Pitot/Static/Transponder Problem

[Kyle Boatright]

I was using Flight Following yesterday and was reminded of a problem that my
RV has displayed for a long time: The transponder and altimeter do not
agree. In general, ATC sees my altitude as about 200' lower than what is
shown on my altimeter.

A couple of facts:

- The transponder/encoder always pass their certification checks.

- The pitot/static system is installed per plans.

Any thoughts?

KB

[Bill Daniels]

Tell ATC that you aren't 200' low, they're 200' too high:) (Actually,
I've encountered 200' differences when switched to a new ATC sector -
somebody's not calibrated.)

Seriously, if you set your altimeter to the local AWOS/ATIS/ASOS does it
read the published field elevation? If not, the altimeter needs
calibration. If so, it's not the instrument.

Presumably, it's not the encoder if it passes the bi-annual field check but
do you know if your avionics shop has calibrated their transponder checking
equipment?

When was the last pitot/static check done? Do you have a leak in the static
tubing? If there is a leak in the static system, the altimeter may be
reading cabin pressure which 'could' be higher than a true static.

Oh the fun of chasing gremlins...

Bill Daniels

"Kyle Boatright" > wrote in message
...
>I was using Flight Following yesterday and was reminded of a problem that
>my RV has displayed for a long time: The transponder and altimeter do not
>agree. In general, ATC sees my altitude as about 200' lower than what is
>shown on my altimeter.
>
> A couple of facts:
>
> - The transponder/encoder always pass their certification checks.
>
> - The pitot/static system is installed per plans.
>
> Any thoughts?
>
> KB
>

[quietguy]

Building to the plans doesn't guarantee accurate static pressure
readings; the system is quite sensitive to tiny plane-to-plane
variations. And the official calibration check with the airplane
stationary wouldn't catch an in-flight static-pressure error.

Have an observer watch the altimeter during takeoff and landing ground
rolls: if it changes from a standstill to takeoff speed and then
changes in the opposite sense during the landing roll (the VSI would
also depart from zero at these times), then you'll know that there's a
static-pressure measurement error built into your installation. The
amount of the spurious altitude change would be about 200 ft times the
ratio of takeoff/landing speed to cruise speed; e.g., if the speed
ratio is about 1/3, then the change would be 60-70 ft.

The static port(s) wouldn't necessarily have to be relocated if this
error is present; you may be able to tweak the readings sufficiently
with a wire-and-tape "trip strip" just ahead of the port (to lower the
static reading) or behind it (to raise the reading). Even some store-
bought airplanes have such cheap-and-easy fixes near their ports.
Just keep experimenting with the height and position of the strip
until the airplane doesn't "climb" or "descend" while trundling along
a level runway.

[Ron Wanttaja]

On Sun, 05 Aug 2007 10:27:25 -0700, quietguy > wrote:

>Building to the plans doesn't guarantee accurate static pressure
>readings; the system is quite sensitive to tiny plane-to-plane
>variations. And the official calibration check with the airplane
>stationary wouldn't catch an in-flight static-pressure error.

Yes, but: If the encoder and the altimeter are using the same static source,
both should be in error the same amount. Kyle's problem is a split indication;
the encoder is sensing a different altitude than the altimeter.

This tends to argue that the problem is a leak related to the altimeter itself,
not in the static system. Perhaps the altimeter has a leak that only manifests
itself when it's being vibrated (i.e., the engine running).

My Microair transponder gives me a readout of the altitude that's being sent to
ATC. I can set the A/C altimeter to 29.92 and compare. That's how I discovered
my encoder had gone south two months back; the altitude readout wasn't matching
the altimeter.

Ron Wanttaja

[[email protected]]

The encoder gives an uncorrected altitude. You altimeter is
corrected when you set it for barometric pressure at the beginning of
flight. ATC receives the signal from the encoder/transponder and
corrects it for the local pressure. If you are some distance from
their station, there could easily be a 0.2" Hg pressure differential
that would result in a 200' differential (one inch Hg per 1000' of
altitude).
So even if you are using the altimeter setting they give you, I
wouldn't expect perfect correlation if there's a pressure gradient
beteen you and them.

Dan

[Kyle Boatright]

> wrote in message
oups.com...
>
> The encoder gives an uncorrected altitude. You altimeter is
> corrected when you set it for barometric pressure at the beginning of
> flight. ATC receives the signal from the encoder/transponder and
> corrects it for the local pressure. If you are some distance from
> their station, there could easily be a 0.2" Hg pressure differential
> that would result in a 200' differential (one inch Hg per 1000' of
> altitude).
> So even if you are using the altimeter setting they give you, I
> wouldn't expect perfect correlation if there's a pressure gradient
> beteen you and them.
>
> Dan

If it was an intermittent problem, your theory would be plausible, but since
I see the same problem virtually every time I deal with ATC, I'm thinking it
is a hardware problem. The only issue is which piece of hardware? ;-)

KB

[Kyle Boatright]

"Bill Daniels" <bildan@comcast-dot-net> wrote in message
. ..
> Tell ATC that you aren't 200' low, they're 200' too high:) (Actually,
> I've encountered 200' differences when switched to a new ATC sector -
> somebody's not calibrated.)
>
> Seriously, if you set your altimeter to the local AWOS/ATIS/ASOS does it
> read the published field elevation? If not, the altimeter needs
> calibration. If so, it's not the instrument.

The altimeter was reworked a couple of years ago because it got "sticky".
It came back with a yellow tag and a test card indicating it was calibrated
within VFR limits. Since the altitude discrepancy problem existed before
the altimeter rebuild and has persisted since, I'm guessing the Altimeter is
good.

>
> Presumably, it's not the encoder if it passes the bi-annual field check
> but do you know if your avionics shop has calibrated their transponder
> checking equipment?

No idea, but doesn't the shop have to calibrate its equipment to remain a
certified shop?

>
> When was the last pitot/static check done? Do you have a leak in the
> static tubing? If there is a leak in the static system, the altimeter may
> be reading cabin pressure which 'could' be higher than a true static.

I've never done a pitot/static check. Is there a DIY procedure for that?

>
> Oh the fun of chasing gremlins...

You got that right!

>
> Bill Daniels
>
> "Kyle Boatright" > wrote in message
> ...
>>I was using Flight Following yesterday and was reminded of a problem that
>>my RV has displayed for a long time: The transponder and altimeter do not
>>agree. In general, ATC sees my altitude as about 200' lower than what is
>>shown on my altimeter.
>>
>> A couple of facts:
>>
>> - The transponder/encoder always pass their certification checks.
>>
>> - The pitot/static system is installed per plans.
>>
>> Any thoughts?
>>
>> KB
>>
>
>

[cavelamb himself[_3_]]

Ron Wanttaja wrote:
> On Sun, 05 Aug 2007 10:27:25 -0700, quietguy > wrote:
>
>
>>Building to the plans doesn't guarantee accurate static pressure
>>readings; the system is quite sensitive to tiny plane-to-plane
>>variations. And the official calibration check with the airplane
>>stationary wouldn't catch an in-flight static-pressure error.
>
>
> Yes, but: If the encoder and the altimeter are using the same static source,
> both should be in error the same amount. Kyle's problem is a split indication;
> the encoder is sensing a different altitude than the altimeter.
>
> This tends to argue that the problem is a leak related to the altimeter itself,
> not in the static system. Perhaps the altimeter has a leak that only manifests
> itself when it's being vibrated (i.e., the engine running).
>
> My Microair transponder gives me a readout of the altitude that's being sent to
> ATC. I can set the A/C altimeter to 29.92 and compare. That's how I discovered
> my encoder had gone south two months back; the altitude readout wasn't matching
> the altimeter.
>
> Ron Wanttaja

Are your transponder and altimeter physically close to each other?

(How far apart could they be in a Fly Baby??)

In larger planes it's not uncommon for the encoder to be mounted behind
the seats or such. Quite far from the altimeter - with a lot of extra
hose between them.

Just a thought...


Richard

[Bill Daniels]

"Kyle Boatright" > wrote in message
. ..
>
> "Bill Daniels" <bildan@comcast-dot-net> wrote in message
> . ..
>> Tell ATC that you aren't 200' low, they're 200' too high:) (Actually,
>> I've encountered 200' differences when switched to a new ATC sector -
>> somebody's not calibrated.)
>>
>> Seriously, if you set your altimeter to the local AWOS/ATIS/ASOS does it
>> read the published field elevation? If not, the altimeter needs
>> calibration. If so, it's not the instrument.
>
> The altimeter was reworked a couple of years ago because it got "sticky".
> It came back with a yellow tag and a test card indicating it was
> calibrated within VFR limits. Since the altitude discrepancy problem
> existed before the altimeter rebuild and has persisted since, I'm guessing
> the Altimeter is good.

It's a good bet that a yellow tagged altimeter is OK but I'd still check it
against field elevation. In fact, it's a good idea to do it each time you
do a pre-flight check. Just set the local altimeter pressure and see if the
altimeter indicates field elevation.

The most likely problem is a leak in the static system. If you're up to it
there's a simple check. Get a large plastic hypo syringe and carefully "T"
it into the static tubing behind the panel using a fish tank tubing "T" and
Tygon tubing - make sure all fittings are leak free. Cover the static ports
with electrical tape to seal them off. SLOWLY inject air with the syringe
until the altimeter reads 1000 feet lower than field elevation. Stop
injecting air and watch the altimeter. If there's a leak, the altimeter
will slowly return to field elevation. The ROC will indicate the rate of
the leak.

Realize that the leak can be inside an instrument. I've seen several ROC
instruments with internal leaks (Usually the glass gasket is bad which can
be determined with a soap solution.) but the ASI or even the altimeter
itself can be the culprit. If there is a leak, look for bubbles with soap
solution until you find where it is.

BTW, there's an old glider pilot trick to sealing Tygon tubing to instrument
nipples. Go to a veternary supply store and buy a bag of the rubber
bands(green O-rings) used to castrate sheep (I'm not kidding!) These are
just the right size to slip over the outside of the Tygon after it is pushed
onto the instrument nipple. Put the O-ring over the tubing before pushing
it onto the instrument nipple then roll it over the nipple. It makes a
reliable gas-tight fit even when the Tygon gets old and yellowed.

Bill Daniels

[Kyle Boatright]

"Bill Daniels" <bildan@comcast-dot-net> wrote in message
. ..
>
> "Kyle Boatright" > wrote in message
> . ..
>>
>> "Bill Daniels" <bildan@comcast-dot-net> wrote in message
>> . ..
>>> Tell ATC that you aren't 200' low, they're 200' too high:)
>>> (Actually, I've encountered 200' differences when switched to a new ATC
>>> sector - somebody's not calibrated.)
>>>
>>> Seriously, if you set your altimeter to the local AWOS/ATIS/ASOS does it
>>> read the published field elevation? If not, the altimeter needs
>>> calibration. If so, it's not the instrument.
>>
>> The altimeter was reworked a couple of years ago because it got "sticky".
>> It came back with a yellow tag and a test card indicating it was
>> calibrated within VFR limits. Since the altitude discrepancy problem
>> existed before the altimeter rebuild and has persisted since, I'm
>> guessing the Altimeter is good.
>
> It's a good bet that a yellow tagged altimeter is OK but I'd still check
> it against field elevation. In fact, it's a good idea to do it each time
> you do a pre-flight check. Just set the local altimeter pressure and see
> if the altimeter indicates field elevation.

I should have mentioned before that the altimeter is close to the field
elevation when on the ground. Well within VFR limits.

One interesting test would be a low altitude pass down the runway at cruise
power and speed. If I'm 50' above the field and the altimeter shows field
level + 50' (or thereabouts) what would that tell me?

A basic question: If there was a problem with the static system, wouldn't
that cause the same discrepancy in both the altimeter and transponder?

>
> The most likely problem is a leak in the static system. If you're up to
> it there's a simple check. Get a large plastic hypo syringe and carefully
> "T" it into the static tubing behind the panel using a fish tank tubing
> "T" and Tygon tubing - make sure all fittings are leak free. Cover the
> static ports with electrical tape to seal them off. SLOWLY inject air
> with the syringe until the altimeter reads 1000 feet lower than field
> elevation. Stop injecting air and watch the altimeter. If there's a
> leak, the altimeter will slowly return to field elevation. The ROC will
> indicate the rate of the leak.

I was trying to come up with a technique to do this, and this one sounds
like a winner. There is a location in the baggage compartment where it is
easy to get to the static tubing...

>
> Realize that the leak can be inside an instrument. I've seen several ROC
> instruments with internal leaks (Usually the glass gasket is bad which can
> be determined with a soap solution.) but the ASI or even the altimeter
> itself can be the culprit. If there is a leak, look for bubbles with soap
> solution until you find where it is.
>
> BTW, there's an old glider pilot trick to sealing Tygon tubing to
> instrument nipples. Go to a veternary supply store and buy a bag of the
> rubber bands(green O-rings) used to castrate sheep (I'm not kidding!)
> These are just the right size to slip over the outside of the Tygon after
> it is pushed onto the instrument nipple. Put the O-ring over the tubing
> before pushing it onto the instrument nipple then roll it over the nipple.
> It makes a reliable gas-tight fit even when the Tygon gets old and
> yellowed.
>
> Bill Daniels

Thanks for the ideas.

KB

[Capt. Geoffrey Thorpe]

"Kyle Boatright" > wrote in message
...
>
<...> I should have mentioned before that the altimeter is close to the
field
> elevation when on the ground. Well within VFR limits.
>
> One interesting test would be a low altitude pass down the runway at
> cruise power and speed. If I'm 50' above the field and the altimeter shows
> field level + 50' (or thereabouts) what would that tell me?
>
> A basic question: If there was a problem with the static system, wouldn't
> that cause the same discrepancy in both the altimeter and transponder?
<...>

That seems likely as far as static sytem design is concerned (e.g. static
port location).

If they differ only in flight, then they probably aren't seeing the same
static source due to kinks and leaks. I assume that both are really
connected to the static source (You have looked, right? No hose has fallen
off?)

Have the encoder output compared to the altimeter while sitting on the
ground - if they are the same, you have a plumbing problem. If they are
different, the problem is in the instruments, eh?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Dave[_16_]]

Capt. Geoffrey Thorpe wrote:
> "Kyle Boatright" > wrote in message
> ...
> <...> I should have mentioned before that the altimeter is close to the
> field
>> elevation when on the ground. Well within VFR limits.
>>
>> One interesting test would be a low altitude pass down the runway at
>> cruise power and speed. If I'm 50' above the field and the altimeter shows
>> field level + 50' (or thereabouts) what would that tell me?
>>
>> A basic question: If there was a problem with the static system, wouldn't
>> that cause the same discrepancy in both the altimeter and transponder?
> <...>
>
> That seems likely as far as static sytem design is concerned (e.g. static
> port location).
>
> If they differ only in flight, then they probably aren't seeing the same
> static source due to kinks and leaks. I assume that both are really
> connected to the static source (You have looked, right? No hose has fallen
> off?)
>
> Have the encoder output compared to the altimeter while sitting on the
> ground - if they are the same, you have a plumbing problem. If they are
> different, the problem is in the instruments, eh?
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
>
Where the static port is located has no bearing on this issue. There
could be a kink/clog like Geoff indicates but it would need to be
between both the instruments. There could also be water in the static
line somewhere between where the altimeter and encoder are.
A leak won't do it since the altimeter and encoder are at the same
potential. They will both just read the same erroneous altitude. Also,
your airspeed would be off quite a bit since it shares the static system.

Either the altimeter or encoder is off. Your allowed 125 foot deviation
between the two to be legal.
You need to get the system checked and recalibrated. The encoder can be
recalibrated on site if it is off, but the altimeter will need to go to
the shop.

My guess if the altimeter reads the correct baro at field elevation,
then the encoder is the problem.
And if it's suddenly off by 200 feet, then it probably has more of an
issue than a calibration would permanently fix.

If your in the Dallas area, let me know and I can give you a hand to
figure this out. I run/own a repair station for doing this sort of thing.

A cheap and dirty way to check for static leaks (that makes a
difference) is to open a window in flight and see if the airspeed and
altimeter jumps around. If the system is tight, there should be no change.

Good luck

Dave

www.craigmileaviation.com

[Kyle Boatright]

"Dave" > wrote in message
. net...

<<<snip>>>
> Either the altimeter or encoder is off. Your allowed 125 foot deviation
> between the two to be legal.
> You need to get the system checked and recalibrated. The encoder can be
> recalibrated on site if it is off, but the altimeter will need to go to
> the shop.
>
> My guess if the altimeter reads the correct baro at field elevation, then
> the encoder is the problem.
> And if it's suddenly off by 200 feet, then it probably has more of an
> issue than a calibration would permanently fix.

This is a problem that has seemingly existed for years. I'm just getting
around to addressing it.

>
> If your in the Dallas area, let me know and I can give you a hand to
> figure this out. I run/own a repair station for doing this sort of thing.
>
> A cheap and dirty way to check for static leaks (that makes a difference)
> is to open a window in flight and see if the airspeed and altimeter jumps
> around. If the system is tight, there should be no change.

That or open or close the fresh air vents.

>
> Good luck
>
> Dave
>
> www.craigmileaviation.com

I'm not in Dallas, but appreciate the advise.

KB

[Dave[_16_]]

Kyle Boatright wrote:
> "Dave" > wrote in message
> . net...
>
>> My guess if the altimeter reads the correct baro at field elevation, then
>> the encoder is the problem.
>> And if it's suddenly off by 200 feet, then it probably has more of an
>> issue than a calibration would permanently fix.
>
> This is a problem that has seemingly existed for years. I'm just getting
> around to addressing it.
>
>
> That or open or close the fresh air vents.
>

>
> KB
>
>

Kyle,

What type of certification did you get? IFR or VFR?

[Kyle Boatright]

"Dave" > wrote in message
. net...
> Kyle Boatright wrote:
>> "Dave" > wrote in message
>> . net...
>>
>>> My guess if the altimeter reads the correct baro at field elevation,
>>> then the encoder is the problem.
>>> And if it's suddenly off by 200 feet, then it probably has more of an
>>> issue than a calibration would permanently fix.
>>
>> This is a problem that has seemingly existed for years. I'm just getting
>> around to addressing it.
>>
>>
>> That or open or close the fresh air vents.
>>
>
>>
>> KB
>
> Kyle,
>
> What type of certification did you get? IFR or VFR?

VFR

[Dave[_16_]]

>>
>> What type of certification did you get? IFR or VFR?
>
> VFR
>
>

There's no requirement to verify/validate mode c correlation with the
altimeter for the vfr check. (91.413)
It is strictly a stand alone transponder check.

The encoder check is only a requirement for the 91.411 check. I offer
two types of VFR checks, one for only 91.413 and the other with
altimeter and encoder correlation. Some owners want to know whats being
sent out on mode c, and others don't.

Next time you get yours done, ask for the mode c check with it.

Dave

[Rich S.[_1_]]

"Dave" > wrote in message
. net...
(snip)
> Either the altimeter or encoder is off. Your allowed 125 foot deviation
> between the two to be legal.
(snip)

Hmmm . . . interesting. Sometimes I fly over a local airport where the
controlled airspace tops out at 2,800'. Over that is Class B airspace with a
floor of 3,000'. So, I fly at 2,900' and figure I'm okay.

If my encoder is 125' different than the altimeter reading, I could be
reporting to either the tower or to ATC that I was infringing on their
airspace. Come to think of it, last time I flew over that tower (at 2,900'),
I requested a transponder check and they reported that I was showing 2,800'.
They didn't seem to get upset.

IIRC, the encoder reports in 100' increments, so I guess mine could be
anywhere from 49' to 149' off the altimeter. (it is VFR certified BTW).

Rich S.

[Dave[_16_]]

Rich S. wrote:
> "Dave" > wrote in message
> . net...
> (snip)
>> Either the altimeter or encoder is off. Your allowed 125 foot deviation
>> between the two to be legal.
> (snip)
>
> Hmmm . . . interesting. Sometimes I fly over a local airport where the
> controlled airspace tops out at 2,800'. Over that is Class B airspace with a
> floor of 3,000'. So, I fly at 2,900' and figure I'm okay.
>
> If my encoder is 125' different than the altimeter reading, I could be
> reporting to either the tower or to ATC that I was infringing on their
> airspace. Come to think of it, last time I flew over that tower (at 2,900'),
> I requested a transponder check and they reported that I was showing 2,800'.
> They didn't seem to get upset.
>
> IIRC, the encoder reports in 100' increments, so I guess mine could be
> anywhere from 49' to 149' off the altimeter. (it is VFR certified BTW).
>
> Rich S.
>
>
Yep.
If you think about it if you fly at 2990' where class B airspace is at
3000', you could be squawking 3100 feet and be legal, sort of.
I don't know what altitude they can really bust you for, but you could
be totally legal and bust "B" airspace.

Does anybody have a read on what the ATC regulations are for this sort
of thing?

And one more tidbit, 91.217 says that the altimeter and encoder need to
be within 125' of each other, but no nothing to the accuracy of either
device. So if both your encoder and altimeter are off by 1000', they are
legal.



Dave
www.craigmileaviation.com
Dallas

[Harvey Spencer]

Maybe some friction/hysteresis in the altimeter not showing up during the
altimiter check, but not likely.
Maybe some strange internal pressure/vacuum in the cockpit in flight
combined with a leaking static
system, but you passed the static test you say.
You should try and tie it down to which, if either, is right and wrong.
Does the altimeter indicate field altitude when
you set the Kollsman window to the ATIS altimeter setting? One way to get a
pretty good altitude check if you can fly
the glideslope with accuracy and if the plane is so equiped is to pass over
the outer maker with the GS needle dead nuts centered and compare the
crossing altitude with what is
indicated on the approach plate.
"Kyle Boatright" > wrote in message
...
>I was using Flight Following yesterday and was reminded of a problem that
>my RV has displayed for a long time: The transponder and altimeter do not
>agree. In general, ATC sees my altitude as about 200' lower than what is
>shown on my altimeter.
>
> A couple of facts:
>
> - The transponder/encoder always pass their certification checks.
>
> - The pitot/static system is installed per plans.
>
> Any thoughts?
>
> KB
>

[Kyle Boatright]

"Kyle Boatright" > wrote in message
...
>I was using Flight Following yesterday and was reminded of a problem that
>my RV has displayed for a long time: The transponder and altimeter do not
>agree. In general, ATC sees my altitude as about 200' lower than what is
>shown on my altimeter.
>
> A couple of facts:
>
> - The transponder/encoder always pass their certification checks.
>
> - The pitot/static system is installed per plans.
>
> Any thoughts?
>
> KB

An update on this thread... There are no apparent loose hoses, etc between
the altimeter and encoder which would explain a discrepancy between the two.
Also, the altimeter is 30' off (it reads low) on the ground which is well
within limits. This 30' low reading is consistent in flight (to the best of
my ability to gauge it during a low pass).

Presumably, this means the encoder needs to be adjusted. Other thoughts?

Oh, and by the way, climbing under the panel of an RV-6 to check this stuff
ain't no fun...

KB

[Dave[_16_]]

Kyle Boatright wrote:
> "Kyle Boatright" > wrote in message
> ...
>> I was using Flight Following yesterday and was reminded of a problem that
>> my RV has displayed for a long time: The transponder and altimeter do not
>> agree. In general, ATC sees my altitude as about 200' lower than what is
>> shown on my altimeter.
>>
>> A couple of facts:
>>
>> - The transponder/encoder always pass their certification checks.
>>
>> - The pitot/static system is installed per plans.
>>
>> Any thoughts?
>>
>> KB
>
> An update on this thread... There are no apparent loose hoses, etc between
> the altimeter and encoder which would explain a discrepancy between the two.
> Also, the altimeter is 30' off (it reads low) on the ground which is well
> within limits. This 30' low reading is consistent in flight (to the best of
> my ability to gauge it during a low pass).
>
> Presumably, this means the encoder needs to be adjusted. Other thoughts?
>
> Oh, and by the way, climbing under the panel of an RV-6 to check this stuff
> ain't no fun...
>
> KB
>
At a minimum you need to have your altimeter and encoder
correlated/adjusted by somebody rated to do that. In the mean time, turn
off the alt reporting at the transponder.
The adjustment can't be done without the proper equipment, sorry.
The next question is why did the encoder drift off by so much and will
it do it again? Since it's drifted that much, it might be worthwhile to
get a new encoder. They're pretty cheap.

The altimeter can only be legally adjusted by a certified repair
station. It's a good idea to make sure the altimeter is accurate when a
new encoder is installed.

Dave
www.craigmileaviation.com

[Rich S.[_1_]]

"Dave" > wrote in message
...
>
> The altimeter can only be legally adjusted by a certified repair station.
> It's a good idea to make sure the altimeter is accurate when a new encoder
> is installed.

Hmmm ........ Lessee. I'm just working off the cuff here, but if an
altimeter isn't even a required piece of equipment, why would the above
statement be true? In an experimental aircraft, couldn't I use a barometer
and a wet string if I wanted?

Rich (ducking and hiding) S.

[Ron Wanttaja]

On Sat, 11 Aug 2007 15:47:46 -0700, "Rich S." >
wrote:

>"Dave" > wrote in message
...
>>
>> The altimeter can only be legally adjusted by a certified repair station.
>> It's a good idea to make sure the altimeter is accurate when a new encoder
>> is installed.
>
>Hmmm ........ Lessee. I'm just working off the cuff here, but if an
>altimeter isn't even a required piece of equipment, why would the above
>statement be true? In an experimental aircraft, couldn't I use a barometer
>and a wet string if I wanted?

Actually, an altimeter *is* required for VFR. It's just that a "sensitive
altimeter adjustable for barometric pressure" isn't required unless you're going
IFR. That keeps all the one-armed Cub altimeters legal....

Ron Wanttaja

[Rich S.[_1_]]

"Ron Wanttaja" > wrote in message
...
>
> Actually, an altimeter *is* required for VFR. It's just that a "sensitive
> altimeter adjustable for barometric pressure" isn't required unless you're
> going
> IFR. That keeps all the one-armed Cub altimeters legal....

So the barometer and wet string is okay?

Rich :)

[Ron Wanttaja]

On Sat, 11 Aug 2007 17:36:27 -0700, "Rich S." >
wrote:

>"Ron Wanttaja" > wrote in message
...
>>
>> Actually, an altimeter *is* required for VFR. It's just that a "sensitive
>> altimeter adjustable for barometric pressure" isn't required unless you're
>> going
>> IFR. That keeps all the one-armed Cub altimeters legal....
>
>So the barometer and wet string is okay?

I kinda prefer orange-painted walnuts and a stopwatch, but yes... :-)

Ron Wanttaja

[Rich S.[_1_]]

"Ron Wanttaja" > wrote in message
...
>
> I kinda prefer orange-painted walnuts and a stopwatch, but yes... :-)

I went up with a fellow in his 200 hp. Musketeer once. He couldn't get
takeoff speed at Port Orchard with three of us aboard, so I gladly got out
and drove to Bremerton, where they picked me up. He said it was still tough
going to get above the trees at Port Orchard (2,600 paved with 1,000' from
the end of the runway to 150' tall trees).

As we were climbing out from Bremerton, I peered over his shoulder from the
back seat. He was climbing out at 80 mph and full throttle. The ROC
indicated 2,000 fpm. My watch indicated 300 fpm. He had a hard time
believing that he wasn't going up almost a half-mile a minute.

The next annual showed two jugs with compression below 50. Cost him a
bundle, but not as much as the last incident where he ran over his pickup
with the tail of the plane. I think he may part it out.

Rich S.

[Roger (K8RI)]

On Sun, 5 Aug 2007 12:40:36 -0400, "Kyle Boatright"
> wrote:

>I was using Flight Following yesterday and was reminded of a problem that my
>RV has displayed for a long time: The transponder and altimeter do not
>agree. In general, ATC sees my altitude as about 200' lower than what is
>shown on my altimeter.
>
>A couple of facts:
>
>- The transponder/encoder always pass their certification checks.
>
>- The pitot/static system is installed per plans.
>
>Any thoughts?

Try it at a controled airport. Get an altimeter check while
stationary. Make a low pass and get another to see how they vary.

>
>KB
>