Temp corrections for "Extreme cold"

[Freeport_Flyer]

Looking through the latest AIP at temp correction for IAP (RAC 9.17.1) and the term "Extreme cold weather" is used as the caveat to temp correct the min altitudes plus MSA and Arc altitudes. "Extreme cold weather" is not defined in the AIP. I seem to remember using -30c as the point at which temp correction was applied to all altitudes.

What one person may define as extreme cold may differ from another, eg. Vancouver pilot vs Yellowknife pilot.

Is this term defined anywhere?

[telex]

Looking through the latest AIP at temp correction for IAP (RAC 9.17.1) and the term "Extreme cold weather" is used as the caveat to temp correct the min altitudes plus MSA and Arc altitudes. "Extreme cold weather" is not defined in the AIP. I seem to remember using -30c as the point at which temp correction was applied to all altitudes.

What one person may define as extreme cold may differ from another, eg. Vancouver pilot vs Yellowknife pilot.

Is this term defined anywhere?

Can't help you with a definition but have a look at Note 2.

"2. Values should be added to published minimum IFR altitudes."

All altitudes need to be corrected. -30 has no relevance.

[photofly]

Whenever the altimeter setting source is below freezing, it’s a requirement to correct altitudes for temperature.

[iflyforpie]

I've never heard of just correcting the lower altitudes.

Sure, your obstacle clearances are higher on Sector or 100 safe... but so is the altimeter reading error. What's a 40 feet correction on an MDA or DH is 400 feet on some sector altitudes.

[Freeport_Flyer]

Then why differentiate what to do in extreme cold weather at all? Quote from newest AIP below. It’s in a “blue section” which I believe highlights a change.

In conditions of extreme cold weather, pilots should add the values derived from the Altitude Correction Chart to the published 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.

If you are required to correct these all the time when temps are below zero why bother making special note? I believe temp correction is for MDA / DH / FAF when below zero and you only correct the MSA and arcs for extreme cold.

[photofly]

All minimum altitudes get corrected. CAP GEN p33.

Corrections are applied so you don’t hit terrain and obstacles. They don’t care what the title of the restriction is. If you know a Correction is appropriate, why would you *not* want to apply it? When you’re 7000’ above your altimeter setting source your 1000’ clearance over that ridge can have disappeared.

[AuxBatOn]

So, I know it doesn’t apply to civilians but military guidance is temperature correct only altitudes inside the FAF, unless it’s -30C or below, or the airport is located in a mountaneous region where you temperature correct all altitudes.

[GoinVertical]

I've flown with quite a few "older" captains who only bother to temp comp the FAF and Minimums (most of the time it's the same guys that still think calling level is required...).

Similar topic, why do LNAV/VNAV procedures have minimum usable temperatures (normally around -25)? If you temp comp every waypoint you should still have a safe and usable slope, no?

[AuxBatOn]

Similar topic, why do LNAV/VNAV procedures have minimum usable temperatures (normally around -25)? If you temp comp every waypoint you should still have a safe and usable slope, no?

Because your pseudo glidepath is based on baro information which is not temperature corrected.

[GoinVertical]

Similar topic, why do LNAV/VNAV procedures have minimum usable temperatures (normally around -25)? If you temp comp every waypoint you should still have a safe and usable slope, no?

Because your pseudo glidepath is based on baro information which is not temperature corrected.

Last I checked my FMS temperature corrects the entire slope... if each waypoint on the slope is temperature corrected then won't the pseudo glidepath be correct? If I throw LPV on one and select LNAV/VNAV on the other the slope looks the same to me.

[AuxBatOn]

Similar topic, why do LNAV/VNAV procedures have minimum usable temperatures (normally around -25)? If you temp comp every waypoint you should still have a safe and usable slope, no?

Because your pseudo glidepath is based on baro information which is not temperature corrected.

Last I checked my FMS temperature corrects the entire slope... if each waypoint on the slope is temperature corrected then won't the pseudo glidepath be correct? If I throw LPV on one and select LNAV/VNAV on the other the slope looks the same to me.

Yours may. Some don’t. ICAO guidance allows pilots flying temperature compensated VNAV glidepath to ignore the min temperature limitation. Not sure how it works in the civilian world. Will become moot with more and more aircraft equipped with Augmented GNSS systems.

Edit: here’s the ICAO guidance: https://www.icao.int/SAM/eDocuments/13P ... %20eng.pdf Para 13 is if interest.

[GoinVertical]

Yours may. Some don’t. ICAO guidance allows pilots flying temperature compensated VNAV glidepath to ignore the min temperature limitation. Not sure how it works in the civilian world. Will become moot with more and more aircraft equipped with Augmented GNSS systems.

Edit: here’s the ICAO guidance: https://www.icao.int/SAM/eDocuments/13P ... %20eng.pdf Para 13 is if interest.

Excellent reading material! Good to know, thank you!

[goingnowherefast]

Temperature corrections are not mandatory. They use the term "should" instead of the word "shall", making it optional. It's pretty dumb not to use them, but that's another discussion. So to give baro VNAV a regulated level of safety and low minimums during normal temperatures, they need to specify a minimum temperature.