IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM - Feature Request

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Feature Request - ICAO Cold Temperture Corrections

Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=495
Printed Date: 12 Mar 2025 at 1:32pm
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com

Topic: Feature Request - ICAO Cold Temperture Corrections

Posted By: roltman
Subject: Feature Request - ICAO Cold Temperture Corrections
Date Posted: 13 Dec 2014 at 4:54pm

With the 272 new airports in the US implementing cold Wx limitations beginning January 8, 2015 what's the chance the ICAO table can be built in to the IFD540 and some automation in correcting for it?

Something similar to, but possibly better than, what the G450 does in this example would be nice?
http://code7700.com/altimeter_temperature_correction.html

Replies:

Posted By: AviJake
Date Posted: 14 Dec 2014 at 9:52am

I don't have any idea what this is right now.

And are you asking for a pdf table kind of thing or something else?

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Steve Jacobson
sjacobson@avidyne.com

Posted By: roltman
Date Posted: 14 Dec 2014 at 11:41am

I guess it would be an option for a user to enter a field temperature and enable ICAO adjusted approach altitudes. It looks like Honeywell/Gulfstream allow the entry all the time, but if one of the airports where loaded in the IFD540 that required it then it'd present a field to the user where they could enter the reported field temperature and get alternate minimums in the flight plan if the criteria were met.

EASA has had these conversions requirements for a few years. The FAA is adopting them, and 272 airports beginning in the first cycle of 2015 will have cold temperature limitations applied to them.

Page 446 of http://www.faa.gov/air_traffic/publications/notices/media/12-11-14_NTAP.pdf explains it.

I do believe Jepp knows about which segments and/or airports have these limitations; however, if the limitation applies due to cold surface temperatures at the airport, the pilot now must compute new minimums based on the ICAO table and use the adjusted alternate minimum altitude. To me this is a lot of juggling particularly since the temperatures at which they apply can be as high as 0C down to -60C depending on the airport.

For example KRUT in Vermont has a limitation at only -4C or 25F which I think it'd hit somewhat regularly in the winter months.

Further details can be found in ICAO 8168 Vol 1 chapter 4.3 along with a copy of the formula in section 4.3.4. This formula comes from Engineering Sciences Data Unit (ESDU)'s publication called: "Performance", Volume 2, Item number 77022 for off-standard temperature atmosphere.

I couldn't find a direct ICAO link for the aforementioned document, but here's another website's copy:
http://code7700.com/pdfs/icao_doc_8168_vol_1.pdf
See page 233 of 279 for the formula that could be implemented in the FMS.

Since EASA and FAA have adopted this, I figured it'd be a nice feature to help offload some work from the pilots around the world who hit these colder climates.

Posted By: oskrypuch
Date Posted: 14 Dec 2014 at 11:58am

In Canada this is required at every airport, if the temps are low enough.

Well, it would be cool to have included in the 540, but there is a much faster way to correct the altitudes than consulting the ICAO table.

At 0C - adjust the minimums height above the ground value by 5%. For example, if FAF minimum is 1600ft MSL, and ground elevation is 600ft MSL, increase the 1600ft minimum by (1600-600) * 5% = 50 ft, so new FAF minimum is 1650ft MSL.

At -10C adjust by 10%

At -15C adjust by 15%

At -20c adjust by 20%

It is remarkably close to the table values.

* Orest

Posted By: roltman
Date Posted: 14 Dec 2014 at 12:03pm

Unfortunately the way I interpret the FAA's implementation you'd have to know at what temperature it applies first. The FAA merely took the coldest temp X-years prior and determined if the approach still met the TERPs. If not then it was flagged and the temperature where it failed the TERPs became the temperature where the conversion was applied.

I guess nothing would prevent a person from always applying the cold Wx minimums, but seemed like a good feature putting all those Jepp $$$s to work for us. :)

Posted By: AviJake
Date Posted: 14 Dec 2014 at 12:26pm

Okay, we'll look into it. In any case, I just entered the idea into our future feature candidate database.

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Steve Jacobson
sjacobson@avidyne.com

Posted By: AviJake
Date Posted: 20 Jul 2015 at 12:27pm

We started trying to implement this in the next release until we looked at each other like a couple of ding dongs so maybe you can help clarify the intent of this one.

If I understand it correctly, we're talking about altering published minimums for an approach due to cold temperatures.

Presuming that is true, the issue with the IFD540 and 440 wrt this topic is since the 540/440 don't support any notion of approach minimums, there is nothing to apply these corrections to. So we don't have anything to do wrt this topic. Anyone see it differently?

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Steve Jacobson
sjacobson@avidyne.com

Posted By: oskrypuch
Date Posted: 21 Jul 2015 at 12:41am

It is not just the final DA or MDA that is adjusted, it is the FAF crossing height, procedure turn altitude, feeder legs minimums, etc.

* Orest

Posted By: AviJake
Date Posted: 21 Jul 2015 at 5:37am

Sure but the 540/440 uses GPS-based altitude for FMS operations and not baro-based altitude so I still don't know of anything to correct. An EFIS/PFD would be a different story obviously but the 540/440 is unaffected.

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Steve Jacobson
sjacobson@avidyne.com

Posted By: oskrypuch
Date Posted: 21 Jul 2015 at 8:21am

Personally, I would not put much priority on this feature, as I mention up thread it is pretty easy to correct on the fly yourself.

Let's get that Boeing banana, and/or FIX page done! Both unique (to GA) AND extremely powerful and operationally useful items!

* Orest

Posted By: wsh
Date Posted: 31 Mar 2021 at 3:55am

I stumbled on this post. Was this feature ever implemented?

Posted By: chflyer
Date Posted: 31 Mar 2021 at 9:23am

Orest, can you remind me/us what the FIX page request was?

Been enjoying the banana since it was implemented. Thanks for bringing that idea, which was previously less known to the GA community.

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Vince

Posted By: AviSteve
Date Posted: 31 Mar 2021 at 11:04am

No, it hasn't been implemented. Here's a http://forums.avidyne.com/feature-request-what-about-a-fix-page_topic243_post956.html" rel="nofollow - link to Orest's original post .

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Steve Lindsley
Avidyne Engineering

Posted By: oskrypuch
Date Posted: 02 Apr 2021 at 6:10pm

Thanks AviSteve for the link.

I called it a FIX page, for the name that Boeing calls that particular page in the FMS.

You define up to three (or ten in later updates) points, and then can define up to four radials/circles to be drawn on the ND relative to these points. For example your could draw in a 10nm and 20nm circle around the destination airport, with an inbound radial orientated to the runway. You could draw it around areas you want to avoid. Very handy for ETOPS planning, but not in a SE prop!

An outstanding too for quick visual orientation, and would be unique in GA units.

And, YES, we all love the banana!

* Orest

Posted By: carlsonj
Date Posted: 03 Jan 2022 at 3:23pm

For what it's worth (and in order to clarify the request a bit), the equivalent feature on the GTN750 does two things:

- Adjusts initial, intermediate, and missed altitudes displayed to the user as required

- Appends a "snowflake" symbol after the altitude so the pilot knows they've been adjusted.

I definitely understand that the computed GPS altitude is unaffected by temperature. That's not really the issue. The issue is that the displayed minimum altitudes for approach procedures are *indicated* altitudes that we have to fly with reference to our altimeters, and *not* something that we can legally fly using a GPS altitude. And those indicated altitudes have to change when it's cold.

So, yeah, the issue about the lines of minima needing adjustment as well (and neither Garmin nor Avidyne display those altitudes, so there'd be nothing to adjust) is well-taken, but not complete.

And, no, it obviously doesn't affect something like a computed glideslope, which is purely a GPS reference.

A possible alternative for the feature (though a little more error-prone and distracting) would be to have a new section under "Calculators" that given OAT, field elevation, and segment altitude gives the ICAO adjustment value. But the GTN presentation is already known to (at least some) pilots.

Posted By: bikermd
Date Posted: 08 Feb 2025 at 3:59pm

I know that its been some time since there has been posting on this topic, would it be possible to at least give us a calculator where we could put in our altitude and the current temp (either F or C) and get the correction altitude we need to add for cold weather approaches?

Posted By: chflyer
Date Posted: 08 Feb 2025 at 4:09pm

Even better if the calculator would automatically populate the altitude and temp if available, similar to the air data calculator. In fact, there may well be room for this as an additional field on the existing air data calculator.

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Vince