IFH 5-6

Reported Temp C° Height Above Airport in Feet +10 0 -10 -20 -30 -40 -50 200 300 400 500 600 700 800 900 1,000 1,500 2,000 3,000 4,000 5,000 10 10 10 10 20 20 20 20 20 30 40 60 80 90 20 20 30 30 40 40 50 50 60 90 120 170 230 280 20 30 40 50 60 70 80 90 100 150 200 290 390 490 30 50 60 70 90 100 120 130 140 210 280 420 570 710 40 60 80 100 120 130 150 170 190 280 380 570 760 950 50 80 100 120 150 170 190 220 240 360 480 720 970 1,210 60 90 120 150 180 210 240 270 300 450 590 890 1,190 1,500 Figure 3-7. ICAO Cold Temperature Error. Figure 5-7. International Civil Aviation Organization (ICAO) cold temperature error table. (ICAO) standard formulas, shows how much error can exist when the temperature is extremely cold. To use the table, find the reported temperature in the left column, and then read across the top row to the height above the airport/reporting station. Subtract the airport elevation from the altitude of the final approach fix (FAF). The intersection of the column and row is the amount of possible error. Example: The reported temperature is –10 degrees Celsius (°C) and the FAF is 500 feet above the airport elevation. The reported current altimeter setting may place the aircraft as much as 50 feet below the altitude indicated by the altimeter. When using the cold temperature error table, the altitude error is proportional to both the height above the reporting station elevation and the temperature at the reporting station. For IFR approach procedures, the reporting station elevation is assumed to be airport elevation. It is important to understand that corrections are based upon the temperature at the reporting station, not the temperature observed at the aircraft’s current altitude and height above the reporting station and not the charted IFR altitude. To see how corrections are applied, note the following example: Airport Elevation 496 feet Airport Temperature –50 °C A charted IFR approach to the airport provides the following data: Minimum Procedure Turn Altitude 1,800 feet Minimum FAF Crossing Altitude 1,200 feet Straight-in Minimum Descent Altitude 800 feet Circling Minimum Descent Altitude (MDA) 1,000 feet The Minimum Procedure Turn Altitude of 1,800 feet is used as an example to demonstrate determination of the appropriate temperature correction. Typically, altitude values are rounded up to the nearest 100-foot level. The charted procedure turn altitude of 1,800 feet minus the airport elevation of 500 feet equals 1,300 feet. The altitude difference of 1,300 feet falls between the correction chart elevations of 1,000 feet and 1,500 feet. At the station temperature of –50 °C, the correction falls between 300 feet and 450 feet. Dividing the difference in compensation values by the difference in altitude above the airport gives the error value per foot. In this case, 150 feet divided by 500 feet = 0.33 feet for each additional foot of altitude above 1,000 feet. This provides a correction of 300 feet for the first 1,000 feet and an additional value of 0.33 times 300 feet, or 99 feet, which is rounded to 100 feet. 300 feet + 100 feet = total temperature correction of 400 feet. For the given conditions, correcting the charted value of 1,800 feet above MSL (equal to a height above the reporting station of 1,300 feet) requires the addition of 400 feet. Thus, when flying at an indicated altitude of 2,200 feet, the aircraft is actually flying a true altitude of 1,800 feet. Minimum Procedure Turn Altitude 1,800 feet charted = 2,200 feet corrected Minimum FAF Crossing Altitude 1,200 feet charted = 1,500 feet corrected Straight-in MDA 800 feet charted = 900 feet corrected Circling MDA 1,000 feet charted = 1,200 feet corrected Nonstandard Pressure on an Altimeter Maintaining a current altimeter setting is critical because the atmosphere pressure is not constant. That is, in one location the pressure might be higher than the pressure just a short distance away. Take an aircraft whose altimeter setting is set to 29.92" of local pressure. As the aircraft moves to an area of lower pressure (Point A to B in Figure 5-8) and the pilot fails to readjust the altimeter setting (essentially calibrating it to local pressure), then as the pressure decreases, the true altitude is lower. Adjusting the altimeter settings compensates for this. When the altimeter shows an indicated altitude of 5,000 feet, the true altitude at Point A (the height above