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Driver170

Cold weather altimeter correction

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When flying in extreme cold conditions and correcting STAR altitudes. Does one apply the correction for Final Approach Fix altitudes also?

 

Is this necessary for FSX?

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Not sure what you are getting at here. The only thing that you change on the altimeter is the QNH when you are flying below transition level. That is related to barometric pressure, not temperature.

 

As far as STAR and FAF altitudes, you fly them as they are published.

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Absolutely a fact that cold temperatures affect the altimeter as all pressure instruments are calibrated to ISA. 

 

Realworld we have to take this into consideration. Low temps = lower than indicated.

 

Not sure if FSX models this though.

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Yes thats right meaning in higher altitude correction! But also not sure if fsx models this....

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But also not sure if fsx models this....

 

Well, I guess we can test it  ^_^

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Yes, very true.

 

Unfortunately, useless to get worried about it in MSFS or even X-Plane, or most of the simulators I know about. These sims do not model Geopotential height!

 

The well known: "from high to low, watch out bellow..." applies to both pressures and temperatures, because the colder air, being denser, also corresponds to a lower geopotential.

 

As far as I know  the ** only ** flight simulator that will, for the first time, model this effect, so common and realistic IRL, is Aerowinx PSX, about to be released - the 747-400 simulator. Hardy Heinlin, the Master of the 744 simulations, took even this into consideration in PSX's weather model  !!! 

 

BTW, and although it's not the same thing being asked in the OP, here's also a simple calculator for Air Density

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Hi,

 

we can do this in ASN if you like (we actually have taken control of ambient pressure, so we could calculate the ambient air density at the aircraft level based on real temperatures. We didn't, because we didn't want to risk making things too realistic for the average simmer).

 

BTW, Jose (jcomm) I don't remember you asking anything related in the 8+ months you participated in ASN beta testing :)

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we can do this in ASN if you like (we actually have taken control of ambient pressure, so we could calculate the ambient air density at the aircraft level based on real temperatures. We didn't, because we didn't want to risk making things too realistic for the average simmer).

 

DO it!  An option would be cool.

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Hi,

 

we can do this in ASN if you like (we actually have taken control of ambient pressure, so we could calculate the ambient air density at the aircraft level based on real temperatures. We didn't, because we didn't want to risk making things too realistic for the average simmer).

 

BTW, Jose (jcomm) I don't remember you asking anything related in the 8+ months you participated in ASN beta testing :)

 

 

Kostas,

 

I was referring to default FSX, not FSX with ASN :-)

And I did mention it as a wanted feature. I guess it was even considered for future work. Would be great to have!

 

Curiously, I suggested the same to Austin, for XP10, but he was too busy... Asked me to remind him again later :-) I will!

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I don't think most airlines worry about cold weather corrections until it's -25C or colder.

 

One airline I worked for started corrections at 0C.

 

It's a pain in the butt. For the small corrections starting at 0C, you're more likely to introduce an error than to fix one.

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I don't think most airlines worry about cold weather corrections until it's -25C or colder.

 

One airline I worked for started corrections at 0C.

 

It's a pain in the butt. For the small corrections starting at 0C, you're more likely to introduce an error than to fix one.

 

 

Exactly, I think if most people knew the hassle involved they would keep the feature switched off.  

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OK, I'll add it to our todo list (low priority and as an option only). Let's see how this works... 

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Hi,

 

we can do this in ASN if you like (we actually have taken control of ambient pressure, so we could calculate the ambient air density at the aircraft level based on real temperatures. We didn't, because we didn't want to risk making things too realistic for the average simmer).

 

BTW, Jose (jcomm) I don't remember you asking anything related in the 8+ months you participated in ASN beta testing :)

I would like to see that :)

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e didn't, because we didn't want to risk making things too realistic for the average simmer

 

Oh Lawd.

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FCOM -

 

Cold Temperature Altitude Corrections

Extremely low temperatures create significant altimeter errors and greater potential for reduced terrain clearance. When the temperature is colder than ISA, true altitude will be lower than indicated altitude.

The following altitude correction procedures should be considered when operating at or near airports where high terrain and/or obstacles exist in combination with very cold temperatures (-30°C or colder), or when en route minimum altitudes are affected by terrain clearance:

• no corrections are required for reported temperatures above 0°C

• corrections apply to QNH and QFE operations

• pilots should not correct altimeter barometric reference settings

• ATC assigned altitudes or flight levels should not be adjusted for

temperature

• apply corrections to all published minimum departure, en route and

approach altitudes, including missed approach altitudes, according to the table below. Advise ATC of the corrections

• MDA/DA settings should be set at the corrected minimum altitudes for the approach

• subtract the elevation of the altimeter barometric reference setting source (normally the departure or destination airport elevation) from the published minimum altitude to be flown to determine “height above altimeter source”

• enter the table with Airport Temperature and with “height above altimeter source”. Read the correction where these two entries intersect. Add the correction to the published minimum altitude to be flown to determine the corrected indicated altitude to be flown. To correct an altitude above the altitude in the last column, use linear extrapolation (e.g., to correct 6000 feet or 1800 meters, use twice the correction for 3000 feet or 900 meters, respectively)

• if the corrected indicated altitude to be flown is between 100 foot increments, set the MCP altitude to the closest 100 foot increment above the corrected indicated altitude to be flown.

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FCOM -

 

Cold Temperature Altitude Corrections

Extremely low temperatures create significant altimeter errors and greater potential for reduced terrain clearance. When the temperature is colder than ISA, true altitude will be lower than indicated altitude.

The following altitude correction procedures should be considered when operating at or near airports where high terrain and/or obstacles exist in combination with very cold temperatures (-30°C or colder), or when en route minimum altitudes are affected by terrain clearance:

• no corrections are required for reported temperatures above 0°C

• corrections apply to QNH and QFE operations

• pilots should not correct altimeter barometric reference settings

• ATC assigned altitudes or flight levels should not be adjusted for

temperature

• apply corrections to all published minimum departure, en route and

approach altitudes, including missed approach altitudes, according to the table below. Advise ATC of the corrections

• MDA/DA settings should be set at the corrected minimum altitudes for the approach

• subtract the elevation of the altimeter barometric reference setting source (normally the departure or destination airport elevation) from the published minimum altitude to be flown to determine “height above altimeter source”

• enter the table with Airport Temperature and with “height above altimeter source”. Read the correction where these two entries intersect. Add the correction to the published minimum altitude to be flown to determine the corrected indicated altitude to be flown. To correct an altitude above the altitude in the last column, use linear extrapolation (e.g., to correct 6000 feet or 1800 meters, use twice the correction for 3000 feet or 900 meters, respectively)

• if the corrected indicated altitude to be flown is between 100 foot increments, set the MCP altitude to the closest 100 foot increment above the corrected indicated altitude to be flown.

Clear as mud? It's a pain in the &@($*. You might as well get excited about having geriatric flight attendants or "service dogs" crapping themselves in the aisle.

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The level of complexity of PMDG models, and the level of weather simulation provided by ASN are, in many aspects, not noticed by many of us simmers, or we simply do not use all of those features, although we like to know we have it simulated.

 

Flight simulation, like probably many other hobbies, is just like that - we wan't  to have it all, even if we need far from that in hour ludic activities.

 

Anyway, this particular factor has some impact for precision approaches into airports under severe cold weather, and mountain pilots also know that "mountains are higher in the winter" specially when operating near the limits of their aircraft to clear their tops.

 

As a beta tester for ASN, and I think I should say this here because my initial reply might ( even if erroneously ) suggest I was referring to any specific weather modeling applications, I've seen aspects of weather being modeled and fine tuned in ASN like most of the time we will actually never even really be aware of. Modeling this particular feature will certainly present no problem to the HiFiTech team :-) 

 

I should also add that while some of you have probably read a few posts from me regarding Aerowinx PSX 744 simulator, and indeed, jut like Robert Randazzo, I think of Hardy Heinlin as a Genius! and I smile when I read the random pages from the manual of that sim and think of the sophistication and level of detail he, again, went into. It is that capacity that I admire, although it is out of question for me to pay such an amount for a flight simulator because I am not young nor a professional pilot, and certainly no longer someone that can dream of becoming an airline pilot ( my all life dream ), but, at the same time, when I look at the sophistication of PMDG products, and I got in the last two years the NGX and the 777, I think that - you guys do "miracles"! - because indeed, while not being so wide the coverage of the simulation ( you can build on a platform - FSX, and in sinergy with other great add-ons like ASN for the weather modeling... ) the level of detail and systems simulation, and the harmony of "flying" one of these simulated Boeings is more than enough to give us the sensation of being there, for a price that is actually, if we think about it, inexpensive!

 

I should add that while PMDG was already very very high on my consideration regarding the quality of their products, the way they run their business, the user support, the way they embraced that embarrassing situation with the Boeing FBW ( C*U law ) "problem" is simply REMARKABLE, and as a user, I am ready to welcome whatever the modifications made possible to implement are, and sure they'll certainly put, again, this product into the very top of 777 simulation for FSX / P3D, and actually X-Plane 10 too, specially because there are aspects that I am sure they will never be able to get access to / even less be allowed to port into a public use flight simulation platform /game.

 

Sorry for the long post :-/

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The only time temperature correction comes into play for us is when we are doing RNAV approaches.  If the temperature is hotter or colder than the published VNAV temperature limitations we can't do the approach, period.

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The only time temperature correction comes into play for us is when we are doing RNAV approaches.  If the temperature is hotter or colder than the published VNAV temperature limitations we can't do the approach, period.

 

Ok, but if in the sim you could get the effects modeled, it would be even more realistic :-)

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