I am told by my maintenance engineer that NOTHING is to be put on the dashboard area above the instrument panel - this is where I keep my DUAL GPS to have an unobstructed view of the sky. It was asserted that it could block one of the vacuum vents that are on the top of the dash.

I follow rules to the 'T' but similarly to make up rules 'on the go' is also not appropriate - I could not find a single word about this in the POH?

Can someone tell me if it's allowed and/or safe to place objects there?

  • $\begingroup$ What is the question? Our club has the same policy, and it's not in the POH... I've rented PA28's, the school had the same policy, not just for that aircraft, but all of them. $\endgroup$
    – Ron Beyer
    Commented Jun 11, 2018 at 12:54
  • 1
    $\begingroup$ I learned not to put things on the glareshield because it could scratch or wear the windscreen plexiglass. Nothing in the POH, but that doesn’t mean it’s allowed... $\endgroup$ Commented Jun 11, 2018 at 14:04
  • $\begingroup$ Thanks for the comments - the question is, why should you not put a DUAL GPS unit on the coaming panel - are there any technical reasons or is it just to prevent something from scratchin the windscreen , which I fully accept and understand. $\endgroup$
    – Neels
    Commented Jun 11, 2018 at 21:37

1 Answer 1


Next time you go flying just stick your hand up there and see if you can feel any suction at those holes when the engine is running. I doubt it. The holes in the coaming panel (the flat panel on top of the dash) near the base of the windshield are defroster outlets.

The vacuum pump on the engine accessory case sucks air through the air driven gyros on the instrument panel through rubber hoses interconnected to the vacuum instruments (on the Cherokee there is a regulating valve/manifold between the pump and the instruments). On the upstream side of the instruments there is an intake hose with a cylindrical filter to filter the cabin air before the pump pulls it through the gyros.

The filter is mounted in the open below the instrument panel somewhere in the jungle of wires and tubes, on a bracket of some kind. If you slide on your back and get your head under the panel, you should be able to spot a cylinder about the size of a small can of beans with a wire mesh around it and pleats like a car air filter. That's the vacuum system filter.

The main thing to be wary about when putting electronic devices on top the panel is they may or may not alter the wet compass when turned on. Better to have an external antenna you can stick there and keep the GPS unit on a control wheel clip or something like that.


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