Steve,

 

I have raised this issue before - Generally, all fast non-pressurized aircraft have lower than ambient pressure in the cabin.  Generally, the cowl outside the cooling plenum has a pressure slightly higher than ambient.  Any opening in the firewall allows cowl atmosphere to enter the cabin.  Make sure any firewall pass-throughs are sealed as best as they can be.  Remember that burned-through cowl-located heater SCAT hose will also allow fire products to enter the cabin.

 

A side note:  The drain hole in the belly under the center console drew exhaust into the cockpit.  I found this when I installed a digital CO monitor.  The hole is now plugged.

 

Scott Krueger AKA Grayhawk     

 

 

Years ago Van’s tested several factory built RV’s for smoke penetration of the firewall.  I remember they were amazed how much smoke they got thru what they thought were pretty tight electrical, cable and misc. fittings in a ground simulation.  They tightened up the obvious holes and used High Temp Silicone and still had an unacceptable volume of smoke coming in. 

 

Fire or even an oil leak might have smoke that could prevent breathing long enough or obscure vision or be enough of a distraction (pick one or more) to set up a fatal scenario.  This could have been a factor in the Watsonville crash.

 

Steve Colwell  Legacy