Avidyne Homepage
Forum Home Forum Home > Avidyne General > IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
  New Posts New Posts RSS Feed - Acceptable altitude input for FPL leg sequencing
  FAQ FAQ  Forum Search   Register Register  Login Login

Acceptable altitude input for FPL leg sequencing

 Post Reply Post Reply
Author
Message
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Topic: Acceptable altitude input for FPL leg sequencing
    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?

Vince
Back to Top
skitheo View Drop Down
Groupie
Groupie
Avatar

Joined: 02 Jan 2016
Location: 3S8
Status: Offline
Points: 62
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.
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
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.
Vince
Back to Top
Catani View Drop Down
Senior Member
Senior Member


Joined: 21 Jan 2016
Status: Offline
Points: 180
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.
Back to Top
ddgates View Drop Down
Senior Member
Senior Member
Avatar

Joined: 12 Aug 2011
Location: Deer Valley
Status: Offline
Points: 917
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.
David Gates
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
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.



Vince
Back to Top
AviSimpson View Drop Down
Senior Member
Senior Member


Joined: 31 Mar 2015
Location: Lincoln, MA
Status: Offline
Points: 760
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
Avidyne Corporation
Product Manager
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
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?


Vince
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
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
Vince
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
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?

Vince
Back to Top
AviSimpson View Drop Down
Senior Member
Senior Member


Joined: 31 Mar 2015
Location: Lincoln, MA
Status: Offline
Points: 760
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
Avidyne Corporation
Product Manager
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 2018 at 2:40pm
I would like to raise this question again now that new Avidyne "faces" have come on the scene. Perhaps this is one where AviSteve could add some enlightenment.

I guess I need to accept Simpson's statement that the IM manual quote above is an error, although I have not seen any correction unless there is a new manual version yet unknown to me.

However, I find the justification for needing external baro-alt input in order to auto-sequence a Heading to Altitude leg (most common on a missed approach) less than satisfying per Simpson's 2nd comment that "The Heading to Altitude legs are defined in the database as MSL altitudes, therefore the IFD requires baro-corrected altitude to properly sequence".

The IFD's use GPS altitude for all RNAV/RNP approach DA when auto-sequencing to the missed approach, or am I mistaken? When reading IAC's, these look like MSL not GPS altitudes, or are they instead "defined as GPS altitudes in the database"?

Having to manually sequence right at the beginning of a missed approach is not critical but certainly an additional workload subject to being "missed" ;-) during a distraction.

Clearly this is a non-issue for all those with Aspens or other ADC's, but it is an expensive criteria to meet for those without.

Is there a regulatory/certification/compliance issue preventing Avidyne from using GPS altitude to auto-sequence in this case?
Vince
Back to Top
AviSteve View Drop Down
Admin Group
Admin Group
Avatar

Joined: 12 Feb 2018
Location: Melbourne, FL
Status: Offline
Points: 152
Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 2018 at 10:02pm

You're right that the IFDs use GPS altitude for the final approach segment of SBAS approaches, but the final approach segment is inherently GPS based.  Think of the final approach segment as you would an ILS beam.  Guidance is provided to the beam, not the legs you see on the flight plan.  Also, The FMS doesn't use DA to determine when to go missed.  It only activates the first leg of the missed approach by crossing the missed approach point - a lateral measurement - just like any other fix terminated leg. Once you're on the missed, you are off of the final approach segment and back on leg-based guidance.  Altitude terminated legs are *always* climb legs, so you'll never see them on the front side of an approach; only the missed. 

Simpson was correct that altitude terminated legs are defined using an MSL reference.  While we can estimate MSL using GPS altitude and a geoid model, we just don't feel comfortable sequencing an altitude terminated leg based on that estimate.  This is especially true of the first leg of a missed approach, which typically takes you to 400 AGL to get you clear of obstructions around the airport.  The last thing we would want to do is sequence early, indicate that it's OK to turn, and then direct someone fly into an obstruction.  I can't say that I know of a regulation saying "thou shalt use only baro altitude" to sequence an altitude terminated leg, but from a safety perspective, we don't feel comfortable using anything else.

I wish we had a more convenient way for you to manually sequence the leg, but there just isn't the real estate available.  On R9 systems, we had a dedicated button for this kind of thing on the PFD.  Of course, in that system, this particular issue wasn't a problem since we have an ADC.  Nevertheless, on the IFDs we had limited choices and the best of those choices was to overload the button on the plan page.

Steve Lindsley
Avidyne Engineering
Back to Top
chflyer View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Jan 2013
Location: LSZK
Status: Offline
Points: 531
Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb 2018 at 3:57am
Thanks for the additional info and your basis for the requirement.

On further reflection, I realised that the MAP on a precision approach with DA is a position in space / geographic location which one can identify via GPS data as being passed. The end of a Heading to Altitude leg is not a defined location, since it depends on the rate of climb. As such, only altitude data, whatever acceptable source that may have, is available to identify the end of the leg.
Vince
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.049 seconds.