MDA Corrections for low Temp?

[747dieseldude]

Has anyone heard of factoring the MDA, and the intermediate level-offs on a non-ILS approach, for altimeter errors related with low temperatures?

Thanks for your input.

[Fellow Aviator]

Our company flies frequently at northern parts (very cold parts) of Scandinavia. We have SOP as per OM that altitude corrections are to be made at temperatures below ISA.

Last winter, on occasions, we experienced temperatures -50 below ISA, which will give around +120ft to VOR MDA.

[Jambo Buana]

Do a search on prune as there is lots on this subject. You need to correct all procedure alts inc, mda, om, platform, msas and flap retraction heights. OLnly your rad alt is unaffected. You will find the correction chart in the jeppy or jar ops 1.

[Empty Cruise]

Yep - your company OM part A, Chapter 8 should have the info - or if not there, then look under Supplementary Procedures, Adverse WX Ops.

Of more interest - the MEA/MOCA/MORA/Grid MORA and MSA all need to be corrected as well :ouch:

Finally, correcting the MDH is usually what's being done - if your company OM doesn't help, try adding 4% height per 10 deg. C below ISA :ok:

Empty

[Itswindyout]

There is a table in there, or look in Transport Canada's web site, they have it too....

windy

[Jambo Buana]

This is Transport Canadas info on the subject which is on the John Tullamarine tech site, sorry that table doesnt line up, Im no computer geek!

Figure 9.1—Altitude Correction Chart

COLD TEMPERATURE CORRECTIONS

Pressure altimeters are calibrated to indicate true altitude under ISA conditions. Any deviation from ISA will result in an erroneous reading on the altimeter. In a case when the temperature is higher than the 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 the 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:

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.
IFR assigned altitudes accepted by a pilot shall not be adjusted to compensate for cold temperatures, i.e., if a pilot accepts “maintain 3 000”, an altitude correction shall not be applied to 3 000 ft.
Radar vectoring altitudes assigned by ATC are temperature compensated and require no corrective action by pilots.
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.
ALTITUDE CORRECTION CHART

Height above the elevation of the altimeter setting sources (feet)
Aerodrome Temperature ˚C 200 300 400 500 600 700 800 900 1000 1500 2000 3000 4000 5000
0 20 20 30 30 40 40 50 50 60 90 120 170 230 290
-10 20 30 40 50 60 70 80 90 100 150 200 290 390 490
-20 30 50 60 70 90 100 120 130 140 210 280 430 570 710
-30 40 60 80 100 120 130 150 170 190 280 380 570 760 950
-40 50 80 100 120 150 170 190 220 240 360 480 720 970 1210
-50 60 90 120 150 180 210 240 270 300 450 600 890 1190 1500

NOTES 1: The corrections have been rounded up to the next 10-ft increment.
2: Values should be added to published minimum IFR altitudes.
3: Temperature values from the reporting station nearest to the position of the aircraft should be used. This is normally the aerodrome.
Example: Aerodrome Elevation 2 262ft Aerodrome Temperature -50˚

ALTITUDE HAA CORRECTION INDICATED ALTITUDE
Procedure Turn 4 000 ft 1 738 ft +521.4 ft1 4 600 ft2
FAF 3 300 ft 1 038 ft +311.4 ft 3 700 ft
MDA Straight-in 2 840 ft 578 ft +173.4 ft 3 020 ft
Circling MDA 2 840 ft 578 ft +173.4 ft 3 020 ft


1 CORRECTION derived as follows:

(2 000 ft at -50˚ error) 600 – (1 500 ft at -50˚error)
450 = 150

Altitude difference of above (2 000 – 1 500) = 500
Error per foot difference (150/500)= .3
HAA = 1 738

Error at 1 738 = (1 738 – 1 500) * 0.3 = 71.4 + 450
(error -50˚ at 1 500) = 521.4

2 INDICATED ALTITUDE derived as follows:

Calculated error at 1 738 from above = 521.4
Procedure-turn altitude (4 000) + error (521.4) = 4 521.4

INDICATED ALTITUDE rounded next higher 100-ft increment = 4 600

[Voeni]

they rule of thumb is:

for every 10 deg. below ISA, add 4% to the altitude, i guess... of course, only non-precision appchs, ILS not affected

[titi]

What about DH correction on precision app (ILS CAT 1) while you are not using radio altimeter?

[JEANS42TRF]

http://www.wingfiles.com/files/safety/gettingtogripswithcoldweatheroperations.pdf

[Empty Cruise]

@ titi - yep, anything operated on barometric minima needs to be corrected.

@ Voeni - altitude? I'm not sure... If you have a CAT I ILS aproach (DH 200 ft) to an AD with elevation 5000 ft and OAT is -20C, your correction would be +520 ft for 25C below ISA, giving a corrected DA of 5720 ft. IMHO, the correction only applies to the height, i.e. a correction of 20 ft for a new DA of 5220 ft.


Cheers,
Empty

[titi]

The thing is that most procedures are dealing with MDA and not DA (non precision and not precision app), of course we should make corrections to DA but that is not commonly said for instance in my SOP they only deal with non precision app temperature corrections.

[Looker]

We all know that pressure altimeters are calibrated to ISA. Therefore any deviation from ISA will result in an error which is proportional to the ISA deviation and the height of the a/c above the airfield pressure datum. As previously stated this error is approx 4ft/1000ft per degree C of difference.

Look in the AERAD Flight Information Supplement page AER28 for the correction table ( sorry not familiar with Jeppersen).

Work out the ISA deviation for the airfield temperature/elevation.
Enter table at this ISA deviation, move horizontally to appropriate 'height above airfield' column and extract correction to be added to minima.

This works for all minima DH, DA, MDH, MDA and also for MSA etc.
Thus for ILS app to DH of 200ft at airfield with 5000ft elevation and temp of -20 C correction is......20ft. For NBD with MDH of 600ft to same airfield the correction is .....60ft. For MSA of 8000ft to same airfield the correction is .... 300ft.

Mental gymnastics not required :}

[RatherBeFlying]

Transport Canada's Aviation Safety Letter 4/2006 is not yet on the web, but will eventually appear on: http://www.tc.gc.ca/CivilAviation/Publications/menu.htm

JB has pasted the text from JT's website -- it can also be viewed directly from the TC AIM at: http://www.tc.gc.ca/CivilAviation/publications/tp14371/RAC/9-1.htm#9-16

Scroll down to: Figure 9.1—Altitude Correction Chart

COLD TEMPERATURE CORRECTIONS