Home > Filtered Air Box, Firewall Forward > Installing Alternate Air Control Cable – 2.5 hrs

Installing Alternate Air Control Cable – 2.5 hrs

Tuesday May 7, 2013

I started out to install the control cable for the alternate air door on the FAB. The obvious question was how to route the cable and where to mount the knob. I don’t really want this control to be accessible to the right seat passenger because the cowl has to be removed to reset the door if the knob is pulled. If the alternate air door needs to be opened, the pilot should be the one to do it. So I decided to put the knob under the subpanel on the left. It can be easily reached by the pilot but is not anywhere close to the cabin heat knob which looks almost identical.

The cable routing is trickier. I could not find any information on the forums for my configuration so I had to figure this out myself. After considerable head scratching I decided to route it through the firewall recess directly above my mixture cable. Then the cable turns downward along side the mixture cable and then turns forward to the bottom of the air box. Once I settled on that I became concerned that it might interfere with the VPX-Pro control box so I had to temporarily mount that to check for interference. The photo below shows the VPX on two .063 angles approximately 19-5/8 long. This is just held to the ribs by cleco clamps right now but it gave me enough confidence to proceed with the cable installation.


I made a small bracket out of .040 aluminum to mount the knob to the left bulkhead just beneath the cool air vent scat tube. Then I punched a hole in the firewall recess directly above the location where the mixture cable feedthru was placed. Installed there an eyeball feedthru with a .188 diameter hole which fits the alternate air cable perfectly. In this photo you can see how the cable routes in an S bend above the rudder pedals.


Here is a view from above after I added a couple of zip ties to hold the cable down below where the VP-X will mount. The bends are gentle and the cable knob moves freely. This routing is good with the stock 6 foot long cable.


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