PPRuNe Forums - Cold weather Alt

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Barronflyer

27th Oct 2014 02:30

Cold weather Alt

Hi there

I'm hoping someone can provide assistance on the following

I've been studying the cold weather alt tables. I understand how the correction to MSA is accomplished but I'm a little confused with correction to procedural altitudes (IAF,FAF, MDA etc). Should I be correcting the FMC altitudes only in this regard or am I required to set the MCP ALT to these adjusted altitudes. If so do I need to advise ATC each time I do this?

And if ATC clear me e.g. to ANY altitude am I required to set that altitude exactly with no correction?

Any info would be appreciated

galaxy flyer

27th Oct 2014 02:50

Is TEMP COMP available in your FMS? If so, follow those altitudes once the temp deviation is loaded and activated. If not, compute the temp correction, advise ATC of the indicated altitude being flown for the existing temp. Canadians an d most cold weather areas, except the US, understand the need for temp comp.

You comp for all altitudes from IAF inbound. Set the ALT SEL to the corrected altitude, VNAV, if the VNAV can be temp comped, will follow temp corrected altitudes.

ahramin

27th Oct 2014 04:29

The point is that your altimeter will overread, leading you to be lower than you think you are. If you correct all the altitudes in your FMC, but then go to lower altitudes by intervening with the MCP ... let's hope there's no terrain.

If you are being radar vectored, the altitudes ATC gives you should already be temperature corrected so no need to apply any more. If you're in doubt just ask them. Any other altitudes on approach or missed approach should be corrected, but for altitudes that could affect ATC, such as MA altitude, make sure you tell them what you are doing.

JeroenC

27th Oct 2014 05:58

Cold weather Alt

Not all altitudes from the IAF but below the temperature corrected MSA needs to be corrected (in our company at least, EU OPS).

latetonite

27th Oct 2014 10:57

Now I am getting confused. Does the ISA deviation entry in the FMC adjusts the altitudes from the FAF inbound?

Denti

27th Oct 2014 13:10

Depends on your FMC. Our A320 and 737 FMCs do not do automatic temperature correction although they do have all the information needed. So we have to do it ourselves, however our SOP only require it if the OAT at the airport is -15°C or below.

latetonite

27th Oct 2014 15:10

Thought so as well. Thanks.

Skyjob

27th Oct 2014 18:14

Different outfits, different rules...

In some cold weather correction is to be applied below 0C.
In some aircraft types it can be selected in FMC.

In all cases where it cannot it need only be applied to all MSA and below altitudes, thus anything in FMC which depicted on a chart is at or below MSA requires a cold weather correction.

For RNP approaches, different rules apply inside the FAF, where no corrections are allowed, to make it more awkward.

Arfur Dent

27th Oct 2014 22:15

As with many things in aviation, the Lawyers will get it right after the 'event'. If you currently operate a lot into very cold temps, ask your Operating Authority to simplify and explain exactly what you are required to do in all different situations you may find yourself in. Do it now, not some time later........

SR-22

27th Oct 2014 23:14

All MSA and below including RNP (except Baro VNAV from and including the FAF down towards the DA/MDA(which should be corrected))

InSoMnIaC

27th Oct 2014 23:52

Quote:

however our SOP only require it if the OAT at the airport is -15°C or below

Denti do you mean ISA-15 ?

Denti

28th Oct 2014 07:01

Nope.

Quote:

Apply the altitude corrections when needed:

• No corrections are needed for reported temperatures above -15°C or if the aerodrome temperature is at or above the minimum published temperature for the procedure being flown;

Minimum temperatures are only published for baro VNAV procedures and all of those we use are corrected to -15°C.

aterpster

28th Oct 2014 14:22

Quote:

If you are being radar vectored, the altitudes ATC gives you should already be temperature corrected so no need to apply any more. If you're in doubt just ask them.

In North America, Canada does, the U.S. doesn't.

ManaAdaSystem

28th Oct 2014 17:18

All minimum altitudes should be corrected for low temp except procedures that are designed down to a certain temp, normally -15 or -20 C. These RNP procedures are not allowed to be flown outside the minimum temperatures.
No, not all ATC units correct for low temp. If they clear you to, say 3000 ft, and this is the MSA, add the required correction and tell them you will maintain this altitude due low temp.

If your FMC autocorrects for low temp, good for you. I have never used one that could do that.

FE Hoppy

28th Oct 2014 21:50

If a procedure has a published minimum temperature there is no need to correct above that temp and it can be flown below that temp if temp correction is applied.

It's not rocket science.

ManaAdaSystem

28th Oct 2014 23:24

It appears to be.
No, you can not fly a procedure designed for temps down to -20 at lower temps.
No corrections allowed.

FE Hoppy

29th Oct 2014 12:40

No It isn't.

PANS OPS:

Quote:

4.3.5.2.2 Determination of minimum promulgated temperature. Determine the minimum probable temperature (the temperature correction is obtained from Appendix A to this chapter) and round it down to the next lower 5°C increment. Then:
a) the FAS for that temperature shall be calculated (see 4.3.5.2.3) and, if less than 2.5°, the promulgated VPA shall be increased to ensure the FAS at minimum temperature is equal to or greater than 2.5°; and
b) the length of the preceding segment shall be reviewed to ensure it meets the relevant requirements for minimum distance before vertical path intercept.
Note 1.— One suitable method of obtaining the minimum temperature is to obtain the mean low temperature of the coldest month of the year for the last five years of data at the aerodrome elevation. Round this temperature down to the next lower 5°C increment for promulgation. Obtain the cold temperature correction applicable for this temperature, the aerodrome elevation, and FAP height using the criteria in the appendix to this chapter.
Note 2.— No minimum temperature restrictions apply to aircraft with flight management systems incorporating final approach temperature compensation.
Note 3.— No minimum temperature restrictions apply to aircraft with flight management systems incorporating approved final approach temperature compensation, provided the minimum temperature is not below that for which the equipment is certificated.

;)

cosmo kramer

30th Oct 2014 12:07

Quote:

aterpster

Quote:

Quote:
If you are being radar vectored, the altitudes ATC gives you should already be temperature corrected so no need to apply any more. If you're in doubt just ask them.

In North America, Canada does, the U.S. doesn't.

Are you sure about this? During radar vectors, ATC is responsible for providing you with terrain clearance.

Are you basing this on personal experience? Or is that written somewhere. If you are basing this on experience only, it might not be transparent to you that ATC is doing the correction. I.e. you might be cleared to the same altitude on a hot summer day and a cold winter night, because the minimum radar vectoring altitudes are that much lower that the procedure altitudes, to absorb the corrections.

ahramin

30th Oct 2014 22:35

Quote:

Not all altitudes from the IAF but below the temperature corrected MSA needs to be corrected (in our company at least, EU OPS).

A good point. No point correcting altitudes that are for ATC procedures rather than terrain clearance. Again the simple point here is that you are going to be lower than you altimeter says you are, which should make it obvious when you need a correction.

And you mean a t° corrected MSA right?

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