Coincidence? Not likely...

Gilbert Buettner

Gilbert Buettner

Cleared for Takeoff
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Dec 5, 2022
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Wausau, Wisconsin
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Gil
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KAUW
Within the past week, three of our five airplanes have had airspeed indicator failures. Two on one day. These are trainers that fly very often, and unfortunately were flown quite a bit during the period of smoke from the Canadian wild fires.

Speculation is small bits of ash caused the failures. And that, my friends, is what we were breathing.
 
Oof. Not good.
I had something like three sessions cancelled since the smoke caused less-than-VFR visibility minimums.
 
Gilbert Buettner said:
Within the past week, three of our five airplanes have had airspeed indicator failures. Two on one day. These are trainers that fly very often, and unfortunately were flown quite a bit during the period of smoke from the Canadian wild fires.

Speculation is small bits of ash caused the failures. And that, my friends, is what we were breathing.
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I saw a FB post by a John Chmiel about these failures as well. I have to be honest I had been wondering if there would be any issue flying in that smoke. It obviously was thick enough to irritate a person's sinuses and lungs, and you could clearly smell the smoke. We all know to avoid ash clouds from volcanos due to the ingestion hazard, where is the particulate threshold between safe or potential damage?
 
Had an altimeter freeze up at work recently. Maybe not smoke related but the first time I’ve ever seen that happen. First time I’ve turned down a flight at night (3-4 miles) due to visibility from smoke as well.
 
Why would an ASI fail because of smoke? Air doesn't pass through the airspeed indicator or the altimeter. They both measure pressure at a point (or points) located 10' or more away from the instrument and only connected to the instrument through small tubing.
 
kyleb said:
Why would an ASI fail because of smoke? Air doesn't pass through the airspeed indicator or the altimeter. They both measure pressure at a point (or points) located 10' or more away from the instrument and only connected to the instrument through small tubing.
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The smoke contains ash particles which apparently blocked the pitot tubes.
 
Gilbert Buettner said:
The smoke contains ash particles which apparently blocked the pitot tubes.
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Extremely doubtful, but I'll play.

If that's the case, how'd those ash particles entering a pitot tube 10' or more from the instrument actually reach the instrument to fail it? Remember, there is no flow in the airspeed indicator system.
 
You sure you don't have a new rental pilot/instructor/student that is blowing on the pitot tube during preflights to test things? Maybe a new line guy washing the airplanes that is getting a little carried away with his compressed air?

Could be the smoke...but in a flight school environment...never under-estimate the humans...
 
jesse said:
You sure you don't have a new rental pilot/instructor/student that is blowing on the pitot tube during preflights to test things? Maybe a new line guy washing the airplanes that is getting a little carried away with his compressed air?

Could be the smoke...but in a flight school environment...never under-estimate the humans...
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Three airplanes in a few days. Different students and instructors. I dunno, just what the A&P thinks.
 
Baked Potato said:
Oof. Not good.
I had something like three sessions cancelled since the smoke caused less-than-VFR visibility minimums.
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I have had most of August and September flying (instruction) due Less than VFR minimums.

Wasn't to bad for my few instrument students, other than breathing it, but that was pretty much the same on the ground as it was in the air.

Brian
CFIIG/ASEL
 
As one of my mechanics wrote in my logbook: doobers.
 
Gilbert Buettner said:
The smoke contains ash particles which apparently blocked the pitot tubes.
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I find that hard to believe, as the smoke particles in question are less than 2.5 micrometers in diameter, and air doesn't flow through the ASI system. More likely something larger, like bug detritus. Insect collisions will be more frequent at lower altitudes typical of pattern work and landing practice.
 
Let'sgoflying! said:
If only those Canadians would put out the darned fires, c’mon!
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The fires affecting the northeast are located in extreme northern Ontario and Quebec, which are incredibly isolated and remote. No one is getting in there to do any firefighting. They are likely going to burn until snowfall. Enjoy.
 
chemgeek said:
I find that hard to believe, as the smoke particles in question are less than 2.5 micrometers in diameter, and air doesn't flow through the ASI system. More likely something larger, like bug detritus. Insect collisions will be more frequent at lower altitudes typical of pattern work and landing practice.
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That is the point. The air does not flow though the system, so the particles enter the open end of the pitot, lose energy and are deposited. Nothing to flush them out.
 
Pinecone said:
That is the point. The air does not flow though the system, so the particles enter the open end of the pitot, lose energy and are deposited. Nothing to flush them out.
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The particles (PM 2.5) in question are too small to "deposit" by gravity. PM10 will settle a little quicker, but only in quiescent conditions, with a half-life of hours. To collect these particles you have to pump them through a special filter for quite a long while to collect enough to measure. At its worst, we are talking about something like 40 micrograms per cubic meter of air in smoky regions. A pitot tube cannot collect any significant volume of air. But if the whole pitot system were filled with smoke and all the particles magically settled (they won't) you could only collect sub-microgram quantities of solid material, not nearly enough to clog a pitot tube. The indicator is pretty far upstream and it is hard to imagine deposition of any significant quantity of PM2.5 or PM10 that far upstream of the entry point.
 
The are impacted by their velocity. Like a centrifugal collector.
 
Pinecone said:
The are impacted by their velocity. Like a centrifugal collector.
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Inertial impact collectors for small particulates require high net flow rates for efficient particle collection. There is no net flow rate through the pitot system. The quantity of PM2.5 particles that could collect in a pitot nozzle is going to be negligible.
 
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