The Boeing 737NG overhead has three magnetic switches: Yaw Damper, Wing Anti Ice and the Alternate Flaps. The Alternate Flaps is a three position switch and I’ll skip that. The Yaw Damper and WAI are just two position switches and I’ll concentrate on these. These switches are hard to come by, one can buy used ones but they are expensive. Building them is, once you have the right solenoid, fairly easy.

The simplest way is to find a bi-polar solenoid; this is one where the plunger has two stable positions. By applying a current of the right polarity the plunger can be moved from where it is to the other position. There is one on the market for about € 25, model TDS-K06B 6VDC. Search for it on the internet to find a distributor. The other part you need is a two position tumbler switch. You need a switch where the handle pivots on an axis, not the ones that have a virtual axis. The image on the right clearly shows this.

The first thing you have to do is to remove the switch housing, use a saw to do this and make sure that you don’t touch the underside of the switch handle. Next you have to mount the tumbler handle and solenoid on a piece for metal. You probably have to work on the underside of the switch handle so it slides into the slit of the solenoid plunger. In order to fix the tumbler handle to the solenoid, I made a small cap from aluminum that prevents the handle from slipping out, but still allows some slack for the handle makes a circular movement. Once you have this all working smoothly the last step is to fit a micro switch. I had some lying around and my solution for this is only a suggestion. My design is such that it does not interfere with the surrounding annunciators and switches on the overhead.

A 0/16/16 Phidgets card drives the solenoid directly from a 12V DC supply with a 4.7 Ohm resistor in series.

IIf you have any questions or remarks please send me an e-mail at: pvrijald@planet.nl.

Fully assembled switch