Cold temperature altitude correction
How much to add to each procedure altitude when the airport is colder than standard, by the ICAO equation, with the 4% rule and the ICAO table beside it.
Planning and education aid. Not for primary navigation. Full disclaimer
Experimental: not yet fully verified. How results are checked
Add 218 ft: fly 3,718 ft.
| Segment | Published altitude | Correction | Altitude to fly | 4% rule | From the table |
|---|---|---|---|---|---|
| FAF | 3,500 ft | 218 ft | 3,718 ft | 246 ft | 280 ft |
| MDA | 2,500 ft | 72 ft | 2,572 ft | 82 ft | 100 ft |
- Altitude to fly
- ISA deviation at the airport
Provenance
- Computed by
- aviation.altimetry.cold-temperature 1.0.0, core 0.1.0
- Model
- ΔH = (−ΔT_std ÷ L0) · ln(1 + L0·H ÷ (T0 + L0·H_aerodrome)), with L0 = −0.0019812 K/ft, T0 = 288.15 K, ΔT_std the airport temperature minus ISA at its elevation, and H the height above the airport (ICAO Doc 8168 Vol II, 2020; not the 2018 Vol III form). Approximations shown beside it: 4% of H per 10 °C below ISA, and AIM Table 7-3-1 read by bilinear interpolation
- Accuracy
- The equation is the ICAO standard for procedure design corrections. Transport Canada AC 500-020 (Issue 04, 2025) prints the same equation with T0 written as 273 + 15, which moves a correction by about 0.1 ft. The 4% rule and the table (built for a sea-level airport) run higher. Use the correction method your procedure and the FAA Cold Temperature Airports list in AIM 7-3 call for; this is a planning aid
- Notes
- 1 shown with the answer
- Cites
- International Civil Aviation Organization, Procedures for Air Navigation Services, Aircraft Operations (PANS-OPS), Doc 8168; Federal Aviation Administration, Aeronautical Information Manual
Something look off?
How we got thisFormula, worked example, sources, and proof
Model: ΔH = (−ΔT_std ÷ L0) · ln(1 + L0·H ÷ (T0 + L0·H_aerodrome)), with L0 = −0.0019812 K/ft, T0 = 288.15 K, ΔT_std the airport temperature minus ISA at its elevation, and H the height above the airport (ICAO Doc 8168 Vol II, 2020; not the 2018 Vol III form). Approximations shown beside it: 4% of H per 10 °C below ISA, and AIM Table 7-3-1 read by bilinear interpolation
Show your work
ISA deviation at the airport
-30 − 11.04= -41 °CCorrection for the first altitude
ΔH = (−ΔT ÷ L0) · ln(1 + L0·H ÷ (T0 + L0·H_aerodrome))(−-41 ÷ −0.0019812) · ln(1 − 0.0019812 × H ÷ (288.15 − 0.0019812 × 2,000))= 218 ft
The same steps an agent gets from the MCP server with explain: true.
Accuracy: The equation is the ICAO standard for procedure design corrections. Transport Canada AC 500-020 (Issue 04, 2025) prints the same equation with T0 written as 273 + 15, which moves a correction by about 0.1 ft. The 4% rule and the table (built for a sea-level airport) run higher. Use the correction method your procedure and the FAA Cold Temperature Airports list in AIM 7-3 call for; this is a planning aid
Worked example: A 2,000 ft airport at -30 °C, with a 3,500 ft final approach fix. Source: add-aviation-suite cold-temperature scenario: 1,500 ft above the airport at -30 °C corrects by about +218 ft, the 4% rule by about +246 ft.
You enter
- Procedure altitudes
- FAF, 3500 ft MDA, 2500 ft
- Airport elevation
- 2000 ft
- Reported airport temperature
- -30 °C
You get
- Correction to add
- 218 ft
- Altitude to fly
- 3,718 ft
- ISA deviation at the airport
- -41 °C
Review: Not yet independently reviewed by a flight instructor (CFI).
Last verified: 2026-09-23, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.
Status: version 1.0.0, core 0.1.0. See this tool in the verification report.
Checked against: 7 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.
Sources
- Procedures for Air Navigation Services, Aircraft Operations (PANS-OPS), Doc 8168, International Civil Aviation Organization, Volume II, 7th edition. Temperature correction of procedure altitudes below ISA (the 2020 equation, as cited in Transport Canada AC 500-020 section 4.8). Paid only.
- Aeronautical Information Manual, Federal Aviation Administration, Current edition. Chapter 7, Section 3 (cold temperature barometric altimeter errors, Table 7-3-1 ICAO Cold Temperature Error Table, and the Cold Temperature Airports list). Read free.
Terms
- ISA: International Standard Atmosphere
- A reference atmosphere: 15 °C and 1013.25 hPa at sea level, cooling 6.5 °C per kilometer up to 11 km. Altimeters and performance charts are built on it. Source: Manual of the ICAO Standard Atmosphere (Doc 7488)
Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.