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Acceptable altitude input for FPL leg sequencing

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chflyer View Drop Down
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    Posted: 31 Aug 2017 at 6:25pm
In the IFD540 PG, page 5-4, there is a NOTE box at the top of the page which says the following:
"In Electro-mechanical installations where the IFD does not have an altitude input, a CAS message ("Manual Sequence Req'd") prompting the pilot to manually sequence legs of the flight plan will be presented on Heading-to-Altitude legs."

Does anyone know what exactly qualifies as "altitude input" in this specific context?

For example, in the IM section 7.5.3 there is an RS-232 channel input selection called "Icarus-alt", applicable to serial altitude data from a Sandia SAE 5-35 amongst other devices. Would this meet the altitude input requirement for automatic sequencing on Heading-to-Altitude legs?

Simpson?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote skitheo Quote  Post ReplyReply Direct Link To This Post Posted: 02 Sep 2017 at 12:56am
I've had the same question. I would expect that it's air data, but for a missed approach point or procedure leg, it would require baro-compensated altitude data. I.e. from an Aspen, G-5, Skyview HDX, G500, etc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 02 Sep 2017 at 1:20am
I suspect that you're right, but I can't find a clear statement on this anywhere.

There was a comment from Avidyne in a thread a long time ago that at from release x.xx GPS altitude would be accepted but I can't find it anymore and suspect it has been removed.

It would be a shame if this needs air data. If one doesn't already have an Aspen or altimeter with baro output, I can't find any way of getting air data for less than >$5'000 if everything is added together. A large piece of cash just to get auto-sequencing for these legs.... hardly worth it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Catani Quote  Post ReplyReply Direct Link To This Post Posted: 02 Sep 2017 at 12:08pm
The IFD accepts baro-altitude from Avidyne's EX5000 PFD, among others - none of which are free.  I'm not sure how the IFD would know when to sequence if it had no baro-corrected altitude input to substitute for the pilot's eyeballing the baro-corrected altimeter on the panel (or PFD) - the traditional source for altitude data the charts are based upon.  For reasons not clear to me, GPS altitude often differs from baro-altitude, a discrepancy that may make relying upon GPS instead of an altimeter an unacceptable alternative, at least from a legal standpoint.  Which, of course, would explain why the IFD cannot use GPS as an alternative, until such time as TERPS declares it acceptable - which it may have already done for all I know.  I assume that is not the case until advised otherwise.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddgates Quote  Post ReplyReply Direct Link To This Post Posted: 02 Sep 2017 at 12:16pm
Per AviJake, effective with 10.1.0.0, the IFD accepts GPSalt for advisory GS (and I think also for 500 AGL callout), but I think baro correction is required for other VNAV related functions, such as this one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep 2017 at 2:34am
Exactly. A table would be useful with the various situations when altitude is used/applied by the IFD along with an indication for each of whether gps or baro-alt or either is the reference.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSimpson Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 2017 at 11:10am

The Heading to Altitude legs are defined in the database as MSL altitudes, therefore the IFD requires baro-corrected altitude to properly sequence.

Reading the available information on the SAE 5-35 Altitude Encoder, I don’t believe it will suffice. Per the Sandia Installation Manual:

The data output of the SAE5-35 is referenced to 29.92 inch HG (1013 Millibars). The SAE5-35 has been designed to provide altitude data to GPS and Terrain Awareness Systems in addition to Mode C Transponders.

It doesn’t appear there is a way to enter or apply a local barometric correction to the output of the SAE 5-35 and therefore it is not sufficient for those leg types.

Another Sandia airdata computer that does support baro-corrected altitude reporting is the SAC 7-35, though it is quite a bit more expensive ($2795 vs $450). Per the 7-35 IM:

If the aircraft has an altimeter with a 5 VDC baro pot, the SAC 7-35 can use this to provide corrected altitude output on the ARINC 429 bus. The Garmin-Z output format does not support Baro Correction information. But, when the baro input is available the data will be included in the King-D and Garmin-G serial RS-232 airdata outputs.

Simpson Bennett
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2017 at 4:12pm
So if there isn't already an altimeter with baro output and ADC or an Aspen, then this is a $5k+ hit just to get automatic sequencing..... a bit steep and doesn't pass cost/benefit analysis.

Why can't the IFD use the manually set BARO field of its own Air Data Calculator?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 12 Nov 2017 at 6:01pm
I believe that there is an error in the IM manual related to this subject.

The IFD5xx/4xx IM 600-00299-000 rev 10 (i.e. for software rel 10.2), says the following in section 2.4.2 IFR Installation (bullet 6) on page 43 ...
"IFD5XX/4XX should be interfaced to an Airdata source for automatic altitude leg sequencing (optional). If no baro-altitude data is supplied, altitude leg types must be manually sequenced for IFD5XX with Software 10.0.3.0 or earlier."
(bold is my emphasis)

I interpret this to mean that the IFD5XX can automatically sequence altitude leg types without baro-altitude data input for releases after 10.0.3.0.

I'm currently running 10.1.3 (without baro-altitude input) and I still need to manually sequence.

Is anyone running 10.2 without baro-altitude input who can indicate if automatic sequencing of altitude leg types is now supported or not?

I find manually sequencing during a missed approach to be a pain, but I'm not ready to spend >$5k just to get auto-sequencing.


Edited by chflyer - 12 Nov 2017 at 6:06pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 12 Nov 2017 at 6:10pm
Another question arising from your reply, Simpson ...

"If the aircraft has an altimeter with a 5 VDC baro pot, the SAC 7-35 can use this to provide corrected altitude output on the ARINC 429 bus. The Garmin-Z output format does not support Baro Correction information. But, when the baro input is available the data will be included in the King-D and Garmin-G serial RS-232 airdata outputs."

Does the IFD540 require the baro-altitude to be presented via the ARINC 420 bus, or will it also accept baro-altitude on a Garmin-G serial RS-232 input?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSimpson Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2017 at 9:33am
Originally posted by chflyer chflyer wrote:

I believe that there is an error in the IM manual related to this subject.

The IFD5xx/4xx IM 600-00299-000 rev 10 (i.e. for software rel 10.2), says the following in section 2.4.2 IFR Installation (bullet 6) on page 43 ...
"IFD5XX/4XX should be interfaced to an Airdata source for automatic altitude leg sequencing (optional). If no baro-altitude data is supplied, altitude leg types must be manually sequenced for IFD5XX with Software 10.0.3.0 or earlier."
(bold is my emphasis)

I interpret this to mean that the IFD5XX can automatically sequence altitude leg types without baro-altitude data input for releases after 10.0.3.0.

I'm currently running 10.1.3 (without baro-altitude input) and I still need to manually sequence.

Is anyone running 10.2 without baro-altitude input who can indicate if automatic sequencing of altitude leg types is now supported or not?

I find manually sequencing during a missed approach to be a pain, but I'm not ready to spend >$5k just to get auto-sequencing.

I believe you are right, this is an error in the IM. The FMS will only sequence altitude terminated legs if it has a valid baro altitude input. This has remained unchanged since 10.0.

Simpson Bennett
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