View Full Version : ICAO announces IAC date

21st Sep 2016, 01:50
ICAO has just announced the date of International Altimetry Changeover (IAC). IAC wIll take place at 06:00:01 UTC on 01 January 2025. To minimise confusion during the changeover all non-essential aviation activity will be temporarily suspended from 18:00:01 UTC 31 December 2024 to 18:00:01 UTC 01 January 2025. This time period will be designated the No Fly Period (NFP).

After IAC primary altimetry will be referenced to GPS. Secondary altimetry will be referenced to atmospheric pressure with automatic upload of local sea level air pressure (LSLAP) via data link. Tertiary altimetry will be referenced to atmospheric pressure using manual input of LSLAP.

After IAC the Standard Pressure Setting (1013.25 hPa or 29.92 in Hg) will be discontinued. All Transition Altitudes will be withdrawn from use. All altimeter indications will be referred to in terms of Flight Level, which is the indication in feet or metres divided by a factor of 100. In states using metric altimetry the word 'metres' will be added after the numerical value of Flight Level.

Certain categories of aircraft will be exempt from the requirement to use GPS or auto-LSLAP altimetry. These aircraft will require their pilots to set latest known LSLAP for altimetry purposes. Examples include light recreational aircraft, vintage aircraft and aircraft without radio communications equipment.

Pilots requiring their altimeters to indicate vertical displacement from datums other than LSLAP, such as airfield level, may, other regulations permitting, set their altimeters accordingly. The altimeter indications will be referred to as 'height' and will be communicated as absolute value in feet or metres above the chosen datum.

Note: this article is fictitious. Its intention is to show how new altimetry procedures based on current technology could replace the overly complicated procedures in use today, with their associated problem of mis-setting, which in turn can result in airspace infringements, level busts and airprox incidents.

21st Sep 2016, 19:49
If Pilots in doubt think Sky Good, Ground Bad unless fuel gauge says Empty in which case reverse is true.

22nd Sep 2016, 02:16
next thing you know they will get rid of magnetic north!