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Pitot tube temperature

Posted: Sun Apr 11, 2021 2:29 pm
by AvgWhiteGuy
Does anyone know a ballpark temperature that pitot tubes are heated to on commercial airliners? GA?
Thank you.

Re: Pitot tube temperature

Posted: Sun Apr 11, 2021 2:46 pm
by GalaxyFlyer
No, but if on—don’t touch them. They’re pretty hot, will melt covers.

Re: Pitot tube temperature

Posted: Sun Apr 11, 2021 5:07 pm
by fr8mech
For whatever reason, I didn’t read through the whole thing...just looked at the pictures, our B767 AMM has a color picture of a thermal image of a pitot/static probe in operation.

The image showed a max temp of 550.8F, a min temp of 119.2F with an average temp of 238.6F. I do not know the time interval, nor the air/ground state of the aircraft. It appears the imager was targeted on the tip.

Re: Pitot tube temperature

Posted: Sun Apr 11, 2021 5:24 pm
by Phosphorus
Soviet certification requirements (cold in winter, too many insects in the summer) basically had pitot tubes heated to the point of rainbow colours on the surface (температура побежалости).
So no matter how cold, pitot heating "on" means no ice blockage. And no matter how hot, all insects are burned away, and no organic matter blockage.

It had consequences -- static air generally did not provide enough cooling, even in cold weather. So pitot tubes heating had to be either turned on by an event, signifying rotation (like landing gear no longer supporting the weight of the plane), or manually by the crew. Otherwise, the tubes risked overheating.

Re: Pitot tube temperature

Posted: Sun Apr 11, 2021 6:58 pm
by fr8mech
Phosphorus wrote:
And no matter how hot, all insects are burned away, and no organic matter blockage.


We’ve pulled plenty of charred insect carcasses from the tubes if the covers were left off in the spring/summer. Damn bugs only need a few minutes after the probes cool down to get in there and do their thing.

Of course, the probe has to be replaced, but we’d try to capture any organic material and send it off...somewhere...for classification purposes. I wonder if we’re still doing that.

Re: Pitot tube temperature

Posted: Mon Apr 12, 2021 4:26 am
by Max Q
One of many good features on the 757/67 was automation of pitot heat operation

No switches exist to turn them on and off, they come on automatically after engine start


More than a few accidents and incidents over the years due to iced up pitot tubes after pilots forgot to turn them on


This was a good idea

Re: Pitot tube temperature

Posted: Mon Apr 12, 2021 11:13 am
by Phosphorus
fr8mech wrote:
Phosphorus wrote:
And no matter how hot, all insects are burned away, and no organic matter blockage.


We’ve pulled plenty of charred insect carcasses from the tubes if the covers were left off in the spring/summer. Damn bugs only need a few minutes after the probes cool down to get in there and do their thing.

Of course, the probe has to be replaced, but we’d try to capture any organic material and send it off...somewhere...for classification purposes. I wonder if we’re still doing that.



I don't believe Soviets eventually bothered with that, past certification flights. In places like Yakutia, basically you have several (like 3-4) months a year, when it's not freezing, and that's when all life (insect life included, of course) has to go through its annual cycle, before it has to hibernate for the rest of the year. Gnat and other insects are literally swarming, and are attracted to ANYTHING that's not static air. So windshields of planes are covered in organic matter following a roll, and of course pitot tubes are full of that as well, before it burns off.

Max Q wrote:
One of many good features on the 757/67 was automation of pitot heat operation

No switches exist to turn them on and off, they come on automatically after engine start


More than a few accidents and incidents over the years due to iced up pitot tubes after pilots forgot to turn them on


This was a good idea


Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.

If you design a plane that has to do milk runs between places like that, for a living, you start to yearn for simplicity. Otherwise, pilots might have it easier, as long as everything works. As soon as something breaks down, a mechanic has to go out there (not necessarily having a benefit of a hangar) and actually fix stuff. With -40oC (sometimes -70cC, actually) in winter, and insect swarms in summer.

Re: Pitot tube temperature

Posted: Mon Apr 12, 2021 2:01 pm
by fr8mech
Phosphorus wrote:

Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.


Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.

Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.

Re: Pitot tube temperature

Posted: Mon Apr 12, 2021 7:53 pm
by Phosphorus
fr8mech wrote:
Phosphorus wrote:

Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.


Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.

Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.


In Soviet Russia, the switch relays YOU! (/sarcasm)

Soviet designs, where pitot tube heating was activated automatically, relied on landing gear instrumentation. Once load on the landing gear fell, it was assumed the plane was airborne, and pitot tube heating kicked in earnest. Manual switch allowed to ditch the whole thing, and simplify landing gear design.

Re: Pitot tube temperature

Posted: Tue Apr 13, 2021 2:22 am
by Starlionblue
Phosphorus wrote:
fr8mech wrote:
Phosphorus wrote:

Adding automatic pitot tube heating activation adds an additional point of failure. Nice when you a have a "mainline airliner", visiting these "hellholes" rarely, only to get back to the safety of well-stocked base in a more pleasant locale after a quick turn.


Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.

Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.


In Soviet Russia, the switch relays YOU! (/sarcasm)

Soviet designs, where pitot tube heating was activated automatically, relied on landing gear instrumentation. Once load on the landing gear fell, it was assumed the plane was airborne, and pitot tube heating kicked in earnest. Manual switch allowed to ditch the whole thing, and simplify landing gear design.


Don't you need the gear sensing anyway for other things, e.g. gear downlock on the ground and spoiler extension. (Granted, those aren't strictly necessary but they're very nice to have.) Did they really remove the gear sensor just to simplify probe heat?

Re: Pitot tube temperature

Posted: Tue Apr 13, 2021 6:30 pm
by Phosphorus
Starlionblue wrote:
Phosphorus wrote:
fr8mech wrote:

Does it really? You’ve removed the manual switch, which is prone to both electrical and mechanical failure and replaced it, on the B757/B767, with a relay. Yes, the relay can fail, but on those 2 types, the Engine-Out relays are used through out the aircraft, so they should generally be available in station stock.

Further, even though most guys go for the relay, it really is a low probability fix for that particular issue. The current sense relay is where I would go for a first-try quick fix, but the probe is the most likely culprit. Again, that’s 30+ years experience on type and not through any analysis I’ve done. Though, the last 10 or so years, I’ve been in our Tech Support department, and see all the “replaced relay, no help” or the “replaced relay, ops good”, only to have the problem return at the next station.


In Soviet Russia, the switch relays YOU! (/sarcasm)

Soviet designs, where pitot tube heating was activated automatically, relied on landing gear instrumentation. Once load on the landing gear fell, it was assumed the plane was airborne, and pitot tube heating kicked in earnest. Manual switch allowed to ditch the whole thing, and simplify landing gear design.


Don't you need the gear sensing anyway for other things, e.g. gear downlock on the ground and spoiler extension. (Granted, those aren't strictly necessary but they're very nice to have.) Did they really remove the gear sensor just to simplify probe heat?


Good question. Someone more knowledgeable should chime in. But knowing Soviet engineering logic, I would guess these would be separate sensors in separate locations.