Altimeter Cold Temperature Correction Policy

[Challenger 605]

I would like to conduct an informal survey - how many operators/airlines have written operational procedures to address the issue of the altimeter errors due to non-ISA temperatures, and more specifically cold temperature corrections to any minimum IFR altitude? Appreciate your input.

[Rainboe]

You mean there are companies that don't have a cold weather altimeter correction policy? To copy the way people write English these days, all I can say is '!!!!!!!!' (as people like to type)! Shouldn't they be grounded until they learn how to operate?

[kijangnim]

Greetings

:eek: Nobody will give you a list with company names, but it is a big issue in the FMS world, and they are still debating about it, since the solution is to be implemented in the ADRUs :ouch:

[cfm56dash7]

I know of at least one company that publishes corrections as part of their 10-7 program (company unique data published in a Jeppesen format). Others superimpose the data on the approach chart in a custom format.
This still leaves the question of what to do about the crossing restrictions listed in the FMS. Generally, it's a bad plan to go through the arrival and approach and systematically replace the crossing altitudes with temperature corrected values. Way too much chance of a catastrophic 'fat finger' mistake.
One idea proposed is to have unique ARINC 424 records created with the cold weather approach crossing altitudes coded into the database. This would make the entire approach line selectable through the FMS and no mods required 'on the fly.' I personally like this idea but it would lead to ever larger databases and some users are already up against their memory limits. One could limit the damage and calculate just a single cold weather approach, coded to correct for a two-sigma historical low temp and accept the artificially high minima when the weather was a bit warmer.

[bArt2]

One idea proposed is to have unique ARINC 424 records created with the cold weather approach crossing altitudes coded into the database.

"The cold weather altitudes" would not work because it depends on the temperature, so -10ºC is not the same as -30ºC.

Wouldn't it be better to have the possibility to enter a delta T, (negative) temperature deviation from ISA when selecting the approach.

As for the companies. The USAF where I did my pilot training have published these corrections, so does the Belgian airforce where I fly. In the French airforce where I was an instructor for a few years they never heard about this.

Bart

[Dan Winterland]

All operators I'm aware of do. But what is more relevant is what correction to use. ICAO recommend one set of corrections, I'm aware of another set of correction figures and my company uses another correction baed on a percentage of the height. So an airport can have three aircraft approaching all usung diferent correction criteria.

And then there's the question regarding the correction of altitudes when being radar vectored. ICAO Doc 4444 states that an aircraft receiving radar vectors will have cleared altitudes temperature corrected. This happens in airports using PANSOPS, but what abut TERPS? One country using TERPS does, another doesn't. And in some PANSOPS operations, controllers don't always understand their responsibilities as one EGPWS go around I performed once will attest!

It's a minefield!

[bArt2]

According to me the cold temperature corrections have to be done for all altitudes passed the FAF and the corrections are in function of the Height and the temperature deviation.

Whe use a table where you enter at one side with the HAT/HAA and with the temperature on the other side. You then get the amount of feet to add to your minima.

Therefore if you have the same temperature deviation, an approach with a higher HAT will require a bigger correction.

As for the set of corrections, it is merely a correction because the altimeter assumes ISA temperature lapse, where cold temperatures would give a deviation in the unsafe direction (indicating higher than you really are). This error should be the same in all parts of the world.

Bart

[Flyer 1492]

About 10 years agoin the middle of January, I remember a couple of crew members talking about cold temp. corrections for the arrival. There happened to be a chief pilot (from one of the mexican airlines) sitting in listening, after a few minutes he politely asked if he could look at the chart. When he did read the chart his face went white and he then asked if he could make a copy to take back home. Seems they were far below the published altitudes. The airport Kelowna BC and the temps were around -20c on the ground.

[galaxy flyer]

For those wishing to start an anti-Yank thread drift, you would find virtually NO US operators truthfully doing temp comp. Certainly the FAA hasn't pushed it or made it requirement. However, with the rise of FMS Vert Nav approaches, they need to start.

FWIW, my US operator does have it and uses it. On the checklist. But, we are a related to an Canadian operator.

GF

[rubik101]

Cold weather corrections should be made to ALL altitudes from the MSA on down to minimums, not just from the IAF or FAF, as some seem to think.
If you are not applying these corrections when the temps are below 0.C then you are being somewhat foolhardy.
When making any type of approach but particularly a VNAV approach all the hard altitudes should be adjusted appropriately to ensure safe obstacle clearance.

[kijangnim]

Greetings,

The ARINC 424 will not solve any problem since it is the ADRU (Air data side) that needs to be modified, todays solution is, instead of computing a height difference and applying it, we translate the height difference in distance and move forward the FAF, since at you "plateau" altitude you benefit from maximum terrain protection, in both TERPS, and PAN OPS worlds.
Delta ISA X 4 X 1000s of feet.... delta isa =-15 FAF altitude =2000
-15X4X2 = -120 Feet 2000-120= 1880 :}

120 Feet will give 0.4 NM so either you descent to 1880 Feet, or you maintain 2000 and start descending .4 nm after the FAF

[bArt2]

Cold weather corrections should be made to ALL altitudes from the MSA on down to minimums, not just from the IAF or FAF, as some seem to think

http://www.ebzw.be/Tempcorr.gif

[rubik101]

Bart, I see what you have posted but consider this; the FAF may well be at 1500'. There may well be one or more other platform altitudes on the approach from many miles further out than the FAF.
If you want to avoid all these other obstacles then you better make sure that you apply the temperature corrections to ALL the altitudes from the MSA down to touchdown.
Clearing obstacles from the FAF will not stop you hitting the high ground at 20 miles out.
Whoever wrote that never flew into high ground!

[kijangnim]

Greetings,

Below is the FAA, point of view about the subject


The possible result of the above example should be obvious, particularly if operating at the minimum altitude or when conducting an instrument approach. When operating in extreme cold temperatures, pilots may wish to compensate for the reduction in terrain clearance by adding a cold temperature correction. :}

Since the airspace is handling so many aircraft with technology differences, ranging for classic, to FMS advance types, it is very difficult for the time being to impose a technological solution of the problem, so today I think that the idea is that if all aircraft have the same altimeter error, than there is no error within the terminal area. :cool:

[bArt2]

@rubik101.

You have a point, I'm not sure how that would work though, as it could pose a problem if one aircraft makes a correction (before FAF) and another doesn't.

And what about ATC, if you are flying 620 feet higher (indicated) than cleared.

I wonder if ATC uses a correction to vectoring altitudes in cold weather?

Bart

[ray cosmic]

Isn't it one of the P-RNAV requirements not to modify the entries in the route?

BTW, why is it actually that FMS hardware is so ancient in comparison with any PCr "out there"?

[kijangnim]

Greetings Ray cosmic

In fact it is very simple, Aviation industry can only use proven technology, and proven technology is technology on which ZILLIONS of applications of all sorts have been run, and it is a technology with no hidden snags, so the only candidate can only be an OLD TECHNOLOGY. :}
if you consider the time scale it is just fascinating, at project lunch technology selection digs into existing and the winer is a 10 years old CPU, then comes developpement taking 5 years (CPU is already 15 years old tech) then your company gets its first aircraft delivery (1 to 2 year after Roll Out) guess what it 17 years old :ouch: but the worst is to come, how to manage obsolescence :E

[Denti]

If you use IAN (Integrated Approach Navigation) it is not permitted to use cold temperature correction, however you have to enter the airfield OAT into the descent forecast page (or more correctly the ISA deviation). That is of course only valid for the 737 with that type of approach. IAN basicly allows to fly all non precision approach using the approach mode using identical procedures to a normal ILS.

[rubik101]

Ray, you are permitted to alter the heights in the FMC but only in the case of temp. correction. No other alterations are allowed.
Applying a correction at -25C, not something most of us experience very often, makes a difference of 490' to an MSA of 3000'
While you probably won't hit anything if you are 500' lower than you want to be, you most certainly will be well below your MSA and obstacle clearance will be compromised.
I will continue to apply the corrections, as recommended, and if ATC ask me what my altitude is I will tell them the figure with the correction applied.

[Challenger 605]

Can someone explain to me how the ADRU will correct the aircraft's altimeter for cold temperature when the aircraft is flying at minimum IFR altitudes with the altimeter set to the local station pressure (which is derived by considering the surface temperature at the altimeter source)? How does the ADRU know what the temperature at the altimeter source is without some kind of input from the pilot or datalinked from the ground station?

[kijangnim]

Once your sensors have measured values, which after all are just digital data, appropriate software will do the magic.:E

[Challenger 605]

The sensors still do not know what the temperature is at the altimeter setting source. Isn't it that temperature that is the important one when calculating the error of an altimeter at a minimum IFR altitude??

[kijangnim]

Greetings the temperature is a part of the measured data, SAT, TAT, etc...most systems consider tropopause as soon as temp is 56.5 deg. so anything below that altitude is computed as delta ISA :}

[bookworm]

The sensors still do not know what the temperature is at the altimeter setting source. Isn't it that temperature that is the important one when calculating the error of an altimeter at a minimum IFR altitude??

No, it's the mean temperature deviation of the column of air between the altimeter and the altimeter setting source that matters. Thus it might be approximated by the SAT and a standard lapse rate.

[Challenger 605]

Let me see if I got this correct. The ADRU will temperature correct the altimeter. But how does the ADRU know if I am operating at the minimum IFR altitudes (which are the ONLY ones that must be corrected for cold temperature)? Will the ADRU correct ALL aircraft altitudes? If not, what mechanism instructs it to not correct non-min IFR altitudes?

[kijangnim]

Greetings,

The task of the ADRU is to measure data, the FMS (which is a supplemental, advisory device) to use and display these data, and the task of the crew is to be sure that the aircraft is not flying below IFR......:ok:

[Challenger 605]

OK. I still don't get it. The crew still must ensure that they do not fly below the min IFR altiitude but the ADRU will correct for cold temperature errors of the aircraft's altimeter. Let's say that the crew chooses to fly at the min IFR altitude (let us assume that the published min IFR altitude is 3700 feet). The crew descends to 3700 indicated on the altimeter but that is OK because the ADRU compensates for the the cold temperature error and the procedure designed obstacle clearance is not violated. What happens if the crew chooses to fly at 4000 feet? Is that atitude compensated for cold temperature by the ADRU and if it is that aircraft is not at the same atitude as other aircraft without compensation at 4000 feet! At what point does the ADRU not affect the altimeter reading in the cockpit due to temperature (below or above ISA)???

[kijangnim]

Greetings,
I have drifted away from my thoughts, Airway corridors are surveyed for minimum Radio nav reception altitude and terrain protection, the terrain protection takes into account lowest pressure/temperature. Now my argument about ADRU concernes approaches only, particularly NPAs. :}

[kijangnim]

Greetings
Now having said what is above, I personnaly compute the temperature effect on altitude, for single engine ceiling, driftdown, and emergency descent, 4 feet X delta ISA X N(1000)Feets + Indicated.
Where in operate we do have high Mora ...:ok:

[Zeffy]

The incident (a near-CFIT statistic) involving an MD-80 at Kelowna, BC occurred during the procedure turn.

http://www.bluecoat.org/reports/Long_98_Cold.pdf

Cold temp corrections should be applied to all minimum IFR altitudes, not just those inside the FAF.

[kijangnim]

Greetings

During vector radar should take care of it, during the approach, Procedure turn included (Procedure turn to be flown on heading for the Airbus) we should have a minimum temperature for that praticular approach, :}

[john_tullamarine]

During vector radar should take care of it

You place great trust in those who don't risk dying in the event of a miscalculation ... most pilots would opine that a better solution is to be ahead of the radar and KNOW where you are both laterally and vertically ..

[galaxy flyer]

J_T

My humble experience is that a generation younger than ours puts touching faith in radar controllers. :eek: It has been pointed out to me that the controller is responsible for terrain clearance, I've fired back, "but he won't die for his mistake."

GF

[john_tullamarine]

GF,

The acknowledged benefits of being raised by PacMan, I guess ....

I'm just glad that I got to play a lot on the 733 ... if it all looked like it was working, one could leave it on and still fly with an eye on the steam data but with some add-ons to make a few mental processes easier ... otherwise the "OFF" button worked real fine and we went back to flying a la DC3 and one definitely was responsible for one's success in life ...

My simplistic view is

(a) under the surgeon's knife, you don't have a choice

(b) in an aeroplane, you can tell the controller what you are going to do, albeit that it might get up his/her nose a tad .. and, of course, most of us have had the occasional need to do just that ... ATCers (and I have more than a few mates in that discipline) are no less immune from errors than the rest of us ..

[kijangnim]

Greetings,

In my humble opinion, we have to leave people to do their jobs, weither they die or not from their mistakes, because we cannot handle ATC, FO and our own mistakes or errors. Yes human are error making machines, but we have to handle it under error management concept, that is to use methods (SOP) to minimize them. If you do ATC's job on top of your flying tasks, I think you are overloaded, we have safety nets on board ,they are mandatory, such as TAWS, TACAS and it is not a luxury we all know that. BTW I have been flying for 28 years :ok:

[john_tullamarine]

The PacMan comment was not directed to your good self but was a tongue-in-check comment on the differences betwixt us older folk and the young folk starting off in the Industry ...

I concur in part with your comments .. however, in the same way I like to know what the steam gauges are telling me (real stuff) while looking at the pretty pictures (much more processed ..) a basic is knowing where you are and what you are doing .. if you agree with ATC's apparent plan .. then, well and good .. if not .. voice your opinion .. to the extent of diverging from clearance and declaring an emergency if appropriate. I was not concerned about doing ATC's job .. only looking after my own neck to the best of my ability ...

Sitting back and watching the world go by was a fail item in the good old days ... and I can see no reason for the philosophy to have altered ?

[kijangnim]

Greetings
:ok: :ok: :ok: :ok:

[BANANASBANANAS]

Slight thread creep here.

I believe some airports that suffer consistently long periods of cold weather publish approach charts that are 'corrected' down to a nominal temperature and that this cold temperature is published on the chart - hence no temp correction required if the actual OAT is warmer than the cold limit OAT published on the chart.

I dont seem to be able to find an example of such a chart though. Would any of our experienced cold weather operators out there be able to give an example - preferably Jepp?

Thanks.

[DBate]

I believe some airports that suffer consistently long periods of cold weather publish approach charts that are 'corrected' down to a nominal temperature and that this cold temperature is published on the chart

Personally I have not come across any of those already corrected charts (not using Jepp Charts though). But I know that at some airports with very low temperatures during winter period the controllers give you clearances to already temperature corrected values (I think Helsinki is one for example).

But to be honest - I would not count on that. We always correct the values ourselves and advise ATC accordingly if needed. I remeber we had some problems doing that in Kasakhstan; ATC always cleared us to the lower, not corrected altitudes, and complained if we did not comply :ugh:. And they did not even understand why we used corrected values. A short visit of one of our liason pilots to that ATC unit solved the problem. :ok:

[aztruck]

Plenty of cold places in civilisation with no radar and non precision approaches. You better have the back of an envelope handy before top of descent. Fagernes (Norway)being a prime example. Cold wx corrections as per the Jepps table worked out spot on. Flew it once in VMC and got a good view. Next time to minimums(300 agl or thereabouts in blowing snow)and not applying corrections would have been suicide.
Caution best exercised in kasakhstan and other Eastern countries. Double whammy cross checking metric altitude tables AND seeing if they make sense as having been temp corrected for vectoring, especially if QNH requested and they normally use QFE.