Cold Temperature Compensation Survey

Sat Oct 05, 2002 12:59 am

The 2002 AIM has a new section on cold temperature operations:

I fly in Southern CA and never have to think about cold weather very much. I don't recall having much training (PPL) in this area besides the usual "Going from a high to a low, look out below" phrase that frankly didn't quite register with me.

I got questions for all pilots out there. Do you compensate for cold temperature when you fly and how do you do it? Thanks.


RE: Cold Temperature Compensation Survey

Sat Oct 05, 2002 2:06 am

Yes, we compensate for low temperatures. We have a "Low Temperature Compensation" page on our FMSes that we actuate when it's appropriate. It simply adds an appropriate amount to the minimum altitudes of the various approaches. As I remember, it starts to come into effectaround -5 C. As a side note, the new Baro-VNAV approaches have minimum temperatures that you must be at or above in order to legally use. (Or so I'm told, I haven't actually seen or flown one yet.) In all fairness, it's normally not much of an issue here in the lower 48 States. Where we usually run into the situation is in Alaska, Canada and northern Europe.

RE: Cold Temperature Compensation Survey

Sat Oct 05, 2002 2:50 am

Hi Jetguy,
Thanks for your reply. You must be using the Universal Avionics FMS? I think that is the only FMS that has the temperature compensation feature.

I was thinking that it's no big deal in the lower 48 states too until I saw the altitude error table in the AIM. It doesn't have to be too cold out to get large errors, especially when you are still flying 3-4 thousand feet above the airport elevations -- in mountainous terrain, this could be a problem.

Best Regards,

RE: Cold Temperature Compensation Survey

Sat Oct 05, 2002 7:48 am

You're correct, they are Universal UNS1-Cs. We have dual installations in all four of the company's bizjets and the King Air 350. They are great boxes. I'm in the middle of a 2-1/2 week vacation so I don't have access to the manuals, but the more I think about it, the more I think the point at which we activate the temperature compensation is +5 C, not -5 C. Like I said, it's not something that we use all that often, but it is getting to be that time of the year where I need to get out the manuals and do a bit of a refresher.
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Joined: Sat Sep 22, 2001 3:17 pm

RE: Cold Temperature Compensation Survey

Fri Oct 11, 2002 7:04 am

The Jeppessen manuals (Enroute) have a section for calculating the altimeter corrections for non-standard cold temperatures.

In short, we take the OAT vs True Altitude and the chart will give the altitude correction. That correction is then added to the altitude flown on the altimeter.

Cold temperatures DO reduce the True height above terrain and it does make a differance. I can remember several years ago, in northern Canada, where a twin Otter clipped a hill in marginal weather because the height was not compenated for.

The Canadian AIP also has correction charts.

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