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low temperature correction

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low temperature correction

Old 3rd Jan 2006, 15:47
  #21 (permalink)  
 
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Re: low temperature correction

I would be interested to hear from anyone who has had EGPWS alerts, not necessarily due to problems with low temperature; please PM me.
As this new equipment sees wider service it appears that the number of alerts is increasing. Some incidents are of sufficient concern for the authorities to investigate, but others I suspect reflect underlying errors by crew or ATC that could catch us out i.e. failure to correct for low temperature / communicate.
I know of one other low temp EGPWS event during departure from an airport in Norway.
Dan W please check PMs.
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Old 3rd Jan 2006, 15:53
  #22 (permalink)  
 
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Re: low temperature correction

Thanks for pointing all this out - it's not the first time there for me but I have managed to avoid extreme cold so far.

it's interesting when you blast off 36 on a departure in the general direction of Mongolia and get held down below the MSA with traffic above, behind, in front and below you (not to mention out to the side as well). Last time it was CAVOK and the terrain stayed green on the EGPWS. We brief to climb in a holding pattern, if necessary, for perf. but that doesn't include being attacked by other aircraft when you try to do this...
...Engrish...
Yes, something like that.
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Old 3rd Jan 2006, 21:17
  #23 (permalink)  
 
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Re: low temperature correction

If you are given a takeoff obstacle clearance height of XXX feet, or a minimum level off height, do you apply the cold weather correction if the temperature is lower than 0 degrees?

Mutt.....
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Old 3rd Jan 2006, 21:41
  #24 (permalink)  
 
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Re: low temperature correction

mutt If the airport is ‘controlled’ and the controller applies a temp correction and if your are informed of this with the correct terminology, then I believe that your assigned altitude will be safe.
The incident in Norway was from an uncontrolled airport with advisory ATC. In this instance the crew were responsible for the temp correction.
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Old 3rd Jan 2006, 21:46
  #25 (permalink)  

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Re: low temperature correction

Hi Mutt,

I assume that you are talking about obstacle clearance & performance. Yes, in that case ATC don't have a clue what's going down anyway - and the acceleration altitude/FFRA/waddayawannacallit is corrected as well.

Depending on how high your min. acceleration alt. (AA) is, you might wanna apply the correction earlier than 0 deg. C - if you talk 1000 ft. AA, ISA -10 deg. gives a correction of 40 ft. - and with a generous 35/50 ft. obst. claerance to take from...

Empty
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Old 3rd Jan 2006, 22:31
  #26 (permalink)  
 
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Re: low temperature correction

Its the middle of a winters night here and the temp is +20°C, so I can safely say that cold weather ops are not our thing

Question came up regarding why the correction must be applied to the takeoff (performance) acceleration height, the understanding being that as the altimeter read the correct altitude prior to takeoff, how could it be so wrong within the first 1000 feet?

Anyone care to explain?

Mutt
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Old 3rd Jan 2006, 22:35
  #27 (permalink)  
 
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Post Re: low temperature correction

HI folks, interesting thread. I got to pay attention to this as I have PEK twice this month. If its of any use that's what our OM says to that:
8.3.3.11. Temperature Correction
The calculated minimum safe altitudes/heights must be corrected when the OAT is
significantly lower than that predicted by the standard atmosphere.
The correction has to be applied on the height above the elevation of the altimeter setting
source. The altimeter setting source is generally the atmosphere pressure at an airport, and
the correction on the height above the airport has to be applied on the indicated altitude.
• Cold Temperature Altitude Corrections
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 obstacle clearance.
– When altitude corrections are applied to any published procedure altitude, pilots shall
advise ATC how much of a correction is to be applied.
(Canada only: Radar vectoring altitudes assigned by ATC are temperature compensated
and require no corrective action by pilots.)
Table 8.3 - 1 Values to be added by the pilot to minimum promulgated heights/altitudes (ft)
Aerodrome
Temperature
Height above the elevation of the altimeter setting source (ft)
200 300 400 500 1000 2000 3000 4000 5000
0º C 20 20 30 30 60 120 170 230 280
− 10º C 20 30 40 50 100 200 290 390 490
− 20º C 30 50 60 70 140 280 420 570 710
− 30º C 40 60 80 100 190 380 570 760 950
− 40º C 50 80 100 120 240 480 720 970 1210
− 50º C 60 90 120 150 300 590 890 1190 1500
Example: Aerodrome elevation: 1000 ft; Reported Temperature: 0ºC
Result: Fix Published Attitude Height above aerodrome
elevation Correction Indicated Attitude
FAF 4000 3000 170 4170
MDA 1400 400 30 1430
CHeers.
P.S. DAn WInterland, could you please elaborate more detailed on which ARR procedure it happened and where to pay attention, please. PM me if you want.
Thanks.

Last edited by popay; 3rd Jan 2006 at 23:17.
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Old 3rd Jan 2006, 22:44
  #28 (permalink)  
 
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Re: low temperature correction

Empty Cruise,

Altitude corrections for high winds. Never heard of that before .

Please digress

Vikena
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Old 4th Jan 2006, 07:42
  #29 (permalink)  
 
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Re: low temperature correction

JB12A arrival for 18R. (From the South). However, was taken off the arrival and radar vectored onto finals due preceeding traffic.

Last edited by Dan Winterland; 6th Jan 2006 at 02:41.
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Old 4th Jan 2006, 09:21
  #30 (permalink)  

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fish Re: low temperature correction

Mutt,

Yep, nearly added cheeky remark 'bout your location to original post - not really that much of a prob around that corner of the world.

Regarding the altimeter correction - well, ISA-10 deg. equals 4% of the height AAL, so 1000 ft. would give you round 40 ft. The reason it divergers so quickly is - as I'm sure you know (not teaching anyone to suck eggs here ) - that the surface does not contract perceptibly with lower temp, but air does. So even down to ISA-50, your altimeter should still indicate corretly on the ground, but when you passed 1000 ft. AAL indicated, you would actually only be 800 ft. AAL geometrically (4% /10 deg. x 5 = 200 ft.).

vikena,

Only applies in mountaineous (sp?) areas - when the wind moves over a range at high speed, local areas of low pressure may be formed behind, between or over ridges (depending on their actual shape). If transiting such an area, you could be somewhat lower than what your altimeter indicates. I don't think that the effect propagates all the way to a typical cruise level, but if you had to descent into such an area (e.g. decompress), you would feel the effect when approaching the MEA/MORA.

...eeeerrrr....I...eerrr...think

Empty
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Old 5th Jan 2006, 15:30
  #31 (permalink)  
 
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Re: low temperature correction

An alternative, perhaps more practical view of the problems with low temperature altimeter correction, including after takeoff, can be found in the Airbus document Getting to Grips with winter operations. 4.3 mb pdf See page 143 onwards.

The FSF also addressed the issue in the ALAR Tool Kit chapter 3.1, also available in Spanish and Russian!

vikena details of wind correction can be found in ICAO PANS-OPS, see previous post from alf (1 Jan 06)
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Old 5th Jan 2006, 23:11
  #32 (permalink)  
 
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Re: low temperature correction

when clearing you to a lower altitude in a radar enviroment, the controllers typically add a correction to the cleared altitude. i.e. If in the summer they clear you cross a fix at say 10,000 FT, as the temperature drops below IAS, that altitude will rise to 11,000, and then possibly 12,000. This is the case in Canada,the USA, and presumably in Scandanavia. All I can say about our friends in Beijing is,...typical. Obviously the pilot retains ultimate responsibility so if your unhappy with the terrain clearance, advise that you want to remain at some higher altitude. But DONT unilaterally just add 10%/20%etc as I have heard being done. Assuming ATC 'has' added a correction, then you do, there is a potential conflict with a/c descending above, so let ATC know your intentions. You still need to correct the procedural altitudes, DA, MDA, etc.

Last edited by dartman; 6th Jan 2006 at 17:51.
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Old 6th Jan 2006, 17:50
  #33 (permalink)  
 
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Re: low temperature correction

...a further thought. Transport Canada/FAA has you correct below ISA-15, both procedural and DA/MDA etc. However ICAO PAN ops has the procedural altitudes corrected at below ISA-15, but the Minima corrected at ATIS -10 (i.e. ISA-25). Why the difference?



d.
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Old 6th Jan 2006, 19:21
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Re: low temperature correction

Hope that this helps:
Transport Canada - where it does get cold!

http://www.tc.gc.ca/CivilAviation/pu...C/9-1.htm#9-16
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Old 6th Jan 2006, 19:29
  #35 (permalink)  
 
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Re: low temperature correction

Dartman, I am afraid but the information posted by you isn't fully correct. Those are the items you have to apply the corrections to:
On approach, at least the following published altitudes must be increased in low OAT
conditions:
• MSA,
• FAF altitude,
• Step-down altitude(s) and MDA(H) during a non-precision approach,
• OM altitude during an ILS approach,
• Way point crossing altitudes during a GPS approach flown with vertical navigation.
As it is not allowed to modify the altitude constraints of a non-precision approach, a
minimum OAT to fly the approach with the «FINAL APPR» FMGC mode must be
established.
For OAT lower than this minimum, selected vertical navigation must be used.
Remark:
The determination of the lowest useable flight levels by Air Traffic Control units within controlled airspace does not relieve the pilot-in-command from the responsibility of ensuring that adequate terrain clearance will exist, except when an IFR flight is being vectored by radar.
As you can see, you don't correct the DA for the precision approach.
Albatross, Canada isn't only the place to chill the beer. Just yesterday we flown northern China route and the OAT in ZWWW Urumquie (hopefully correct spelled) was -28 C, using that airdrome as an escape airdrome in case of decompression with MSA somewhere around up to 10000 ft, one better make sure to apply corrections.
Cheers.
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Old 6th Jan 2006, 23:32
  #36 (permalink)  
 
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Re: low temperature correction

As you can see, you don't correct the DA for the precision approach.
So your telling me that your company doesn't correct barometric altitudes on an ILS?? (i.e. DA)
CAT 2 and 3 approaches where a DH is used are not corrected as being rad alt based, the aircraft knows how high it is.
As to the list of altitudes to be corrected, well I'm not going to tell anyone how to suck eggs,....
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Old 7th Jan 2006, 07:35
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Re: low temperature correction

Popay
This means that at -30 C, for a sea level airport, you are suggesting for a Cat 1 approach with a nominal DA of 200 ft QNH, the actual altitude will be about 160 ft above the threshold.
That doesn't seem right and I think I would be increasing the DA to 240 ft QNH to recover the required 200 ft.
Or have I got this wrong ?
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Old 7th Jan 2006, 15:54
  #38 (permalink)  
 
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Post Re: low temperature correction

dartman, well from my experience flying in the northern part USA and couple of times in Canada we haven't done it, the items listed in the previous post are from airbus recommendation. However after more carefully studying the matter that's what I have found out from PAN OPS:
4.3.1 Requirement for temperature correction
The calculated minimum safe altitudes/heights must be adjusted when the ambient temperature on the surface is much lower than that predicted by the standard atmosphere. In such conditions, an approximate correction is 4 per cent height increase for every 10°C below standard temperature as measured at the altimeter setting source. This is safe for all altimeter setting source altitudes for temperatures above -15°C.

4.3.6 Small corrections
For practical operational use, it is appropriate to apply a temperature correction when the value of the correction exceeds 20 per cent of the associated minimum obstacle clearance (MOC).

Well, my understanding of this subject would be as follow: You need to apply the corrections on all the other ALT (by the way the PAN OPS speaks about altitudes and heights) to ensure the obstacle clearance as you solely rely on the altimeter as primary guidance source, whereas on ILS your primary source is ILS ground facility, which isn't necessarily affected by cold/hot weather. However, altimeter cross checks (OM or relevant DME reading) are supposed to confirm the correct position on the glide (mainly protection against capturing false GS beam). I think you would agree, that your true height on the glide path, during correct GS following remains the same, regardless of the OAT. What does change is the indicated ALT, which varies with the OAT. Consequently at DA you will be either at lower or higher true ALT (corresponding to the Indicated ALT), again dependable on OAT. However the deviations are negligible (we are talking about 20 ft for DA of 200 ft CATI at sea level assuming off standard temperature lapse rate. At higher elevations, you are good anyway)and would consequently take influence on the required VIS/RVR. How much do you need to increase the VIS/RVR for 20 ft? That's why I think the correction to the DA can be disregarded. With the OAT lower than -15C, i am not really sure.
Arctaurus, don't forget its a off standard temperature lapse rate, which has been calculated as linear change, which isn't always necessarily the case.
I would be interested in other opinions and if anybody has got the experience how to apply the corrections, welcome to share.
Cheers.
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Old 7th Jan 2006, 16:19
  #39 (permalink)  
 
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Re: low temperature correction

With regard to take-off performance and correction of accel. heights. Assuming you are using named runway pages produced by a performance program you will probably find (obviously, check with your own performance people) that the figures have been inspected for the lowest temp. shown on the page (for us it's -20 OAT) and the accel. height shown will be valid for all temperatures shown.

If you are on your own with graphs and terrain charts etc etc. the it's one more thing to take into account.
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Old 7th Jan 2006, 16:35
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Re: low temperature correction

Popay,

The DA for a Cat 1 ILS is obviously at a barometric point which nominally occurs at about 200 ft above the threshold.

Using the tables from my company's manuals, at sea level and -30 C, there is a 40 ft error.

The approach criteria is designed around decisions at the minima, NOT below it, which is where you are by not applying any correction. I don't see temperature limits on any ILS plate from Jepps. What obstacle protection guarantees do you have when initiating a go around at 160 ft.?

So, I would still prefer to apply the correction. It's safe.
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