alt. static.

[[email protected]]

I was preparing to fly a cessna 172SP the other day and as I usually
do I pulled the alt.static expecting a small wiggle in the gauges. And
got nothing. This was the first time I i got no response from the
gauges. I was told by somebody at the front desk this was common and
that many of the 172's show no movement at all. But.. if this is so..
how can I be certain the alt.static would work when I needed it.


Thanks in advance.

[Bob Gardner]

On the ground, the pressure inside the airplane and outside of the airplane
are the same...why would you expect the needle to wiggle?

Bob Gardner

> wrote in message
oups.com...
>I was preparing to fly a cessna 172SP the other day and as I usually
> do I pulled the alt.static expecting a small wiggle in the gauges. And
> got nothing. This was the first time I i got no response from the
> gauges. I was told by somebody at the front desk this was common and
> that many of the 172's show no movement at all. But.. if this is so..
> how can I be certain the alt.static would work when I needed it.
>
>
> Thanks in advance.
>

[[email protected]]

Bob Gardner > wrote:
> On the ground, the pressure inside the airplane and outside of the airplane
> are the same...why would you expect the needle to wiggle?

> Bob Gardner

> > wrote in message
> oups.com...
> >I was preparing to fly a cessna 172SP the other day and as I usually
> > do I pulled the alt.static expecting a small wiggle in the gauges. And
> > got nothing. This was the first time I i got no response from the
> > gauges. I was told by somebody at the front desk this was common and
> > that many of the 172's show no movement at all. But.. if this is so..
> > how can I be certain the alt.static would work when I needed it.
> >
> >
> > Thanks in advance.

The act of moving the valve causes a slight, transitory pressure
change.

That causes the VSI to wiggle one way when you open it then the other
when you close it.

On some airplanes the prop wash will cause a very slight differntial
between the inside and outside which will also cause a slight
wiggle in the VSI.

--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

On Nov 1, 8:55 am, "Bob Gardner" > wrote:
> On the ground, the pressure inside the airplane and outside of the airplane
> are the same...why would you expect the needle to wiggle?
>
> Bob Gardner
>

Are you indicating it won't? i.e. are you saying in your experience it
does not wiggle?

I expect it to move because that is what I was taught. And I have
flown a lot of these and have never seen it not "wiggle".

I am interested in how I know the knob works. Is looking for the
wiggle a reliable way to tell if the alt. static system is going to
function when I need it. If not how do I know. Should the item have
been squawked or simply noted as an observation.

[Newps]

wrote:

> On Nov 1, 8:55 am, "Bob Gardner" > wrote:
>
>>On the ground, the pressure inside the airplane and outside of the airplane
>>are the same...why would you expect the needle to wiggle?
>>
>>Bob Gardner
>>
>
>
> Are you indicating it won't? i.e. are you saying in your experience it
> does not wiggle?
>
> I expect it to move because that is what I was taught. And I have
> flown a lot of these and have never seen it not "wiggle".
>
> I am interested in how I know the knob works. Is looking for the
> wiggle a reliable way to tell if the alt. static system is going to
> function when I need it. If not how do I know. Should the item have
> been squawked or simply noted as an observation.
>
>


In the Cessna's I've seen the static port is near the pilots knees. If
this is the case in the plane you're talking about take a look under the
panel at the connection to this port. If you can reach it from the
pilots seat then all you have to do is pull it off the fitting and you
have alternate air.

[Judah]

Newps > wrote in
:

> In the Cessna's I've seen the static port is near the pilots knees. If
> this is the case in the plane you're talking about take a look under the
> panel at the connection to this port. If you can reach it from the
> pilots seat then all you have to do is pull it off the fitting and you
> have alternate air.

Alternatively, break the glass on the VSI.

[Newps]

Judah wrote:
> Newps > wrote in
> :
>
>
>>In the Cessna's I've seen the static port is near the pilots knees. If
>>this is the case in the plane you're talking about take a look under the
>>panel at the connection to this port. If you can reach it from the
>>pilots seat then all you have to do is pull it off the fitting and you
>>have alternate air.
>
>
> Alternatively, break the glass on the VSI.



The smart pilot finds where the pitot line runs instead for two reasons.
It's harder than hell to break the glass and second that costs money
if you actually can break it.

[[email protected]]

Judah > wrote:
> Newps > wrote in
> :

> > In the Cessna's I've seen the static port is near the pilots knees. If
> > this is the case in the plane you're talking about take a look under the
> > panel at the connection to this port. If you can reach it from the
> > pilots seat then all you have to do is pull it off the fitting and you
> > have alternate air.

> Alternatively, break the glass on the VSI.

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

--
Jim Pennino

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[Judah]

wrote in :

> 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?

[[email protected]]

Judah > wrote:
> wrote in :

> > 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

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[JGalban via AviationKB.com]

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

[[email protected]]

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.

[JGalban via AviationKB.com]

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

[Andrew Sarangan]

On Nov 1, 12:58 am, wrote:
> I was preparing to fly a cessna 172SP the other day and as I usually
> do I pulled the alt.static expecting a small wiggle in the gauges. And
> got nothing. This was the first time I i got no response from the
> gauges. I was told by somebody at the front desk this was common and
> that many of the 172's show no movement at all. But.. if this is so..
> how can I be certain the alt.static would work when I needed it.
>
> Thanks in advance.

I have seen some airplanes show a small wiggle, and some that don't
when the static port is turned on or off. There is no easy way to
positively verify that your alternate static is working. If you are up
to it, you could suck on the static port and ask someone to verify
whether the VSI is showing a climb. Then repeat with the alt static
open. The latter should not show a climb. Or get a suction for this
purpose. Just a thought. I have never done it this way.

[[email protected]]

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

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[Peter Clark]

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?

[[email protected]]

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

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[[email protected]]

On Nov 2, 3:55 pm, Andrew Sarangan > wrote:
> On Nov 1, 12:58 am, wrote:
>
> > I was preparing to fly a cessna 172SP the other day and as I usually
> > do I pulled the alt.static expecting a small wiggle in the gauges. And
> > got nothing. This was the first time I i got no response from the
> > gauges. I was told by somebody at the front desk this was common and
> > that many of the 172's show no movement at all. But.. if this is so..
> > how can I be certain the alt.static would work when I needed it.
>
> > Thanks in advance.
>
> I have seen some airplanes show a small wiggle, and some that don't
> when the static port is turned on or off. There is no easy way to
> positively verify that your alternate static is working. If you are up
> to it, you could suck on the static port and ask someone to verify
> whether the VSI is showing a climb. Then repeat with the alt static
> open. The latter should not show a climb. Or get a suction for this
> purpose. Just a thought. I have never done it this way.

To clarify i have flown - rented - this aircraft a lot and it always
wiggled. The aircraft is a 172SP.

I would not cancel a VFR flight in the area for the lack of
alt.static, but as my CFI said - I asked him this question too - IFR
would be a different story.

[C J Campbell[_1_]]

On 2007-11-02 15:55:56 -0700, Andrew Sarangan > said:

> On Nov 1, 12:58 am, wrote:
>> I was preparing to fly a cessna 172SP the other day and as I usually
>> do I pulled the alt.static expecting a small wiggle in the gauges. And
>> got nothing. This was the first time I i got no response from the
>> gauges. I was told by somebody at the front desk this was common and
>> that many of the 172's show no movement at all. But.. if this is so..
>> how can I be certain the alt.static would work when I needed it.
>>
>> Thanks in advance.
>
> I have seen some airplanes show a small wiggle, and some that don't
> when the static port is turned on or off. There is no easy way to
> positively verify that your alternate static is working. If you are up
> to it, you could suck on the static port and ask someone to verify
> whether the VSI is showing a climb. Then repeat with the alt static
> open. The latter should not show a climb. Or get a suction for this
> purpose. Just a thought. I have never done it this way.

You don't want to, either. I have had avionics guys tell me that this
can damage the instruments.
--
Waddling Eagle
World Famous Flight Instructor

[B A R R Y]

On Sat, 03 Nov 2007 15:05:03 GMT, wrote:

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


Every airplane that I've flown that's so equipped did exactly that.

[Andrew Sarangan]

On Nov 3, 3:01 pm, C J Campbell >
wrote:
> On 2007-11-02 15:55:56 -0700, Andrew Sarangan > said:
>
>
>
>
>
> > On Nov 1, 12:58 am, wrote:
> >> I was preparing to fly a cessna 172SP the other day and as I usually
> >> do I pulled the alt.static expecting a small wiggle in the gauges. And
> >> got nothing. This was the first time I i got no response from the
> >> gauges. I was told by somebody at the front desk this was common and
> >> that many of the 172's show no movement at all. But.. if this is so..
> >> how can I be certain the alt.static would work when I needed it.
>
> >> Thanks in advance.
>
> > I have seen some airplanes show a small wiggle, and some that don't
> > when the static port is turned on or off. There is no easy way to
> > positively verify that your alternate static is working. If you are up
> > to it, you could suck on the static port and ask someone to verify
> > whether the VSI is showing a climb. Then repeat with the alt static
> > open. The latter should not show a climb. Or get a suction for this
> > purpose. Just a thought. I have never done it this way.
>
> You don't want to, either. I have had avionics guys tell me that this
> can damage the instruments.
> --

Why would applying suction on the static port damage anything? Isn't
that what the atmosphere is doing during a climb?

[[email protected]]

Andrew Sarangan > wrote:
> On Nov 3, 3:01 pm, C J Campbell >
> wrote:
> > On 2007-11-02 15:55:56 -0700, Andrew Sarangan > said:
> >
> >
> >
> >
> >
> > > On Nov 1, 12:58 am, wrote:
> > >> I was preparing to fly a cessna 172SP the other day and as I usually
> > >> do I pulled the alt.static expecting a small wiggle in the gauges. And
> > >> got nothing. This was the first time I i got no response from the
> > >> gauges. I was told by somebody at the front desk this was common and
> > >> that many of the 172's show no movement at all. But.. if this is so..
> > >> how can I be certain the alt.static would work when I needed it.
> >
> > >> Thanks in advance.
> >
> > > I have seen some airplanes show a small wiggle, and some that don't
> > > when the static port is turned on or off. There is no easy way to
> > > positively verify that your alternate static is working. If you are up
> > > to it, you could suck on the static port and ask someone to verify
> > > whether the VSI is showing a climb. Then repeat with the alt static
> > > open. The latter should not show a climb. Or get a suction for this
> > > purpose. Just a thought. I have never done it this way.
> >
> > You don't want to, either. I have had avionics guys tell me that this
> > can damage the instruments.
> > --

> Why would applying suction on the static port damage anything? Isn't
> that what the atmosphere is doing during a climb?

Like everything else in life; depends on how hard you suck...

--
Jim Pennino

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