Pitot/Static/Transponder Problem

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

"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.

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

"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

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

"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.

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