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Cold Temperature Altimeter Error

AIM ¶ 7-3-1 — Cold Temperature Altimeter Error

AIM 7-3-1 explains how cold temperatures cause barometric altimeters to read higher than true altitude. Study the ICAO error table for checkride prep.

In Plain English

Your barometric altimeter is calibrated to a standard atmosphere: 15°C at sea level, decreasing 2°C per 1,000 feet. When real-world temperatures don't match this standard, your indicated altitude and true altitude drift apart.

The key rule to remember: "From hot to cold, look out below."

  • When the ambient air is colder than standard, your true altitude is LOWER than what the altimeter shows. You're closer to the ground than indicated — a serious terrain and obstacle clearance hazard.
  • When the ambient air is warmer than standard, your true altitude is HIGHER than indicated.

For example, at 5,000 feet on a standard day, you'd expect about 5°C outside. If it's significantly colder, your altimeter is lying to you in the dangerous direction.

The ICAO Cold Temperature Error Table (TBL 7-3-1) lets you quantify the error. To use it:

  1. Find the reported temperature in the left column.
  2. Find the height above the airport (flight altitude minus airport elevation) across the top.
  3. The intersection shows how many feet you may be below your indicated altitude.

This matters most on instrument approaches in cold climates, where minimum altitudes provide tight obstacle clearance.

AIM Source Text
FAA AIM ¶ 7-3-1
7-3-1. 7-3-1. Effect of Cold Temperature on Barometric Altimeters Temperature has an effect on the accuracy of barometric altimeters, indicated altitude, and true altitude. The standard temperature at sea level is 15 degrees Celsius (59 degrees Fahrenheit). The temperature gradient from sea level is minus 2 degrees Celsius (3.6 degrees Fahrenheit) per 1,000 feet. For example, at 5000 feet above sea level, the ambient temperature on a standard day would be 5 degrees Celsius. When the ambient (at altitude) temperature is colder than standard, the aircraft's true altitude is lower than the indicated barometric altitude. When the ambient temperature is warmer than the standard day, the aircraft's true altitude is higher than the indicated barometric altitude. TBL 7-3-1 indicates how much error may exist when operating in non-standard cold temperatures. To use the table, find the reported temperature in the left column, and read across the top row to locate the height above the airport (subtract the airport elevation from the flight altitude). Find the intersection of the temperature row and height above airport column. This number represents how far the aircraft may be below the indicated altitude due to possible cold temperature induced error. TBL 7-3-1 ICAO Cold Temperature Error Table
Oral Exam Questions a DPE Might Ask
Q1What is the standard temperature and lapse rate used to calibrate barometric altimeters?
Per AIM 7-3-1, standard sea-level temperature is 15°C (59°F), with a lapse rate of -2°C (3.6°F) per 1,000 feet.
Q2If the outside air is colder than standard, is your true altitude higher or lower than indicated, and why does this matter?
Per AIM 7-3-1, when ambient temperature is colder than standard, true altitude is LOWER than indicated barometric altitude. This means the aircraft is closer to terrain and obstacles than the altimeter suggests — a serious safety concern, especially on approaches.
Q3How do you use the ICAO Cold Temperature Error Table in AIM 7-3-1?
Per AIM 7-3-1, find the reported temperature in the left column, then read across the top to find height above the airport (flight altitude minus airport elevation). The value at the intersection is how many feet the aircraft may be below the indicated altitude due to cold temperature error.
Related Paragraphs in AIM Chapter 7
7-3-2
Cold Temperature Altimeter Pre-Flight Planning
7-3-3
Cold Temperature Baro-VNAV Effects
7-3-4
Cold Temperature Airports
7-3-5
Cold Temperature Altitude Corrections
7-3-6
Cold Temperature Altitude Corrections
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AIM 7-3-1 — Cold Temperature Altimeter Error