"Bob F." wrote in
:

"Bob F." wrote in message
. ..
"Dallas" wrote in message
...
On Fri, 15 Aug 2008 23:02:16 +0000 (UTC), Bertie the Bunyip wrote:

There is the question. I'm in a mood today. Have you flown your
favorite aircraft with zero or near zero indicated airspeed?

I haven't done it, but flying through some icing with the pitot heat
off should do the trick.

So... what's your answer?

--
Dallas


If the pitot and weep hole ice over, the airspeed will not change
until you change altitude.

--
Regards, BobF.


I had these airspeed experiences:
1. We were moving gliders from our winter storage location to our
filed of operation near Seattle. It was the first flight in the
morning. This was an extremely short field take off. We had a
specially developed technique to handle this including a very short
tow rope. I was towing using a Pawnee and noticed the AS to be very
sluggish and it stopped at about 50 Kts. I was committed for this
size field and with a glider behind me to boot. I wasn't sure of how
fast I was going and just depended on experience, aircraft feel and
field length. I just cleared the fence. We climbed to our agreed
altitude, and kept a known throttle setting. When we got near our
final field, the glider released. My ASI was still indicating abt 60
kts but not changing except with altitude. I did a couple of stalls
in order to refresh myself of the nuances and feel of the Pawnee and
then returned to the field and made an uneventful landing. I later
talked to the glider pilot and to my delight he said he didn't notice
anything out of the ordinary during the whole event. A bug was found
wedged in the pitot tube.

2. I had an instrument student on a 172 long cross country from SJC.
We got clearance, took off, and I noticed the ASI behaving very
similarly. It was indicating low but for some reason, the student
said nothing. Just before entering the cloud base, I pushed it over,
asked the student to return for a landing, negotiated this all with
the tower and the student made an airspeed indicator failure landing,
a little hot, but just fine. Taxied back (still indicating about 40
kts) to the flight school and pried out another bug.

A story I know of:
727, pitot heat breaker tripped, pilot didn't know. Pitot (actually
called an "air data sensor") froze over and as he was climbing the ASI
was now behaving like an altimeter. As the AS was increasing, he was
increasing pitch. It wasn't until he reached "stick shaker" did he
put it all together. There might be another variation and more
details to this story, since I now only remember the lesson and not
the facts.



There was a 727 that crashed because of iced over pitot tubes. the pitot
heat wasn't truned on. The early pitot heat swtiching gave you greens if
the heat was n, bu tnothing if it was turned off. All Boeings were
modified to have a big amber light on if the heat was left off and
indications throughout the industry were rethought to ultimately develop
the "dark cockpits" we have today, mostly due to that accident.

Bertie