WoW system
 

I am looking into how the undercarriage WoW system functions when based on proximity switches and not contact switches and i'm struggling to find any content online, wondering if any of you guys could shed some light,

Thanks!

You didn't look very hard....

This should help.

https://www.faa.gov/regulations_poli...a/ama_Ch13.pdf

Functional Description - Nose Sensing
The nose air safety sensor sends target position signals to the nose air sensing proximity switch card. The proximity switch card operates nose ground sense relays.
This is the sequence for the nose air sensing when the airplane is on the ground:
- Target moves far from the nose air safety sensor - Nose air sensing proximity switch card sends
electrical ground to nose ground sense relays - Nose ground sense relays energize.
The opposite of the above happens when the airplane is in the air. The nose sensing in air red light comes on when the nose air sensing is in the air mode.

Functional Description - Air Sensing
The air safety sensor sends target position signals to the air sensing proximity switch card. The proximity switch card operates air sense relays.

- Target moves far from the air safety sensor
- Air sensing proximity switch card sends electrical
ground to air sense relays
- Air sense relays energize
- Air sensing in air red comes on.
The opposite of the above happens when the airplane is on the ground.

Functional Description - Ground Sensing

The ground safety sensor sends target position signals to the ground sensing proximity switch card. The proximity switch card operates ground sense relays.
This is the sequence for the ground sensing when the airplane is on the ground:
- Target moves near the ground safety sensor - Ground sensing proximity switch card sends
electrical ground to ground sense relays - Ground sense relays energize.

The opposite of the above happens when the airplane is in the air. The ground sensing in air red light comes on when the ground sensing is in the air mode.

737 has prox switches on its gear

Hello Frostywing. I'm very familiar with the Bombardier Global undercarriage. This uses a plethora of proximity switches to monitor door, leg and oleo extension. Each proximity switch had a steel 'target' that was sensed when in close proximity to the sensor. In effect it was like a microswitch but didn't need to physically move the switch. The target had to be very close to the proximity sensor - probably no more than 3-8mm for it to be sensed.

Of all the undercarriage malfunctions I was aware of (10 or so) all but one was caused by the steel target falling off. This meant, say, when the nose doors did close, the sensor couldn't see the target and so wrongly reported the doors as still being open!