Cold weather altimeter correction

[Vargveum 53]

An option in ASN would be good. 

[g_precentralis 191]

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 :)

[AirborneZed 168]

 

 

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

 

Oh Lawd.

[Driver170 42]

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.

[Spin737 102]

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.

[Driver170 42]

Don't know how you do it matt

[jcomm 5,917]

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 :-/

[JoeDiamond 67]

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.

[jcomm 5,917]

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 :-)

[Cristi_Neagu 134]

I'm starting to wonder how much realism is too much realism...

[woodreau 0]

For those looking for how to correct the altitudes for (from the CA-19 page of the jeppesen airway manual)

 

COLD TEMPERATURE CORRECTIONS

 

Pressure altimeters are calibrated to indicate true altitude under International Standard Atmosphere (ISA) conditions. Any deviation from ISA will result in an erroneous reading on the altimeter. In a case when the temperature is higher than ISA, the true altitude will be higher than the figure indicated by the altimeter, and the true altitude will be lower when the temperature is lower than ISA. The altimeter error may be significant and becomes extremely important when considering obstacle clearances in very cold temperatures.

 

In conditions of extreme cold weather, pilots should add the values derived from the Altitude Correction Chart to the published procedure altitudes, including minimum sector altitudes and DME arcs, to ensure adequate obstacle clearance. Unless otherwise specified, the destination aerodrome elevation is used as the elevation of the altimeter source.

 

With respect to altitude corrections, the following procedures apply:

 

a. IFR assigned altitudes may be either accepted or refused. Refusal in this case is based upon the pilot's assessment of temperature effect on obstruction clearance.

 

b. IFR assigned altitudes accepted by a pilot shall not be adjusted to compensate for cold tem-peratures, i.e., if a pilot accepts “maintain 3000 feet” an altitude correction shall not be applied to 3000 feet.

 

c. Radar vectoring altitudes assigned by ATC are temperature compensated and require no corrective action by pilots.

 

d. When altitude corrections are applied to a published final approach fix crossing altitude, procedure turn or missed approach altitude, pilots should advise ATC how much of a correction is to be applied.

 

Then there is a chart with the correction factors based on temperature and height above airport elevation followed by an example of how the corrected altitude is derived.

 

I'm currently on the run, I can post the example later if anyone is interested or I can post the page.

 

Steve w.