Cold Temperature Correction

What is Cold Temperature Correction?

Cold temperature correction is an upward adjustment applied to published instrument approach altitudes when the outside air temperature (OAT) is at or below 0°C. The correction ensures that an aircraft actually reaches the published minimum safe altitude, rather than flying lower than indicated by the altimeter.

When the air is much colder than standard, it is denser and the pressure gradient is steeper than the altimeter assumes. As a result, the aircraft is actually lower than the altimeter indicates — potentially by hundreds of feet on a very cold day at a high-elevation airport.

The practical consequence is significant: an aircraft flying what appears to be the published minimum descent altitude (MDA) or decision altitude (DA) may in reality be hundreds of feet below that value, placing it dangerously close to terrain or obstacles. Cold temperature correction adds the required buffer to keep the aircraft at the true, safe minimum altitude.

Cold temperature errors are greatest when:

• OAT is far below 0°C — the colder the temperature, the larger the error
• The altitude above the aerodrome is high — larger height differences amplify the error
• The aerodrome elevation is high — errors compound with greater height above the surface

Altitude Correction Table

The table below is used by pilots under FAA (AIM 7-2-3), Transport Canada (AIM RAC 9.18), and ICAO-aligned procedures. It gives the correction to add (in feet) based on your aerodrome temperature and height above the aerodrome elevation.

How to use it: Find the row matching your OAT, then find the column closest to the height above aerodrome for each altitude you need to correct. Add the correction to the published altitude and round up to the nearest 100 ft.

For temperatures between table rows, interpolate or use the colder row for a conservative result. Always round corrections up to the nearest 100 ft for published instrument approach procedures.

Step-by-Step Example

You are flying an ILS approach into an airport with the following conditions:

• Aerodrome elevation: 3,500 ft
• OAT: −25°C
• Published IAF altitude: 8,000 ft
• Published FAF altitude: 5,500 ft
• Published DA: 4,180 ft

Step 1 — Calculate height above aerodrome for each fix:

• IAF: 8,000 − 3,500 = 4,500 ft above aerodrome
• FAF: 5,500 − 3,500 = 2,000 ft above aerodrome
• DA: 4,180 − 3,500 = 680 ft above aerodrome

Step 2 — Look up corrections from the table at −25°C (interpolate between −20 and −30 rows):

• IAF (4,500 ft): interpolate between 570 and 760 at 4,000 ft → approximately 700 ft → round up to 800 ft
• FAF (2,000 ft): interpolate between 280 and 380 → approximately 330 ft → round up to 400 ft
• DA (680 ft): interpolate between 100 and 130 at 700 ft → approximately 115 ft → round up to 200 ft

Step 3 — Apply corrections:

• Corrected IAF: 8,000 + 800 = 8,800 ft
• Corrected FAF: 5,500 + 400 = 5,900 ft
• Corrected DA: 4,180 + 200 = 4,380 ft

Advise ATC of your corrected altitudes before commencing the approach.

When is Correction Required?

FAA (United States): Per FAA AIM 7-2-3 and AC 91-116, cold temperature corrections are required at Cold Temperature Restricted Airports (CTRAs) when OAT is at or below the published temperature restriction shown on the approach chart. At non-CTRA airports, pilots are encouraged to apply corrections whenever OAT is at or below 0°C. Corrections must be reported to ATC.

Transport Canada: Per TC AIM RAC 9.18, corrections are required at designated cold temperature airports when OAT is at or below the published threshold. The same altitude correction table is used.

Both authorities agree: corrections apply at or below 0°C, always add to the published altitude, and must always be rounded up. Never round down.

Frequently Asked Questions

Why does cold air make altimeters read high?

Your altimeter measures static pressure and converts it to altitude. Cold air is denser than standard, so the pressure at any given geometric altitude is higher than the altimeter model expects. The altimeter interprets this as a lower altitude — but the aircraft is actually even lower than that reading. The colder the air, the greater the error.

Do I apply the correction to all altitudes on the approach?

Yes — corrections should be applied to all altitude restrictions on the approach: IAF, IF, FAF, step-down fixes, DA, and MDA. Check your company procedures and applicable regulations for specific requirements.

Should I round up or down?

Always round up to the nearest 100 ft. Rounding down would result in flying below the corrected minimum, defeating the purpose of the correction. This calculator rounds up to the nearest 10 ft — you should then round that result up to the nearest 100 ft for published procedures.

Does the correction apply to SIDs and STARs?

Yes. Cold temperature corrections apply to any published minimum altitude, including departure procedures, SIDs, STARs, and crossing restrictions. Use the departure airport elevation as the aerodrome reference for departures, and the destination airport for arrivals.

What temperature do I use — surface or at altitude?

Use the surface temperature at the aerodrome as reported in the METAR or ATIS. You do not need a temperature reading at each fix altitude.

Do I need to tell ATC about my corrected altitudes?

Yes. When flying corrected altitudes that differ from published values, inform ATC so they can provide appropriate separation. A typical call: "Request to fly cold temperature corrected altitudes, [airport], OAT [X]°C." ATC will acknowledge and coordinate.