HNLsurfer
Topic Author
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Freezing Pitot Tubes

Tue Oct 25, 2011 1:23 am

Why don't they manufacture them with a tiny coil heater to prevent freezing? Or do I not know what I am talking about?
 
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longhauler
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 1:25 am

Quoting HNLsurfer (Thread starter):
Why don't they manufacture them with a tiny coil heater to prevent freezing? Or do I not know what I am talking about?

If you don't know the answer, then the question is worth asking.

And yes, pilot tubes are heated.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
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longhauler
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 1:26 am

Quoting longhauler (Reply 1):
And yes, pilot tubes are heated.

Good heavens, that almost sounds naughty!
Of course, I meant pitot tubes.  
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
HNLsurfer
Topic Author
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 1:27 am

Quoting longhauler (Reply 1):

Then are the heaters failing? Or are they not hot enough?
 
NWAROOSTER
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 1:39 am

Quoting HNLsurfer (Reply 3):
Then are the heaters failing? Or are they not hot enough?

The heaters do fail, which can cause them to freeze up. The Pitot Heat is supposed to be checked on the ground on a regular basis. It is also possible for the heaters to loose power due to a faulty circuit breaker or not being turned on.
A light should be illuminated on the overhead panel if the Pitot Heat is not on.   
Procrastination Is The Theft Of Time.......
 
CX Flyboy
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 2:03 am

It should also be noted that in the most severe of thunderclouds, it is possible that ice accretion is faster than the ability of the heated tubes to melt the ice. This can cause problems obviously although normally aircraft that have experienced blockages due to ice have had the blockages clear within a couple of minutes as by then the aircraft is normally out of the cloud causing the problems so the ice has stopped accumulating and the heat does its job to melt the remaining ice. This was also the cause in AF447 where the blockage itself did not last long and once cleared the aircraft became totally serviceable once again.
 
Type-Rated
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 5:42 am

Even small aircraft have pitot heat. I have seen it even on a Cessna 150 before.
Fly North Central Airlines..The route of the Northliners!
 
AA737-823
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 6:09 am

Quoting HNLsurfer (Reply 3):
Then are the heaters failing? Or are they not hot enough?

Well, for the most part, they aren't. Pitot tubes haven't appreciably changed design in many decades.
There's only one model of airliner that seems to have trouble, and even then, it seems to be predominant with one pitot probe manufacturer, rather than the other. Which is why the Directive stated that the probes should be changed to the other brand, as I recall.

Unfortunately for AF447, incorrect pilot response also played a starring role in the tragedy. But, in my humble opinion, the guys didn't really stand a chance- they were given insufficient information from which to make good decisions.

So, to your original question, there isn't typically a problem with pitot probe heat.
 
FlyHossD
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 7:46 am

Pitot heat can also be too strong and trip the circuit breaker. Years ago, one of the aircraft I often flew did just that and within a few minutes, the pitot tube would ice up, leaving me without any airspeed indication to fly by. Despite numerous "write-ups" the operator never fixed it and I came to be quite good at flying with no indicated airspeed.
My statements do not represent my former employer or my current employer and are my opinions only.
 
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Starlionblue
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 8:46 am

Quoting flyhossd (Reply 8):
Pitot heat can also be too strong and trip the circuit breaker. Years ago, one of the aircraft I often flew did just that and within a few minutes, the pitot tube would ice up, leaving me without any airspeed indication to fly by. Despite numerous "write-ups" the operator never fixed it and I came to be quite good at flying with no indicated airspeed.


And you are still among us. So it is possible to fly with no airspeed indication.

 duck 

[Edited 2011-10-25 01:47:01]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 9:52 am

The Heater element in the coil keeps the area around the probe from not freezing.
Common mistake in Maintenance......remove the Pitot covers before running the engines or putting the aircraft in to air mode during Maintenance [On most types]
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flipdewaf
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 9:53 am

Quoting Starlionblue (Reply 9):
So it is possible to fly with no airspeed indication.

Only if you have back driven throttles!

  

Fred
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Fabo
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 11:11 am

Quoting flipdewaf (Reply 11):
Only if you have back driven throttles!

Or no throttles   We were taught to fly without airspeed indicators in gliders, although I suspect icing was not the predominant factor in airspeed indication failure in Blaniks. Mechanical blockage sounds more likely to me in that.
The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
 
SAAFNAV
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 3:36 pm

Quoting Starlionblue (Reply 9):

And you are still among us. So it is possible to fly with no airspeed indication.

Familiar Power with Familiar Attitude will save your behind.
Recognizing that you have to do that in midst of a crisis, that might be something else.

I also do gliding, and we do Blank Panel training. It's quite easy, as you have no engine to drown out the wind noise..

Erich
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RaginMav
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 5:11 pm

Quoting HNLsurfer (Reply 3):
Then are the heaters failing?
Quoting AA737-823 (Reply 7):
So, to your original question, there isn't typically a problem with pitot probe heat.

Furthermore, airliners have three independent heated pitot tubes. Should one fail, the other two should continue to operate normally.

By extention, the most likely way to have no valid airspeed indication is to have all pitot sources freeze up, as can happen in severe icing conditions.
 
FlyHossD
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 9:07 pm

Quoting Starlionblue (Reply 9):
And you are still among us. So it is possible to fly with no airspeed indication.

The first time it happened, I was in a descent in icing conditions near CLE. At first, I saw a decrease in airspeed and so I lowered the nose to increase speed. However, the speed continued to decrease and then I thought to check the VSI (I had also noticed that the wind noise was louder than normal). Seeing the the vertical speed was great - and that the airspeed was still decreasing - I now knew the airspeed indication was incorrect.

After landing, I found the circuit breaker to be popped and then reset it.

On the return flight, I heard the circuit breaker pop and flew again without a reliable airspeed indication. Unfortunately, our mechanics were never able to repeat the failure on the ground and so the aircraft was released time and time again.

So yes, pitch and power became (unfortunately) common for me. And yes, I wonder what the crew of AF447 saw and what they believed to be happening (I have no Airbus experience to draw from).
My statements do not represent my former employer or my current employer and are my opinions only.
 
cmf
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 9:30 pm

Quoting flyhossd (Reply 15):
After landing, I found the circuit breaker to be popped and then reset it.

One circuit for all pitots?
Don’t repeat earlier generations mistakes. Learn history for a better future.
 
KELPkid
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 11:53 pm

Quoting Starlionblue (Reply 9):
And you are still among us. So it is possible to fly with no airspeed indication.


Definitely not the most ideal of situations, especially when flying in IMC or night (with no visible horizon). You can be trained to do anything. When I was getting my instrument rating, one would think that the vacuum system was most unreliable, and I would have to fly entire flights partial panel (in most GA planes, the attitude indicator and the DG are vacuum-powered). You can thank your flight instructor with the little rubber instrument covers for that   Throw in a hold at an NDB while partial panel (in a plane with nothing but a simple ADF indicator), and cockpit workload goes sky high. To top it off, you are being trained to do it alone at the Private Pilot level, no crew members to sluff the work off onto   

I vaguely remember my instructor covering the airspeed indicator a time or two, he usually gave it back to me when I went through the checklists and turned on the pitot heat   One time he had me land without it (at the end of a simulated ILS to minimums...). As long as you have a working attitude indicator, everything seems to be okay. In most GA planes, the stall warning system is independent of the pitot system, so you'd at least have warning if you were getting too slow (as long as the stall horn or stall warning tab doesn't get iced!    ). You can also use rate of descent/climb and general knowledge of power settings during the various phases of flight to your advantage to keep the airspeed under control... I would take 10 airspeed failures to one actual instance of a vacuum system failure any day and twice on Sundays.
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FlyHossD
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RE: Freezing Pitot Tubes

Tue Oct 25, 2011 11:56 pm

Quoting cmf (Reply 16):
One circuit for all pitots?

In this case, yes. IIRC, all transports are required to have separate systems to maintain the redundancy of the systems. My story was about a Piper Seneca that I flew (freight) in my first flying job - about 30 years ago (feels like 80). That airplane had only one pitot system.
My statements do not represent my former employer or my current employer and are my opinions only.
 
N49WA
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RE: Freezing Pitot Tubes

Sun Nov 13, 2011 1:21 am

Not too long ago I was at KHHR to greet our Lear when it landed after a job. Right after engine shutdown I put my hand on the pitot tube (no particular reason, just not thinking about it). The burn blisters took a couple of weeks to heal. Lesson learned.
If it's new and quiet, I don't want to fly it.
 
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HAWK21M
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RE: Freezing Pitot Tubes

Sun Nov 13, 2011 12:53 pm

Quoting N49WA (Reply 19):
Lesson learned.

Its a Caution in our Basic training.....Even checking is done by tapping lightly to sense heat before covers can be put on.
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rfields5421
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RE: Freezing Pitot Tubes

Mon Nov 14, 2011 2:30 pm

Quoting AA737-823 (Reply 7):
There's only one model of airliner that seems to have trouble, and even then, it seems to be predominant with one pitot probe manufacturer, rather than the other.

Really - I never thought the Boeing 777 was a problem model.  

The Thales probe involved in the AF447 crash was deemed to have a very slightly higher than normal failure rate. Those failures occured with greater frequency on the A320 family of aircraft than on the long range aircraft. It was due to the type of flying the aircraft do - the higher number of climbs and descents through known icing that the long range aircraft.

That is why the priority on replacing that model probe on the A320 and B737 sized aircraft than the long range aircraft like the A330/ A340 aircraft, though at Air France - that replacement process had begun when AF447 disappeared.

Yes, Airbus tends to use Thales probes more than Goodrich probes. Thales is part of the general European aircraft industry which supports Airbus. But Thales is a huge company - they even have at least three facilities here in Dallas (They have the old Raytheon plants/ business).

And yet - B777 aircraft with the 'good' Goodrich probes have been documented to fail/ freeze in flight on occasion.
 
ThirtyEcho
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RE: Freezing Pitot Tubes

Wed Nov 16, 2011 2:20 am

As mu first instrument instructor asked, after I suffered an airspeed indicator failure under the hood, "You can't fly an airplane without an airspeed indicator?" Silly me, duh, of course I could.
 
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ADent
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RE: Freezing Pitot Tubes

Wed Nov 16, 2011 7:37 pm

The AF447 pitot tubes were only iced over for a short time - under 1 minute. The incorrect speed was displayed for 29 seconds on the left PFD and 54 sec on the ISIS.
 
KELPkid
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RE: Freezing Pitot Tubes

Wed Nov 16, 2011 9:14 pm

Quoting ADent (Reply 23):
The AF447 pitot tubes were only iced over for a short time - under 1 minute. The incorrect speed was displayed for 29 seconds on the left PFD and 54 sec on the ISIS.

Still, the worst time for an airspeed indicator to fail is at cruise, at night, in IMC (or even over the ocean with no visual reference whatsoever!). If you react before trying to diagnose, you might find yourself dead   As I recall, the aircraft was in a climb when the first stall warning occurred...

On climbout or approach, you might actually be expecting an airspeed indicator, especially if you know you are descending through or climbing through icing. Blundering through the outer bands of a tropical thunderstorm during cruise with large supercooled droplets (enough to ice up the already heated pitot tubes) is probably the exception rather than the norm.
Celebrating the birth of KELPkidJR on August 5, 2009 :-)

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