pitot heat question

Coming back from Mammoth this past Sunday and flying through a snow
cloud West of the Sierras, I had the Pitot freeze over. I realized it
was frozen when I tried to correct for altitude gained in turbulence
and the airspeed indication didn't increase even as I pushed the nose
down and could hear the relative wind increase. Not a big problem -- I
could see where I was going on the AI, and a minute or less after I
turned Pitot heat on, ASI returned to normal.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Ari.

--
Elections only count as free and trials as fair if you can lose money
betting on the outcome.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike

I would think that leaving the pitot heat on all the time would be
unecessary wear and tear.
Turn it on before entering visible moisture.. or as soon as you can. Turn it
off when not
needed.

"K. Ari Krupnikov" wrote in message
...

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Only that having it on when you have no airspeed may overheat it and cause
unnecessary wear and tear. I put it on as part of the line-up checks and
switch it off as part of the after-landing checks.

I think most airlines do the same -- just because the big boys do it doesn't
mean we should automatically follow suit, but in this case, as you found, I
figure that prevention is better than cure. Weren't some of the Piper
Malibu accidents attributed to loss of control after the pilot forgot the
pitot heat?

Finally, the pitot heat can make a difference to the compass. At least in
my part of the world, the compass is swung with the pitot heat on.

Julian Scarfe

Leave it on all the time. Every checklist for a turbine airplane that I
have seen says to turn it on. All airlines leave it on all the time. Since
the heat is just a resistance element with no moving parts, I doubt that it
will "wear out faster" as others have suggested. Mine have 4600hrs on them
and presumably they have been on all that time.

Mike
MU-2


"K. Ari Krupnikov" wrote in message
...
Coming back from Mammoth this past Sunday and flying through a snow
cloud West of the Sierras, I had the Pitot freeze over. I realized it
was frozen when I tried to correct for altitude gained in turbulence
and the airspeed indication didn't increase even as I pushed the nose
down and could hear the relative wind increase. Not a big problem -- I
could see where I was going on the AI, and a minute or less after I
turned Pitot heat on, ASI returned to normal.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Ari.

--
Elections only count as free and trials as fair if you can lose money
betting on the outcome.

Pitot heat power in most airliners I know of is controlled by way of
the squat switch (landing gear) to prevent burnout on the ground.

Javier


"Mike Rapoport" wrote in message thlink.net...
Leave it on all the time. Every checklist for a turbine airplane that I
have seen says to turn it on. All airlines leave it on all the time. Since
the heat is just a resistance element with no moving parts, I doubt that it
will "wear out faster" as others have suggested. Mine have 4600hrs on them
and presumably they have been on all that time.

Mike
MU-2


"K. Ari Krupnikov" wrote in message
...
Coming back from Mammoth this past Sunday and flying through a snow
cloud West of the Sierras, I had the Pitot freeze over. I realized it
was frozen when I tried to correct for altitude gained in turbulence
and the airspeed indication didn't increase even as I pushed the nose
down and could hear the relative wind increase. Not a big problem -- I
could see where I was going on the AI, and a minute or less after I
turned Pitot heat on, ASI returned to normal.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Ari.

--
Elections only count as free and trials as fair if you can lose money
betting on the outcome.

While it has no moving parts, they due "burn out" by overheating. Its a
cigarette
lighter, the filiment can and does burn out, usually caused by overheating.

Also, smaller GA singles will notice the current drain on the system
(espicially if
they have not beefed up the alternator and have a brand new radio stack with
high
powered radios, cd players, etc... ).

I was actually working on a temperature switch setup, one that would allow
you to turn
the switch on all the time, yet would not actually power it if the
temperature was above
say 5C or so. This would significanly help with the burn out, but not the
current draw issue.

Scott

"Mike Rapoport" wrote in message
hlink.net...
Leave it on all the time. Every checklist for a turbine airplane that I
have seen says to turn it on. All airlines leave it on all the time.
Since
the heat is just a resistance element with no moving parts, I doubt that
it
will "wear out faster" as others have suggested. Mine have 4600hrs on
them
and presumably they have been on all that time.

Mike
MU-2


"K. Ari Krupnikov" wrote in message
...
Coming back from Mammoth this past Sunday and flying through a snow
cloud West of the Sierras, I had the Pitot freeze over. I realized it
was frozen when I tried to correct for altitude gained in turbulence
and the airspeed indication didn't increase even as I pushed the nose
down and could hear the relative wind increase. Not a big problem -- I
could see where I was going on the AI, and a minute or less after I
turned Pitot heat on, ASI returned to normal.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Ari.

--
Elections only count as free and trials as fair if you can lose money
betting on the outcome.

I was actually working on a temperature switch setup, one that would allow
you to turn
the switch on all the time, yet would not actually power it if the
temperature was above
say 5C or so.


Something else to go wrong.

Jose

--
(for Email, make the obvious changes in my address)

yes - you don't want to leave it turned on without adequate airflow to
dissipate the heat buildup. The things get hot enough to melt the 1/4"
plastic tubing that connect most of them to the P/S system. I had a P/S
failure just prior to rotation on an ITO in Seattle years ago because of a
looong hold with the heat turned on. Luckily the student in the left seat
had paid attention during training and aborted the takeoff when the airspeed
went to zero. A perfect training lesson for the student and a lesson in
reality for the instructor.

Typically now we turn on the heat as we taxi into position and then turn it
off during the taxi in to the ramp. Feel of the pitot tube some time after
the heat has been on for a while -- but do so carefully because you can get
burnt on some of them.

--
Jim Carter
Seen on a bumper sticker:
If you can read this, thank a teacher
If you can read this in English, thank a soldier.

"K. Ari Krupnikov" wrote in message
...
Coming back from Mammoth this past Sunday and flying through a snow
cloud West of the Sierras, I had the Pitot freeze over. I realized it
was frozen when I tried to correct for altitude gained in turbulence
and the airspeed indication didn't increase even as I pushed the nose
down and could hear the relative wind increase. Not a big problem -- I
could see where I was going on the AI, and a minute or less after I
turned Pitot heat on, ASI returned to normal.

This did raise a question -- is there a good reason Pitot heat isn't
on all the time? It doesn't seem to be a big power drain, and unlike
carb heat does not to my knowledge affect performance. Is there a
reason I shouldn't turn it on when I put transponder on ALT and turn
it off when I shut down electrics before engine shutdown?

Ari.

--
Elections only count as free and trials as fair if you can lose money
betting on the outcome.