Cambridge L-Nav audio vario just ate it...

On my last flight my audio vario suddenly started to read a consistent
300-400 fpm too high for the present conditions. I have a mechanical
vario that remained accurate and on my L-Nav screen my average fpm
sink rate was correct. Any ideas what I can check? It was really
annoying when I was sinking at a true 300 fpm on glides but my audio
was telling me I was going up 100fpm. If only it was always that way
in real life!

Thanks,
Bruno - B4

On Nov 13, 5:50*pm, Bruno wrote:
On my last flight my audio vario suddenly started to read a consistent
300-400 fpm too high for the present conditions. *I have a mechanical
vario that remained accurate and on my L-Nav screen my average fpm
sink rate was correct. *Any ideas what I can check? *It was really
annoying when I was sinking at a true 300 fpm on glides but my audio
was telling me I was going up 100fpm. *If only it was always that way
in real life! *

Thanks,
Bruno - B4

Hi Bruno,

What you wrote is a little confusing. I wonder if you meant that the
dial was showing high along with the audio tone, while the LNAV LCD
screen showed a believable average (and netto)? As you probably
know, it is possible to adjust the zero and gain on the vario through
the configure screen, and the manual tells you what the acceptable
zero number ranges are. It would at least be interesting to have a
look at those values and see what they show. But, it wouldn't
explain (at least to me) while the dial and audio are out of sync with
the other values.

Sounds like a trip to NK is in order.

P3

On Nov 13, 3:26*pm, Papa3 wrote:
On Nov 13, 5:50*pm, Bruno wrote:

On my last flight my audio vario suddenly started to read a consistent
300-400 fpm too high for the present conditions. *I have a mechanical
vario that remained accurate and on my L-Nav screen my average fpm
sink rate was correct. *Any ideas what I can check? *It was really
annoying when I was sinking at a true 300 fpm on glides but my audio
was telling me I was going up 100fpm. *If only it was always that way
in real life! *

Thanks,
Bruno - B4

Hi Bruno,

What you wrote is a little confusing. *I wonder if you meant that the
dial was showing high along with the audio tone, while the LNAV LCD
screen showed a believable average (and netto)? * *As you probably
know, it is possible to adjust the zero and gain on the vario through
the configure screen, and the manual tells you what the acceptable
zero number ranges are. * *It would at least be interesting to have a
look at those values and see what they show. * But, it wouldn't
explain (at least to me) while the dial and audio are out of sync with
the other values.

Sounds like a trip to NK is in order.

P3

That's interesting. I have an old Cambridge CAV series audio vario in
my Speed Astir. Every once in a great while, it will start to read
200-300 fpm climb when I'm NOT climbing. This usually happens several
hours into the flight, when I'm fairly tired of the annoying noises it
makes too much of the time anyhow. In its defense, it is probably just
trying to make up for the seemingly endless fields of sink that force
it to honestly inform me that I'm dropping like a frigging rock (and
have been for the last dozen miles). Perhaps it's just trying to cheer
me up?? I used to think maybe it was voltage related, when I was using
a 12v battery, but it does it even with my 14v setup.

On Nov 13, 4:26*pm, Papa3 wrote:
On Nov 13, 5:50*pm, Bruno wrote:

On my last flight my audio vario suddenly started to read a consistent
300-400 fpm too high for the present conditions. *I have a mechanical
vario that remained accurate and on my L-Nav screen my average fpm
sink rate was correct. *Any ideas what I can check? *It was really
annoying when I was sinking at a true 300 fpm on glides but my audio
was telling me I was going up 100fpm. *If only it was always that way
in real life! *

Thanks,
Bruno - B4

Hi Bruno,

What you wrote is a little confusing. *I wonder if you meant that the
dial was showing high along with the audio tone, while the LNAV LCD
screen showed a believable average (and netto)? * *As you probably
know, it is possible to adjust the zero and gain on the vario through
the configure screen, and the manual tells you what the acceptable
zero number ranges are. * *It would at least be interesting to have a
look at those values and see what they show. * But, it wouldn't
explain (at least to me) while the dial and audio are out of sync with
the other values.

Sounds like a trip to NK is in order.

P3

Sorry for being confusing in my description. It is exactly as you
state. I will take a look at those values. Good idea. I wonder why
it would go so out of adjustment when it always was working properly
before?

Thanks for the ideas,
Bruno -B4

Bruno wrote:
On Nov 13, 4:26 pm, Papa3 wrote:
On Nov 13, 5:50 pm, Bruno wrote:

On my last flight my audio vario suddenly started to read a consistent
300-400 fpm too high for the present conditions. I have a mechanical
vario that remained accurate and on my L-Nav screen my average fpm
sink rate was correct. Any ideas what I can check? It was really
annoying when I was sinking at a true 300 fpm on glides but my audio
was telling me I was going up 100fpm. If only it was always that way
in real life!
Thanks,
Bruno - B4
Hi Bruno,

What you wrote is a little confusing. I wonder if you meant that the
dial was showing high along with the audio tone, while the LNAV LCD
screen showed a believable average (and netto)? As you probably
know, it is possible to adjust the zero and gain on the vario through
the configure screen, and the manual tells you what the acceptable
zero number ranges are. It would at least be interesting to have a
look at those values and see what they show. But, it wouldn't
explain (at least to me) while the dial and audio are out of sync with
the other values.

Sounds like a trip to NK is in order.

P3

Sorry for being confusing in my description. It is exactly as you
state. I will take a look at those values. Good idea. I wonder why
it would go so out of adjustment when it always was working properly
before?

Thanks for the ideas,
Bruno -B4

Backup battery? All kinds of really weird stuff happens when they go
flat. Its a little internal coin sized battery. Easily replaced.

Or the sensor could have died, which means a trip to NK...

-Dave
ZL

I am betting with ZL. Data hold battery inside the L-Nav. I had one
that did that. Of course, on the first flight of a new to me plane,
so I had no idea what the varios were trying to tell me. Not that it
mattered, as there was no lift to speak of.

Steve
ZS

On Nov 13, 5:50*pm, Bruno wrote:
On my last flight my audio vario suddenly started to read a consistent
300-400 fpm too high for the present conditions. *I have a mechanical
vario that remained accurate and on my L-Nav screen my average fpm
sink rate was correct. *Any ideas what I can check? *It was really
annoying when I was sinking at a true 300 fpm on glides but my audio
was telling me I was going up 100fpm. *If only it was always that way
in real life! *

Thanks,
Bruno - B4

Look for internal leak on capacity side of fate of climb sensor.
Connected with tubing which gives up. TE suction causes flow through
sensor.
Good luck '
UH

Ah, yes, the "fate of climb" sensor. I've got a whole new respect for
"final glide", now.

-John

On Nov 15, 3:01 pm, wrote:
Look for internal leak on capacity side of fate of climb sensor.
Connected with tubing which gives up. TE suction causes flow through
sensor.
Good luck '
UH

I had a problem with my LNAV some years ago. Can't recall details but
might have been similar symptoms to yours and caused by a faulty G-
meter. Turns out (1) I had a spare G-meter because mine had acted up a
few years earlier; I had contacted CAI, and they sent me a new one
that I never installed because the problem went away; and (2) I was
flying a regional at Sugarbush, VT, HQ of CAI at the time! Dave Ellis
himself came over after I landed and installed the new G-meter and
returned the software offsets the proper values (I had changed them in
the air that day in an attempt to "fix" the problem). He also wired up
my old Magellan handheld GPS (this was many years ago) so I had
automatic wind for the first time.

If you're into tinkering, I suppose you could remove the G-meter (it
just plugs in) to see if that makes the problem go away. I don't have
the manual in front of me but you might have to reconfigure the
instrument to work properly. Anyone have a thought on this?

Chip Bearden
ASW 24 "JB"
USA

On Nov 18, 2:32*pm, Chip Bearden wrote:
I had a problem with my LNAV some years ago. Can't recall details but
might have been similar symptoms to yours and caused by a faulty G-
meter. Turns out (1) I had a spare G-meter because mine had acted up a
few years earlier; I had contacted CAI, and they sent me a new one
that I never installed because the problem went away; and (2) I was
flying a regional at Sugarbush, VT, HQ of CAI at the time! Dave Ellis
himself came over after I landed and installed the new G-meter and
returned the software offsets the proper values (I had changed them in
the air that day in an attempt to "fix" the problem). He also wired up
my old Magellan handheld GPS (this was many years ago) so I had
automatic wind for the first time.

If you're into tinkering, I suppose you could remove the G-meter (it
just plugs in) to see if that makes the problem go away. I don't have
the manual in front of me but you might have to reconfigure the
instrument to work properly. Anyone have a thought on this?

Chip Bearden
ASW 24 "JB"
USA

You have to install a jumper across a couple pins when G meter is
removed.
Did once with help from ex Cambridge guy. Gary K at NK would know this
ine.
UH