Cold Temperature Altitude Corrections

[Bill Bridges]

A very good article on Cold Temperature Altitude Corrections.

This information can also be found by NOTAM under Cold Temperature Restricted Airports.

I didn't know anything about adjustments for cold weather until Larry mentioned it.

[Larry sreyoB]

I didn't know anything about adjustments for cold weather until...

I think that's true of a lot of pilots. I certainly didn't understand it until I was well into my career.

In my experience, few CFIs understand it so they can't teach it. Altimeter corrections and inaccuracies are a tough topic for most students. I think most know that they're there but don't really understand them. Their understanding goes only as far as keeping a current altimeter setting set and then taking the altitude reading as "good enough".

It is "good enough" almost all the time. When the temperatures start getting down to around M30, or so, almost isn't good enough for IFR.

The concept that the altimeter setting corrects for non-standard temperature (and pressure) only up to the field elevation of the reporting station is easy to repeat but more difficult to really understand.

The cold temperature correction table has been in the AIM for decades but who really reads the AIM, right?

[Randy Sohn]

I think that's true of a lot ........ but who really reads the AIM, right?

Larry, concur on all - thanks for saying all and also for radar altimeters in some of the places/envirionments I got to.

best, randy

[Larry sreyoB]

also for radar altimeters in some of the places/environments I got to.

Radar altimeters have nearly (completely?) replaced the inner-marker on CAT II/III approaches. I can't recall seeing an IM on an approach in many years. They're also an integral part of GPWS, even after the more to enhanced GPWS which gives earlier warnings based on GPS position and terrain databases. For CAT I approaches, as always, they can aid with situational awareness but have no procedural function.

[Scott Dyer HPN/NY]

What's changed relatively recently is that cold wx correction and restriction symbols appear on (some) iaps. I cover those and the issue generally with my students. But it certainly wasn't covered in my instrument training 30 years ago.

[Larry sreyoB]

What's changed relatively recently is that cold wx correction and restriction symbols appear on (some) iaps. I cover those and the issue generally with my students. But it certainly wasn't covered in my instrument training 30 years ago.

Exactly. It was always in the AIM but few noticed or new when/how to use it.

[Jeff Hartmann]

We all remember "high to low look out below", for pressure and temperature. But honestly, until I was in a recurrent with a couple of Northern Canadians, I never really gave it much thought. In that refresher, Flight Safety reviewed it so I mostly understood it. (retired now, who cares) One thing that was not real clear was when to apply a correction. In some cases approach would issue a corrected altitude, and in some cases not...? ( Fortunately, Glide Slopes need no correction)

I found this... https://www.perfectedflight.com/cold...de-correction/

[Larry sreyoB]

Fortunately, Glide Slopes need no correction

The glideslope doesn't, but the Decision Altitude does.

I figured that you didn't need to start worrying about it until the temperature was down to M25, or so. Warmer than that and the corrections were too small to matter.

I've only applied corrections once. It was in the DC8 going into Thule AFB in Greenland. The difference at G/S intercept was, IIRC, 180'. I can't remember the correction at DA but think is was close to 50'.

ATC will provide the correction when assigning altitudes. You just have to adjust MEA or published minimal altitudes such as on an approach segment, MDA, DA, etc.

On one of my seven trips to Thule I vistited the tower. I asked the controllers about how they applied the correction. Their MVAs were good down to M30. When it was colder than that they increased all MVAs by 1,000'. I was expecting something a little more precise than that but I guess the loss of 1,000' of assignable altitudes isn't that big of a deal when you often go several hours without a single aircraft operation!