alt. static.

Judah wrote:
wrote in news

Neither of which seem to me to be very good preflight procedures, which
is what the question is about.

Do you intend to imply that if your alternatic air source does not make the
VSI wiggle, you would cancel your flight failing a suitable pre-flight
procedure?

No, I'm outright saying that pulling hoses or breaking the glass on
the VSI isn't a viable preflight procedure.

And since I've never seen a 172 where the VSI didn't wiggle when I
turned the alternate on and off, I would want to know why it didn't
before I flew it.

--
Jim Pennino

Remove .spam.sux to reply.

wrote:

And since I've never seen a 172 where the VSI didn't wiggle when I
turned the alternate on and off, I would want to know why it didn't
before I flew it.


On the ground, there doesn't always have to be a significant difference
between cabin air pressure and outside pressure. I'd recommend trying the
check in flight. If you don't see any difference there, then you've got a
leak in the static system.

John Galban=====N4BQ (PA28-180)

--
Message posted via http://www.aviationkb.com

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

And since I've never seen a 172 where the VSI didn't wiggle when I
turned the alternate on and off, I would want to know why it didn't
before I flew it.


On the ground, there doesn't always have to be a significant difference
between cabin air pressure and outside pressure. I'd recommend trying the
check in flight. If you don't see any difference there, then you've got a
leak in the static system.

Correct me if I'm wrong here, but isn't a preflight supposed to be done
before you take off?

And one more time...

Since I've never seen a 172 where the VSI didn't wiggle when I turned
the alternate on and off on the ground, I would want to know why it didn't
before I flew it.

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation

--
Jim Pennino

Remove .spam.sux to reply.

wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Seriously, I suspect that the 172 you're talking about probably does have a
static leak into the cabin. If you want to verify that in order to get it
fixed, flipping to the alt static at speed will be most convincing to
maintenance personnel. Another way to check for a cabin static leak is to
open a window (if allowed) in flight. If your VSI, airspeed and altimeter
needles jump, you've got a leak in the cabin.

On the ground, some aircraft do not experience a perceptable indication due
to the location of the exterior static port.

John Galban=====N4BQ (PA28-180)

--
Message posted via http://www.aviationkb.com

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Every CFI I had while a student said to do it and every 172 I've ever
flown does it.

Specifically, at the beginning of the preflight walk around, after
ensuring the master is off, pull the alternate static control out, then
shove it in to make sure it is off; the VSI should wiggle.

That's while standing in the open door.

Seriously, I suspect that the 172 you're talking about probably does have a
static leak into the cabin.

I am not the one that posed the original question nor have I flown a 172
newer than a P model.

If you want to verify that in order to get it
fixed, flipping to the alt static at speed will be most convincing to
maintenance personnel. Another way to check for a cabin static leak is to
open a window (if allowed) in flight. If your VSI, airspeed and altimeter
needles jump, you've got a leak in the cabin.

On the ground, some aircraft do not experience a perceptable indication due
to the location of the exterior static port.

Maybe, but the original poster was talking specifically about a 172.

--
Jim Pennino

Remove .spam.sux to reply.

On Sat, 03 Nov 2007 00:05:02 GMT, wrote:

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Every CFI I had while a student said to do it and every 172 I've ever
flown does it.

Specifically, at the beginning of the preflight walk around, after
ensuring the master is off, pull the alternate static control out, then
shove it in to make sure it is off; the VSI should wiggle.

That's while standing in the open door.

Same for every 172 and 182 I've flown. Isn't the action of actuating
the flaper in the selector box (or t or whatever it is that it's
moving) creating a little pressure wave which is what makes the
needles move?

Peter Clark wrote:
On Sat, 03 Nov 2007 00:05:02 GMT, wrote:

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Every CFI I had while a student said to do it and every 172 I've ever
flown does it.

Specifically, at the beginning of the preflight walk around, after
ensuring the master is off, pull the alternate static control out, then
shove it in to make sure it is off; the VSI should wiggle.

That's while standing in the open door.

Same for every 172 and 182 I've flown. Isn't the action of actuating
the flaper in the selector box (or t or whatever it is that it's
moving) creating a little pressure wave which is what makes the
needles move?

That's what I was told and that if the systems working, the needle
bounces one way when opened and the other when closed.

--
Jim Pennino

Remove .spam.sux to reply.