Richardhead
I just can't believe there is nothing written even on a Jeppesen chart or manual.....
But there is!
Requirement for Temperature Correction
The calculated minimum safe altitudes/heights must be adjusted when the ambient temperature on the surface is much lower than that predicted by the standard atmosphere. In such conditions, an approximate correction is 4 per cent height increase for every 10° C below standard tempera-ture as measured at the altimeter setting source. This is safe for all altimeter setting source alti-tudes for temperatures above -15°
For colder temperatures, a more accurate correction should be obtained from Tables 1 and 2 below. These tables are calculated for a sea level aerodrome. They are therefore conservative when applied at higher aerodromes.
NOTE 1: The corrections have been rounded up to the next 5m or 10 ft increment.
NOTE 2: Temperature values from the reporting station (normally the aerodrome) nearest to the position of the aircraft should be used.
It then lists the values. It's all in the aforementioned reference.
Pittdown man
That tongue in cheek process really is actually the most accurate formula for working out cold temperature correction. It even takes into account the variation in the value of 'g' with altitude. ICAO doc 8186 refers.
