Altitude Encoder w/ GPS Question

[Scott Rodriguez]

Looking at buying an altitude encoder for the transponder in my
yet-to-be-born homebuilt.

I see some altitude encoders have an RS-232 output for sending altitude
information to a GPS. What kind of functionality does this provide? Is it
"real-world" useful?

Thanks!

Scott

[Ron Natalie]

Scott Rodriguez wrote:
> Looking at buying an altitude encoder for the transponder in my
> yet-to-be-born homebuilt.
>
> I see some altitude encoders have an RS-232 output for sending altitude
> information to a GPS. What kind of functionality does this provide? Is it
> "real-world" useful?
>
It's required for IFR approach certification I believe. I'd suspect
that the MX20 also uses it for the terrain warning feature because it
asks me for the altimeter setting periodically as well (which only
would be useful if it was looking at a pressure alt somewhere).

[Dave S]

Ron Natalie wrote:
> Scott Rodriguez wrote:
>
>> Looking at buying an altitude encoder for the transponder in my
>> yet-to-be-born homebuilt.
>>
>> I see some altitude encoders have an RS-232 output for sending altitude
>> information to a GPS. What kind of functionality does this provide?
>> Is it
>> "real-world" useful?
>>
> It's required for IFR approach certification I believe.

Negative. The encoder can be used to provide altitude alerting functions
through the gps, but it's not precise enough for providing vertical
guidance in an approach. The typical serial encoder reports in 100 ft
increments.

Baro-vnav (which is not required to utilize an otherwise approach
certified GPS) requires a much more precise input signal.

My KLB 89B allows the connection of an encoder to it. It's sole
usefulness is in serving as an altitude alert, and in calculating
density altitude/true airspeed (not having to enter pressure altitude
manually)

Dave

[Jim Burns]

Our KLN94 is the same. Best thing the encoder can be used for in our unit
is to cancel the "Altitude Fail" message that pops up requiring you to
cancel it.
Jim

"Dave S" > wrote in message
ink.net...
> Ron Natalie wrote:
>> Scott Rodriguez wrote:
>>
>>> Looking at buying an altitude encoder for the transponder in my
>>> yet-to-be-born homebuilt.
>>>
>>> I see some altitude encoders have an RS-232 output for sending altitude
>>> information to a GPS. What kind of functionality does this provide? Is
>>> it
>>> "real-world" useful?
>>>
>> It's required for IFR approach certification I believe.
>
> Negative. The encoder can be used to provide altitude alerting functions
> through the gps, but it's not precise enough for providing vertical
> guidance in an approach. The typical serial encoder reports in 100 ft
> increments.
>
> Baro-vnav (which is not required to utilize an otherwise approach
> certified GPS) requires a much more precise input signal.
>
> My KLB 89B allows the connection of an encoder to it. It's sole usefulness
> is in serving as an altitude alert, and in calculating density
> altitude/true airspeed (not having to enter pressure altitude manually)
>
> Dave
>
>

[Ron Natalie]

Dave S wrote:
> Ron Natalie wrote:
>> Scott Rodriguez wrote:
>>
>>> Looking at buying an altitude encoder for the transponder in my
>>> yet-to-be-born homebuilt.
>>>
>>> I see some altitude encoders have an RS-232 output for sending altitude
>>> information to a GPS. What kind of functionality does this provide?
>>> Is it
>>> "real-world" useful?
>>>
>> It's required for IFR approach certification I believe.
>
> Negative. The encoder can be used to provide altitude alerting functions
> through the gps, but it's not precise enough for providing vertical
> guidance in an approach. The typical serial encoder reports in 100 ft
> increments.
>
Did I say SQUAT about vertical guidance. It is a requirement for
TSO-C129a CERTIFICATION. I didn't say what it was used for.
My statement appears to still hold true.

[Dave S]

Ron Natalie wrote:

>>
> Did I say SQUAT about vertical guidance. It is a requirement for
> TSO-C129a CERTIFICATION. I didn't say what it was used for.
> My statement appears to still hold true.

ARRGGGHHH!!!..

You are ABSOLUTELY CORRECT. The altitude source must be connected in
order to have an IFR certified installation. It even states as such in
my King KLN-89B installation manual. I missed those 2 sentences previously.

The irony of it is, I've got the wires installed for it on mine, even
though the only discernable function is the altitude alert, which I'm
not sure I'm going to use.

Thanks Ron.. I was wrong and you were right.

[Gerry Caron]

"Dave S" > wrote in message
ink.net...
> Ron Natalie wrote:
>
>>>
>> Did I say SQUAT about vertical guidance. It is a requirement for
>> TSO-C129a CERTIFICATION. I didn't say what it was used for.
>> My statement appears to still hold true.
>
> ARRGGGHHH!!!..
>
> You are ABSOLUTELY CORRECT. The altitude source must be connected in order
> to have an IFR certified installation. It even states as such in my King
> KLN-89B installation manual. I missed those 2 sentences previously.
>
> The irony of it is, I've got the wires installed for it on mine, even
> though the only discernable function is the altitude alert, which I'm not
> sure I'm going to use.
>
> Thanks Ron.. I was wrong and you were right.

The RAIM algorithm in the GPS needs the BARO input. It's only required use
is to support the integrity monitor. The altitude alert is a 'feature' that
King added for marketing (value-added) reasons. It cost them almost nothing
per unit and just a few thousand $ of non-recurring costs to develop the
software.

Gerry