Cold Weather Altimeter corrections
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Cold Weather Altimeter corrections
Have a question boys.
When flying in extreme cold conditions and correcting STAR altitudes. Does one apply the correction for Final Approach Fix altitudes also?
When flying in extreme cold conditions and correcting STAR altitudes. Does one apply the correction for Final Approach Fix altitudes also?
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I applied the correction to the final approach fix and landed up high on sighting the airfield.Had to go around.
On the next approach we did it the old fashioned way and managed to land.
What do you think?
On the next approach we did it the old fashioned way and managed to land.
What do you think?
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You were high on the approach after applying the cold temperature corrections.........................were you in a radar environment at the time??
When to Apply Corrections:
When the aerodrome is 0°C or colder, or for higher elevation aerodromes the ISA deviation is -15°C or
colder, temperature error correction must be added.
ARRIVALS
Note: Alterations to navigation database altitude constraints are not permitted when performing
MANAGED non-precision approaches (incl. PRNAV); however such approaches without low
temperature altitude correction are approved, provided that the OAT at the aerodrome is not below
ISA -25°C. e.g. not below -10°C at sea level, or published temperature.
Otherwise:
In a radar environment any altitude (height) assigned by ATC will already have been compensated for
temperature, hence low temperature corrections should be made ONLY to approach fix crossing altitudes
and the DA or MDA.
In a non-radar environment all altitudes published in an approach procedure should be corrected. When
crews intend to apply corrections to the FAF/platform altitude, procedure turn or missed approached
altitude, they MUST advise ATC of their intention and the correction to be applied.
Note: In a metric environment ATC must be advised of the increment in metres applied to the
height (QFE) in metres.
When to Apply Corrections:
When the aerodrome is 0°C or colder, or for higher elevation aerodromes the ISA deviation is -15°C or
colder, temperature error correction must be added.
ARRIVALS
Note: Alterations to navigation database altitude constraints are not permitted when performing
MANAGED non-precision approaches (incl. PRNAV); however such approaches without low
temperature altitude correction are approved, provided that the OAT at the aerodrome is not below
ISA -25°C. e.g. not below -10°C at sea level, or published temperature.
Otherwise:
In a radar environment any altitude (height) assigned by ATC will already have been compensated for
temperature, hence low temperature corrections should be made ONLY to approach fix crossing altitudes
and the DA or MDA.
In a non-radar environment all altitudes published in an approach procedure should be corrected. When
crews intend to apply corrections to the FAF/platform altitude, procedure turn or missed approached
altitude, they MUST advise ATC of their intention and the correction to be applied.
Note: In a metric environment ATC must be advised of the increment in metres applied to the
height (QFE) in metres.
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Cold WX Altitude corrections
4% per 10 deg below ISA of the height above the elevation of the altimeter setting source.
Example.
Assume airport elevation 1000' & OAT = -2degress.
Approach minima = 1200' altitude. (200' AAL)
Therefore ISA deviation is -15.
Altitude correction = 1200 x 0.04 x 15/10 = 72'
Therefore an Indicted Altitude of 1272' = a True Altitude of 1200'
But sebxl has the simplest formula.
4 x 15 x 1200/1000 = 72'
Example.
Assume airport elevation 1000' & OAT = -2degress.
Approach minima = 1200' altitude. (200' AAL)
Therefore ISA deviation is -15.
Altitude correction = 1200 x 0.04 x 15/10 = 72'
Therefore an Indicted Altitude of 1272' = a True Altitude of 1200'
But sebxl has the simplest formula.
4 x 15 x 1200/1000 = 72'
Bobdazzle,
The correction is a proportional one and not a single fixed number. The amount of the correction reduces as one descends towards the airfield.
EXAMPLE:
Airfield elevation sea level
OAT -25C
deviation from ISA= -40
Cold temperature correction = 4 x 40 per 1000ft above the airfield
(i.e. 160ft per 1000ft)
If you had a 'STAR altitude' of 5000ft, the correction would be 160 x 5 = 800ft.
You would fly at 5800ft (having advised ATC first, of course)
At 'descent point' of say 2000ft the correction would be 160 x 2 = 320ft.
You would fly at 2300ft
At the FAF altitude of say 1200ft the correction would only be 160 x 1.2 = 192ft so you would fly at 1400ft
At the MDA of say 300ft the correction would be 160 x 0.3 = 48ft so you would fly at 350ft.
I may have mis-understood you but you seemed to imply that you had one correction figure that you applied to all phases of the arrival and approach.
You can see from the above that the correction value reduces as one gets closer to the ground. It is most important at MSA and hardly relevant at most MDAs or DAs.
If you applied a single large correction for all phases, it would explain why you were high at the final approach fix. The fact that the correction is actually rather small at the FAF would explain why you did not feel that you were too low when you did it the 'old fashioned way'.
Hope this helps.
The correction is a proportional one and not a single fixed number. The amount of the correction reduces as one descends towards the airfield.
EXAMPLE:
Airfield elevation sea level
OAT -25C
deviation from ISA= -40
Cold temperature correction = 4 x 40 per 1000ft above the airfield
(i.e. 160ft per 1000ft)
If you had a 'STAR altitude' of 5000ft, the correction would be 160 x 5 = 800ft.
You would fly at 5800ft (having advised ATC first, of course)
At 'descent point' of say 2000ft the correction would be 160 x 2 = 320ft.
You would fly at 2300ft
At the FAF altitude of say 1200ft the correction would only be 160 x 1.2 = 192ft so you would fly at 1400ft
At the MDA of say 300ft the correction would be 160 x 0.3 = 48ft so you would fly at 350ft.
I may have mis-understood you but you seemed to imply that you had one correction figure that you applied to all phases of the arrival and approach.
You can see from the above that the correction value reduces as one gets closer to the ground. It is most important at MSA and hardly relevant at most MDAs or DAs.
If you applied a single large correction for all phases, it would explain why you were high at the final approach fix. The fact that the correction is actually rather small at the FAF would explain why you did not feel that you were too low when you did it the 'old fashioned way'.
Hope this helps.
Canada Air Pilot Cold Temperature Correction Table
See page 21 for Cold Temperature Correction Table
http://charts.ivao.ca/cap_gen.pdf
Thanks to IVAO for hosting
http://charts.ivao.ca/cap_gen.pdf
Thanks to IVAO for hosting
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Jepps...
..and use the charts in the Jepps.
No requirement under radar control.
If you're established on the ILS, on glideslope, the final fix reference altitudes
are only a reference as you are established on the glideslope.
For CAT 1 approaches, corrections MUST be made to the DH, otherwise you will descend below CAT 1 minimums.
CAT 2 and CAT 3 are predicated on the use of RA minimums and are not adjusted.
No requirement under radar control.
If you're established on the ILS, on glideslope, the final fix reference altitudes
are only a reference as you are established on the glideslope.
For CAT 1 approaches, corrections MUST be made to the DH, otherwise you will descend below CAT 1 minimums.
CAT 2 and CAT 3 are predicated on the use of RA minimums and are not adjusted.
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Question from a Performance Engineering type -
Altitude is corrected for temp and this ensures obstacle clearance. Shouldn't you also correct FPA. If you don't you're going to end up long (high).
The actual FPA flown is a calculated by the FMS using barometic (Alt) and inertial data (for Vertical Speed). Even though you cross the FAF at the right altitude (once corrected for temp) the aircraft will then fly the final approach having calculated a required vertical speed from that corrected altitude but maintaining the FPA input from the approach plate.
In that situation - If you don't correct the FPA - you will end up (high).
To avoid being high - get the corrected the angle from the atan of the corrected hgt/distance to field.
FPA restrictions would be respected because the aircraft is still flying the required FPA. (It just thinks it flying a steeper FPA)
Given the decrements used to change altitude on the FCU (100 ft) and the relatively minor differences in corrected FPA's you could put together a single table of FPA corrections that would cover virtually every situation.
Yes? No?
Altitude is corrected for temp and this ensures obstacle clearance. Shouldn't you also correct FPA. If you don't you're going to end up long (high).
The actual FPA flown is a calculated by the FMS using barometic (Alt) and inertial data (for Vertical Speed). Even though you cross the FAF at the right altitude (once corrected for temp) the aircraft will then fly the final approach having calculated a required vertical speed from that corrected altitude but maintaining the FPA input from the approach plate.
In that situation - If you don't correct the FPA - you will end up (high).
To avoid being high - get the corrected the angle from the atan of the corrected hgt/distance to field.
FPA restrictions would be respected because the aircraft is still flying the required FPA. (It just thinks it flying a steeper FPA)
Given the decrements used to change altitude on the FCU (100 ft) and the relatively minor differences in corrected FPA's you could put together a single table of FPA corrections that would cover virtually every situation.
Yes? No?
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nnc0,
If the crossing altitude/height is corrected for temperature, the angle should be the desired original angle and subsequently the FPA would not require any correction, assuming that you are flying the Flight Path Angle.
In practical terms the glidepath generated from the ground will not change and for example the altitude corrections on an ILS is to enable FAF altitude cross check and Minimums correction to prevent descending below the desired decision height.
If the approach is a non-precision type, the calculated FPA will still remain the same, if in fact you are flying a specific descent or glidepath angle, and the corrections to the altitude are to provide proper heights at procedure altitudes and fixes, (ie procedure turn/inbound prior to FAF, FAF crossing altitudes, MDA, MSAs etc.) as well, the vertical speed, if sourced from a barometric source will also reflect the changes.
The geometry remains the same, the indication on the barometric altimeter/VSI are merely reflecting the errors due to the cold air mass and are subsequently corrected to ensure the geometry remains the same (and the obstacles are cleared).
BD
If the crossing altitude/height is corrected for temperature, the angle should be the desired original angle and subsequently the FPA would not require any correction, assuming that you are flying the Flight Path Angle.
In practical terms the glidepath generated from the ground will not change and for example the altitude corrections on an ILS is to enable FAF altitude cross check and Minimums correction to prevent descending below the desired decision height.
If the approach is a non-precision type, the calculated FPA will still remain the same, if in fact you are flying a specific descent or glidepath angle, and the corrections to the altitude are to provide proper heights at procedure altitudes and fixes, (ie procedure turn/inbound prior to FAF, FAF crossing altitudes, MDA, MSAs etc.) as well, the vertical speed, if sourced from a barometric source will also reflect the changes.
The geometry remains the same, the indication on the barometric altimeter/VSI are merely reflecting the errors due to the cold air mass and are subsequently corrected to ensure the geometry remains the same (and the obstacles are cleared).
BD
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nnc0, that's exactly the reason why VNAV mode and fully managed approach is limited to the minimum OAT of -15 C at sea level. It also should be depicted on the chart till which temperature this particular approach can be flown in case of a RNAV. The reason is that the codded approach isn't ought to be modified. Unless ATC applies low temp corrections one is ought to apply it to all promulgated ALT.
Below the approved temperatures the approach will have to be flown selected with increments applied. In fact your true altitude will remain the same therefore the trajectory will be the same as well.
Cheers.
Below the approved temperatures the approach will have to be flown selected with increments applied. In fact your true altitude will remain the same therefore the trajectory will be the same as well.
Cheers.
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Originally Posted by K.Whyjelly
In a radar environment any altitude (height) assigned by ATC will already have been compensated for temperature...
It's been discussed before so a search may give some useful background.
