Altimeter Cold Temperature Correction Policy
 

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.

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?

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:

Altimeter Cold Temperature Correction Policy
 

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.

"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

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!

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

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.

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

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.

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

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!

correction
 

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:

@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

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"?

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

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.

Changes to Altitudes.
 

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.

ADRUs and cold temp correction
 

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?