getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(75)

-
 Read that the correction on the altimeter indication must be 105 ft.

QNH ALTITUDE MINUS TERRAIN ELEVATION (ft)  .  .Z CORRECTION (ft) 
500  1000  1500  2000  2500  3000 
.ISA  -10 °C  -17  -34  -51  -68  -85  -102 
-20 °C  -35  -70  -105  -140  -175  -210 

-30 °C  -52  -104  -156  -208  -260  -312 
-40 °C  -70  -140  -210  -280  -350  -420 
TRUE ALTITUDE = QNH ALTITUDE + .Z Note: A constant .ISA from ground to airplane level has been assumed 

● Application of Low altitude corrections.
Corrections on an indicated altitude have to be applied on the published minimum altitude except when the criteria used to determine minimum flight altitudes are already published and take into account low temperature influences (Mentioned on AIP).
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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,

.
Waypoint 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.
E2.2 High altitude temperature corrections (En-route)
Formula: IA = TA x T°std / T°
IA = Indicated Altitude
TA = True Altitude
T°std = Temperature standard (°K)
T° = Actual temperature (°K)

Example:
Let’s assume that the actual altitude is 16500 ft and actual temperature is -48°C.
T°std: temperature standard at 16500 ft = -18°C = 255°K
T°: actual temperature at 16500ft = -48°C = 225°K (ISA -30°C)
IA = 16500 x 255/225 = 18700 ft
The following chart is illustrated in the FCOM, and is based on the above-noted formula.
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FOR HIGH ALTITUDE USE

ALTITUDE (QNH) (1000 FT)40
30
2018700 10
0 10 16500 20 30 40
ISA -30ISA °C A+°30C 
IS

TRUE ALT ITUDE (1000 FT) 

Figure E3
This formula doesn’t take into account the elevation of the altimeter setting source. It has to be used en route and must not be used to adjust low altitude.
　
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