groves in the Cap Base and be held in place. This allows for easy removal of the Legend from the Cap Base. The 319 legend, has no tabs, it is glued to the Cap Base. One note of caution the glue used to attach the Legend to the Cap Base of the 319 indicators, can/will glue the filters to the Cap Base. Be very careful when trying to remove the filter packs from the 319 Cap Base, the filter is only .040" (1mm) thick.

The Light defuser has a frosted side, the frosted side fits into the Legend. Then the colored filter is assembled with the frosted side facing the Incandescent Lamps. The "Amber" color filter is different for the 318 and the 319. In the 318, there is a 040" amber filter, and a flexable .004" red filter that make up the color filter. The 318, uses a .040" amber filter, and a .020" red filter for the color filter. Assembling the filters in this manner matches the majority of Cap Assemblies that I have taken apart. I have asked Korry for the 318 assembly instructions, but as of this writing I have not received any information from them. The one thing I have done is assemble all of then the same way, in hopes that they will have similar appearance when illuminated.

The 318 uses two 28 Volt T-1-3/4 size single contact flanged lamps similar to a number 387 lamp. The 319 uses two 28 Volt T-1-1/4 size single contact flanged lamps similar to a number 737 lamp.

Two types of 318/319 indicators are used, the image on the left is a ground seeking type which requires a ground controlled circuit to turn it on this type is known as a Korry "Circuit Type 1"; The image on the right type is known as a Korry "Circuit Type 2" which is a power seeking type which requires a power controlled circuit to turn it on. The majority of the 318/319 indicators used in the 737 are the ground seeking "Circuit Type 1".

Pressing the Cap Assembly operates the momentary switch which causes the light to illuminate (push-to-test). There is also a connection for "Master Test" which is used to illuminate the indicator lamps. Both types of indicators circuit 1 and 2 use isolation diodes to prevent interaction between the master test and the circuitry driving the indicator.

The 737NG also use a third type of Korry 318 indicator this part number is 318-630-1012-002. This part number has a legend that reads "BELOW G/S" "P-INHIBIT" with an "AMBER" color when illuminated. This special indicator has a dry set of momentary contacts which are controlled by pressing the Cap Assembly.