low temperature correction

[Bumz_Rush]

Can anyone point me to a chart that shows the relationship of temperature to QNH at cold weather airports, for approach corrections. Tried jeps tables and codes, but no joy...Thanks. Bumz

[alf5071h]

Bumz_Rush Try search – low temperature correction.
Also see:
http://www.faa.gov/language/accold.pdf
http://www.bluecoat.org/reports/Long_98_Cold.pdf
http://www.fmcguide.com/media/calgary.pdf

It is surprising how often this subject appears in this forum; this begs the question is the subject taught, and if so how or when is it remembered. Was it fully understood? Furthermore, the many links and references tell what the corrections are, but few tell where or when to use them. Is the industry complacent in these matters, who next will to be caught out by the failure to correct the altimeter and what risk is there of a CFIT event if EGPWS is not fitted?

A recent FSF conference paper reviewed the use of geometric altitude (GPS based) in the EGPWS; this facility shows the true altitude on the EGPWS display (ND), but does not correct the main altimeters. Thus if there is a difference between geometric and the main altimeters then start thinking about cold temp correction or recheck that you have the correct pressure setting. The speaker at FSF also noted the poor understanding that crews have of the actual equipment fit – EGPWS with or without geometric altitude, navigation input GPS or FMS RNAV (FMS RNAV operators beware of potential errors - Addis Ababa event). Also of note were the poor updating of software standards and terrain databases; all free from the manufacturer http://www.egpws.com.

Do the issues above suggest that operators are under strain in the training and knowledge area?

[Bumz_Rush]

I also thought they were in Jeps, but never managed to find the. However the first URL from Alf on page 7 is the ball park figures.
I managed to find the formulae on a previous search. but this is the bogs d*******s. Thanks guys.

[quid]

The Cold Temp correction chart is published by Jeppesen. It's page CA19, but I believe you have to have a Canadian subscription to get it.

The link posted by Mike Jenvey appears to be correct (I didn't check all the values), but it doesn't have the text to clarify how it's used.

In a nutshell, if you "hear" the altitude, i.e., an altitude given by ATC, fly it without correction. They've already done the math.

If you "read" it, i.e., from a Jepp chart, then you must apply the corrections.

In the USA, the AIM now has a section on cold weather altitude corrections.

[BOAC]

bumz - use 'search ' to look for it. There are many threads -
'temperature error' is a good starting phrase

[RoboAlbert]

The tables for temperature error correction are in the Jepp'es we use in Europe - Flight Procedures Part VI. The tables are there but lack in any real instructions on how to use them my advice would be....

If the airfield temperature is below 0ºC the following altitudes are corrected for temperature error:

a. The DA or MDA.

b. For a non-precision approach, all step down fixes inside the FAF or procedure turn.

c. All altitudes in the missed approach procedure.

If the airfield temperature is below 0ºC and the airfield lies in mountainous terrain (3000' or above), the following altitudes are corrected for temperature error:

a. MSA values.

b. All altitudes in the procedure, including those within STARs and SIDs.

c. All altitudes in the missed approach procedure.

Any thoughts anyone?

[alf5071h]

When to use temperature correction.
In addition to the suggestions from RoboAlbert, do not forget the initial descent altitudes, and step downs at non controlled airports. Also remember to temperature correct altitudes during takeoff from non controlled airports, flap retract, acceleration, and turning altitude, etc.

How does this work in the US for a controlled airport by day, but uncontrolled by night; or controlled by a remote centre? I guess it depends firstly on the reference for the pressure setting and second, the type of procedure (precision / non precision) to be flown.

From memory, some time ago, the helpful ATC controllers in Europe would always annotate a temperature corrected altitude clearance. i.e. descent into Innsbruck would be given as “descend to x.yyy ft temperature corrected” (where the lower procedure altitude was x.xxx ft), is this still the approved phraseology?

[Bumz_Rush]

Recent experience as follows:

Several Russian Airports, in Moscow give the corrected QFE setting, as perhaps there is no need to correct a setting that has been read directly from the reference mesuring device.

Next time I will compare the advised QNH, and QFE. Expect optortunity tomorrow....

So does the problem only manifest itself in NON controlled airports, that are working on QNH settings.

Recently been to a Russian airport at 3am, local temp was -30C, (deep inversion layer, at 1000 ft QFE only -10), Not surprising the QFE displayed zero on touchdown.

Bumz,
sorry for not actually helping to clear the fog...

[Empty Cruise]

...and the GS check altitude and FAP if a DME is used, if I may add to RoboAlberts' list. ;)

As alf5071h pointed out, it is surprising to see the question re-appear year after year :( - but encouranging to see that people at least know[I] that a correction must be applied & ask the question. Still, it's found in every OPS1-airlines OM Part A, Chapter 8 - and should be part of the winter LPC/OPC session.

Begs the question if people remember to apply high wind corrections to their MEA/MOCA/MORA when flying over muntaineous terrain - that correction is often in the region of 2000 ft., and if luck is not on your side, it will remove all obstacle clearance margin if not applied. Mind you, a 1200 ft. correction to the MSA alone due to temperature would also do the trick :hmm:

Happy new year to all - and congrats to Danny & the crew, this looks [I]ubercool!

Empty

[Statorblade]

EC,

Do you have any web references for high wind corrections and how to apply them ?

[Empty Cruise]

Hi Stator!

No, no weblinks, but should be found in your OM. My outfit operates with the following rule: With winds above 30 kts, add 500 ft. to all altitudes above the MSA pr. 10 kts above 30 kts. - with a max. correction of 2000 ft.

Would be interesting to see if anyone had a reference in a MET textbook or on the web :)

Brgds fm
Empty

[alf5071h]

Statorblade Altimeter error due to wind speed, see ICAO PANS OPS Vol1 Doc 8168 Part 3 Chapter 4. (http://dcaa.slv.dk:8000/icaodocs/Doc%208168/) The text starts on Page 242 and the tables are on Page 245.
This reference also has low temperature corrections and mountainous area corrections.

[Empty Cruise]

alf5071h :ok:

Just what was needed -thanks!
Empty

[compressor stall]

4*alt above ground/1000 * ISAdev gives you (roughly!) the correction. :ok:

[take_that]

Following along from the original thread.

What is the correct RT when using temp correction?

For example if UK ATC clear you to descend to altitude 4000' on QNH .... What is the correct response if the temperature correction is 300'?

It is an important subject yet after spending 10 years flying around Scandinavia I have yet to hear someone actually correct for Temperature Error over the airwaves. In my experience the airlines that I flew with never corrected for Temperature, although it was written in the Ops Manual. Everyone was aware of it but no one actually did anything about it! Our check altitude at the marker would normally mention 'altitude high due temperature' and the initial brief would mention the fact that we would appear high at the marker due to temperature correction, but thats it.

The thing that really puzzles me is why I didn't hear the local airlines mention this in there replies to ATC. Quite a few winters would see the temperature on the ground fall to -20 degrees. You'd think that if any one would know the correct way of operating in these temps it would be the local national carriers?

From what I can see, there is no published procedure for Temperature Correction in CAP413.

The posters response above sounds like an excellent idea whereby ATC factor the correction into their calls. I'd not heard of this but no that in the places that I fly to the onus is on the pilots to make the correction.

[Empty Cruise]

Well, the problem only arrises when you are flying procedural approaches (e.g. N. Sweden or Norway) when there is no radar coverage. In those cases, I have sometimes had to inform ATC "Cleared the VOR?DME approach 23, be advised we will commence the procedure from non-standard 3300 ft. today due to temperature". Has never been a problem - although sometimes, the ATCO would need an explaination as to why this was so (good way to spend the 12 NM outbound leg! :zzz: ) :ok:

Brgds
Empty

[Statorblade]

Thanks to all for the wind correction references - sorry to deviate from the original topic.

[Dan Winterland]

And not all controllers give you the correction as required as I found out two nights ago at Beijing with a temperature of ISA -18. Being radar vectored to the north of the airfield, we descended to 1200M (3970') as instructed only to almost immediately get a EGPWS 'Terrain, Terrain - Pull Up' which of course we followed. The 1200M was mentioned on procedure for that runway and had we followed the procedure, we would have added 400' as my company makes the corrections easy so we add 10% for ISA -15 to ISA-30. The 1200M is based on an obstuction of 2881'. With a real altitue of 3700' ish, we were now less than 1000' from the obstacle - hence the pull up.

With everything in aviation, don't assume - check. I will be asking if altitudes are temp corrected from now on!

[FullWings]

And not all controllers give you the correction as required as I found out two nights ago at Beijing with a temperature of ISA -18. Being radar vectored to the north of the airfield, we descended to 1200M (3970') as instructed only to almost immediately get a EGPWS 'Terrain, Terrain - Pull Up' which of course we followed. The 1200M was mentioned on procedure for that runway and had we followed the procedure, we would have added 400' as my company makes the corrections easy so we add 10% for ISA -15 to ISA-30. The 1200M is based on an obstuction of 2881'. With a real altitue of 3700' ish, we were now less than 1000' from the obstacle - hence the pull up.

With everything in aviation, don't assume - check. I will be asking if altitudes are temp corrected from now on!
Very, very interesting. I shall be extra careful going into PEK in two days time although I don't know what the Cantonese is for "do you correct for low temperature?"

[Dan Winterland]

They actually speak Mandarin in PEK so Cantonese will be of little use. Their Engrish however, is reasonably good and the ATC fairly good as well. The problem highlighted stemmed not just from their failure to apply a temperature correction, but also as a result of the new procedures introduced a couple of months ago. Everyone is getting to grips with them and our incident may just have highlighted a problem which needs ironing out.

But be careful of those 18 procedures. They take you close to some fairly high ground. :eek:

[alf5071h]

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.

[FullWings]

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...:confused:
...Engrish...
Yes, something like that. ;)

[mutt]

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.....

[alf5071h]

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.

[Empty Cruise]

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 ;)

[mutt]

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

[popay]

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.:ok:

[vikena]

Empty Cruise,

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

Please digress

Vikena

[Dan Winterland]

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

[Empty Cruise]

Mutt,

Yep, nearly added cheeky remark 'bout your location to original post :D - 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 :O ) - 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.). :sad:

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 :p

Empty

[safetypee]

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. (www.wingfiles.com/files/safety/gettingtogripswithcoldweatheroperations.pdf ) 4.3 mb pdf See page 143 onwards.

The FSF also addressed the issue in the ALAR Tool Kit (www.flightsafety.org/alar_resources.html) 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)

[dartman]

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.

[dartman]

...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. :confused:

[albatross]

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

http://www.tc.gc.ca/CivilAviation/publications/tp14371/RAC/9-1.htm#9-16

[popay]

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. :ok:
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.

[dartman]

As you can see, you don't correct the DA for the precision approach. :ok:
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,....
:cool:

[Arctaurus]

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 ? :confused:

[popay]

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.:ok:

[Max Angle]

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.

[Arctaurus]

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.

[popay]

Arctaurus, well as usual if in doubt follow the safest course of action, which in this case is adding 40 ft. However, if you check the design criteria for DA creation it includes corrections for the temperatures, but I couldn't find out down to which T is it good. I haven't experienced corrections for DA, with OAT UP to -30 C, flying in the northern USA. Maybe we were doing wrong, I am not sure. Logically, I agree with you it would makes sense, I am wondering why airbus didn't include it?:}
Cheers.

[dartman]

the minimum temperatures are associated with GPS/RNAV approaches. As you referred to earlier, there is a preprogrammed set of altitudes in the FMC database for the approach. As you can't (or shouldn't) overwrite these altitudes, there is a minimum temperature that these appraoches can be conducted in. If you were to fly the approach in VNAV (or whatever the vertical mode is in the Airbus world) you'd be low at all the IF/FAF/MDA etc altitudes.
CAT I/II/III approaches do not have this restriction.
Again, it's only the CAT I DA that is corrected.
CAT II/III DH's are based on a radar altimeter.

I think the lowest temperature I did an approach in was -53C. And guess who had to do the walkaround after,......Brrrr!!!

[Arctaurus]

I guess the next question is - does anyone have any solid references to temperature compensation automatically incorporated into the DA during the design of a Cat 1 (barometric minima) approach system.

If so, is there a minimum temperature ?

Dartman; At -53 C, there is significant error, I wonder what the RAD ALT was indicating at the cat 1 barometric DA ?

[RYR-738-JOCKEY]

Bumz Rush wrote: Several Russian Airports, in Moscow give the corrected QFE setting, as perhaps there is no need to correct a setting that has been read directly from the reference mesuring device.

Next time I will compare the advised QNH, and QFE. Expect optortunity tomorrow....

So does the problem only manifest itself in NON controlled airports, that are working on QNH settings.


It's the other way around. QNH is derived from QFE(measured pressure at the station) and adjusted by adding 1 hPa pr 30 ft above MSL. Therefore both will be equally accurate in terms of giving us a reference for our altimeters to give us either alt(QNH) or height(QFE), and the temperature corrections apply to both.

[Dick Whittingham]

I am a long way away from active involvement, but maany years ago we were asked to make temp corrections to decision heights/altitudes and to any step-down fixes inside the final app fix if the temp was ISA minus 15 or below For simplicity we were allowed to use airfield temp 0ºC or below for airfields up to 1000ft amsl.

QFE is the actual airfield surface pressure and is not affected by air temperature. The error is engendered in the height gap between the airfield and the aircraft, and varies according to the size of this gap. If you used a false QFE to adjust for temp error at a 500ft decision height your altimeter would be still give false readings at heights above and below 500ft. I don't see how ATC could do this Of course, once you have made your decision at the correct point, with the calculated temp correction incorporated, your indicated altitude is still wrong, but with decreasing error down to touchdown. Your RADALT will be right.

QNH is calculated from QFE, the measured airfield pressure, down to an assumed msl on the assumption that ISA temperatures apply. You set QNH, and the altimeter then back-calculates, again using ISA, and displays field elevation accurately when you are on the airfield, regardless of actual temps. At any height above or below the airfield the altimeter is then subject to temp errors if ISA temperatures do not apply. As with QFE and decision heights, so with QNH and decision altitudes. The size of the temp error depends on the height gap between the airfield and the aircraft (and the temp, of course).

How would the aircraft systems generate a changing temp correction as the aircraft descended, keeping the indicated height correct? Is it possible?

Dick W

[doubleoh]

When flying in Canada we regulary corrected altitudes for temperature...especially NPAs! However, I did a stint in Europe for a while and also flew corrected altitudes including ATC Radar Vectored Altitudes, as we had been told that only Canada corrects RVAs for cold weather.

Obviously, we informed ATC when we corrected their altitudes.

My question is: Does anyone know if this is true? We never had any documentation to back up this claim. It just seemed prudent to apply the corrections in case it was...

[Bumz_Rush]

doubleoh:

I would agree that Canada provides the correct information.

RYR-738-JOCKEY:
Should have said "correct", not "corrected".

QFE is the reference, and QNH is computed based on ISA, and when the temperatre is different the errors appear. Also rememebr in mountainous terrain, the error can be of a large magnitude.

It is perfectly possible for a modern ADC to compensate, as it knows the actual temperatre, at all times, (less any computation lag), thus a corrected height could be displayed. However the lag at normal appraoch speds would be unacceptable.

Arctaurus:

At -53C at a sea level airport you are about 100ft below your displayed altitude, so the baro shows 200ft (cat 1), but you are at 100 (cat 2). The rad alt will show the correct height.
But remember, on a cat 1 approach the RAD alt is not the approved height measuring device.

I have been working in Siberia this winter, and these errors are noticable. BUT in Russia you land on QFE, so no problem.

Bumz

[Empty Cruise]

Bumz_Rush,

ADC will only know actual temperature, not temperature below. That would make passing an inversion in the descent a bit interesting - suddenly you'd loose 1000 ft. of indicated altitude, notwithstanding the implication on obstacle clearance.

How would the ADC solve this problem? :confused:

Empty

[Bumz_Rush]

You are correct, but remember part of the "land init" is surface temperature. So it is possible to calculate something of relevence. The FMC knows the elevation/height plus isa.

I was passing thru a 1000 ft / sfc inversion layer a few weeks ago, from -10 to sfc of -30. Siberia.
The Auto throttle went ape, and was disconnected rapidly.