The International Cessna 170 Association

Thank you for the informative posts.

There have been two (2) post citing "safety of flight" issues. Now that I know, I concur.

Apparently there needs to be some "educational" work to inform ALL owner/operators.

Prior owner truly told me just dress warmly and ignore it. So I ask what is instruction from the manufacturer?

An even bigger question now becomes why would competent A/P, IA 's never even mention the frozen cable?
Multiple decades of annual inspections and I and my mechanics have simply ignored a "safety of flight item"

Truly ignorance has no place in the cockpit.

In the thread I created about a new training plane … I pointed out that the cabin air shut-off is a safety-of-flight issue.... as it was the only way to stop the exhaust fumes from entering the cabin on takeoff into weather that made an immediate return problematical.

I believe that many Inspectors overlook this important item on annual inspections and encourage everyone to add it to their preflight actions. Regular exercise of that valve is important and helpful to longevity for BOTH of you.

Am I correct in thinking that the primary reason for the cabin air control is to prevent engine compartment gas from getting into the cockpit when either:

1) You have an engine fire or
2) You suspect a CO leak from a muffler.

Pushing the cabin heat in and pulling the cabin air out should isolate the cabin from engine compartment gases.

I realize this is an important issue. I nearly lost a good friend and his wife to cockpit smoke and fumes though in this case the smoke and fumes where coming from in the cockpit from the firewall blanket that was being cooked by a hot gas jet from a failed muffler in a Super Viking in the engine compartment.

But on the lighter side the other day I was flying my 170 and being about 35° out I kept feeling for that cold jet of air blasting my face. Wasn't coming from the air vent over head. Not from the area of the wing root and windshield. This jet was coming in from the front edge of my door around the (original) seal. If I wanted a cold jet of fresh cool air pointed right at my nose, I couldn't have built it better. I turned to my passenger and without complaint pointed out the fresh air feature my 170 door had.

pdb wrote:

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Am I correct in thinking that the primary reason for the cabin air control is to prevent engine compartment gas from getting into the cockpit when either:

1) You have an engine fire or
2) You suspect a CO leak from a muffler.

Pushing the cabin heat in and pulling the cabin air out should isolate the cabin from engine compartment gases.

You are thinking correctly.

Note that Cessna warns against pulling the cabin air shut-off with cabin heat selected.... Their warning is that the heater muff hoses may be overheated in such a fashion. I would like to point out that those hoses are relatively inexpensive considering the alternative should the pilot not be able to prevent exhaust fumes entering the cabin.
If you cannot shut the cabin heat off and you're getting too warm... Cessna likely presumes you will land the airplane and fix the cabin heat control.
However, if you cannot shut off cabin heat....and you have exhaust entering the cabin (as I did on that Training plane story).... then shutting the cabin air is the only alternative and damn the hoses.

(BTW, the hoses were not harmed at all when I later inspected them. The cabin heat valve was defective which was the reason it would not shut off.... the control cable worked fine.)