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Water in Pitot Line

avrojockey

Well Known Member
Patron
So...

Flying in a bit of moister of the past couple trips. One trip rained the entire flight, well above freezing, and the other was just light snow for a small portion of the flight.

After sitting outside for a couple days, well below freezing for the first time this winter, I had a blocked pitot line and/or tube. No IAS, during subsequent flight.

Not sure how the pitot line got blocked with water but it did. After sitting in my hanger 40+F for a few hours, I disconnected the line on both sides and blew it out.

I have a heated GAP26 (unregulated). The GAP 26 has internal baffling and drains for moisture protection.

Any thoughts on why this would happen?
 
Wild guess- possibly condensation over a long period of time eventually produced a puddle of water? Maybe the humid air during the rain day flight just tipped the condensation formation.

Wild guess #2- I wonder if it would be advantageous to leave the 2 tubes coming out the top of the GAP26 vertically straight & making the bend as close to the top wing skin as possible, in essence create an air trap similar to what is done with a fuel tank vent line.

Have never ran into that situation & fingers crossed, hope I never do.
 
I think a droplet or two (or condensate) got trapped in the baffling and froze at at altitude. I doesn't take much to block the pitot line. I had a similar situation years ago over Nantucket island in February. Airspeed fluctuates at first then within minutes creeps to zero. Stock Vans tube no preheat. Disconcerting for sure but nothing dangerous in clear VFR within airport boundary.
 

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Probably a good idea to flip on PH anytime flying in rain/snow/visible moisture, helps to keep the probe clear of moisture.

Also think it’s a good idea keeping the lines up high to keep water from migrating into the line, basically the same way we do for the static system.
 
Definitely using PH now in any visible moisture. What may have contributed was me turning off pitot heat right after landing...could've left it on to burn off any residual.

Loss of airspeed indication was remarkably uneventful (VFR). Though my AOA wasn't working either which required some pilot math...

A quick HW component calculation (110 minus degrees off runway heading is roughly the percentage of HW component) and simply flew groundspeed adjusted. I knew the mental math book would come in handy some day.
 
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