Flight Operations Briefing Notes Supplementary Techniques Altimeter Setting - Use of Radio Altimeter(5)

 
 
 
 
 
 
 
 
 
 
 
 
Figure 4
Effect of OAT on True Altitude
 

. .

 
As a consequence, when performing an ILS approach – for example - with a published 2000 ft glide-slope interception-altitude and a – 40° C OAT, the glide-slope interception altitude (i.e., altitude selected on FCU) should be increased by 480 ft  (refer to the example shown on Table 2).
The ICAO PANS-OPS, Volume I, provides corrections to be added to the published minimum safe altitudes (if using QNH) / heights (if using QFE).
The temperature correction to be added to the indicated altitude (height) is a function of the aerodrome surface temperature (OAT) and of the desired true altitude (height) above the elevation of the altimeter-setting source, as illustrated by Table 2.

 
( Source – ICAO PANS-OPS )
Table 2
Low OAT Correction (ft) to be Added to Published Altitudes / Heights
Flying into a low temperature area has the same effect as flying into a low-pressure area; the aircraft is lower than the altimeter indicates.
These effects are summarized and illustrated in Table 3, featuring a well-known aviation golden rule “ Look Out Below ! ” :
 
 From
 To
 Effect on Altitude
 
Atmospheric Pressure
 High
 Low
 True altitude is lower than indicated altitude !
 
OAT
 Warm
 Cold
 

 
Table 3
The Golden Rule of Altitude Awareness
In most countries, the pilot is responsible for performing the low-OAT correction, except when under radar control in a radar vectoring area; in this case, the controller normally is responsible for terrain clearance, including accounting for the cold temperature correction (when issuing altitude instructions). 
Nevertheless, the operator and/or pilot should confirm this responsibility with the air traffic services of the country of operation.
The temperature correction on altitude affects the following published altitudes, which therefore should be increased under low OAT operation:
MEA;

Airport sector MSA;

SID / STAR / Approach segments minimum safe altitude;

SID / STAR altitude constraints;

Procedure turn / holding minimum altitude;

FAF altitude;

Step-down altitude(s) during a non-precision approach;

MDA(H) during a non-precision (non-ILS) approach;

DA(H) during a CAT I ILS approach; and,

OM crossing altitude during any ILS approach (for altitude check purposes).

For RNAV approaches conducted with Baro-VNAV vertical profile navigation, the minimum published altitudes take into consideration (for recent RNAV procedures only) the effect of low OAT down to a minimum indicated on the approach chart.
　
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