A Complete Manual for Conducting International Flight Operations
Cold Weather Altimetry
Cold Weather Altimetry
With longer range aircraft, a higher probability exists for using isolated airports that are subject to temperature extremes. Pilots shall be aware of cold weather altimetry procedures and shall exercise EXTREME CAUTION WHEN FLYING IN PROXIMITY TO OBSTRUCTIONS OR TERRAIN IN LOW TEMPERATURES. Extremely low temperatures will cause serious errors that result in the airplane flying lower than what is indicated on the altimeter. When considering the effects of unusually hot or cold temperatures, crews shall determine the temperature deviation from standard. If the temperature is warmer than standard, the aircraft will be flying higher than what is indicated on the altimeter. If the temperature is lower than standard, the aircraft is flying lower than what the altimeter indicates.
ICAO Cold Weather Altimetry Errors
The table above is derived from ICAO formulas and indicates the potential for altimetry errors when cold temperatures exist. To use the table, take the height of a fix above the airport i.e. 1000’ AGL and reference the reported temperature -30 degrees C. The result would indicate that the aircraft would be 190’ lower than what the altimeter indicates. Should a correction be required for a height above airport greater than 5,000 feet, the 5,000 foot column shall be used.
Pilots shall also not make adjustments to altimeter settings as a means to correct for cold temperatures. The only correct method of compensating for cold temperatures is to cross fixes at higher altitudes and advise ATC when applying this correction.
“Pilots must not apply cold temperature compensation to ATC assigned altitudes or when flying on radar vectors in lieu of a published missed approach procedure. Pilots should query ATC when vectors to an intermediate segment are lower than the requested intermediate segment altitude corrected for temperature.”
Domestic Cold Temperature Restricted Airports
In the United States the FAA has established approximately 400 airports that require cold temperature altimetry corrections. Generally the requirement for cold altimetry corrections is displayed in the notes section of the approach chart as seen for the RNAV 3 for Laramie, Wyoming.
In the above example the notes indicate that cold temperature altitude correction is required at or below - 35 degrees C. It is important to note that not all airports that require temperature corrections are listed in the notes section, and pilots should reference the FAA published list of airports whenever extremely cold temperatures exist at the destination airport. In the case of Laramie, the pilot would then consult the FAA list of airports requiring altimetry corrections to determine what segments of the approach should be corrected.
View the Complete List ofFAA Cold Temperature Restricted AirportsFor the Laramie approach, only the intermediate approach waypoints are required to be corrected. For Rawlins Municipal Airport the final approach waypoints are required to be corrected. The final approach waypoints are all the fixes located inside that final approach fix. i.e. The final approach fix, intermediate step-downs inside the FAF, and the MDA or DA(H).
When flight crewmembers make cold altimetry corrections in the intermediate approach and missed approachsegments,s they shall advise ATC so as to insure that ATC provides for adequate separation from other aircraft. The flight crew shall state, “Require XXXX altitude at HENSU for cold temperature operations”.
International Cold Temperature Restricted Airports
For international flight operations more research is required by the flight crew to determine the country specific requirements for cold altimetry procedures. General guidance, however, is provided in ICAO doc 8168 part 3 Chapter 4. Chapter 4 begins with the following note: “This chapter deals with altimeter corrections for pressure and temperature and, where appropriate, wind and terrain effects. The pilot is responsible for these corrections, except when under radar vectoring. In that case the radar controller issues clearances such that the prescribed obstacle clearance will exist at all times, taking the cold temperature correction into account.” For crewmembers operating internationally, they shall first evaluate country specific requirements for cold weather altimetry corrections and, if altimetry corrections are deemed necessary and prudent, they shall use the ICAO tabulated corrections and advise the controller prior to doing so.
FMS Cold Temperature Corrections
Some aircraft FMS’s are also capable of cold temperature corrections, the details of which are beyond the scope of this document. Crewmembers shall review their aircraft specific FMS to determine how and if automatic cold altimetry procedures shall be applied and if FMS cold temperature corrections are being applied, the crew must verify the system is on and operating prior to conducting a cold temperature augmented approach.
Revision date: July 29, 2015
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