Cold Temperature Restricted Airports

Cold Temperature Restricted Airports / Cold Temperature Altitude Corrections

Preface

This lesson is intended to explain the key elements of Cold Temperature Restricted Airports and Cold Temperature Altitude Corrections. You are encouraged to read the complete details, including useful examples, in the references listed below.

The Issue

Standard barometric altimeters are affected by temperature. Within a normal range of temperatures these errors are minimal, or in particularly hot temperatures, they can result in an altitude reading that is low thereby causing an aircraft (being flown at a particular indicated altitude) to be high with respect to the surface or obstacles.

But when when temperatures are very cold an altimeter will read high thereby causing an aircraft (being flown at a particular indicated altitude) to be low with respect to the surface or obstacles. This lower altitude can result in the aircraft unwittingly descending below a Require Obstacle Clearance (ROC) causing a possible safety of flight issue.

The FAA has analyzed US airports with Instrument Approach Procedures (IAPs), with runways of 2500 feet in length and longer, and has statistically determined those airports that present a potential safety risk in cold temperature operations. This list is updated regularly and is called the Cold Temperature Restricted Airports List. At these airports pilots must implement Cold Temperature Altitude Corrections when the operating temperature is at or below the stated temperature for that airport.

Pilots may optionally implement cold temperature corrections at other airports (such as those with runways of less than 2500 feet) but they must tell ATC if/when doing so.

References

Note that these references are currently in a state of flux (as of February, 2020) due to changes within the FAA with respect to how Cold Temperature Restricted Airports information is disseminated. Make sure to find and use the most recent information available since many changes have been instituted since the temperature correction procedure became mandatory for all pilots in September 2015.

1. Notices To Airmen Publication - NTAP, Aug 15, 2019 - The most current version of the relevant NTAP (as of February, 2020)
2. NBAA version/copy of Notices To Airmen Publication - NTAP, Aug 15, 2019 - A good link to the Aug 2019 document that might outlast the FAA link structure
3. Cold Temperature Restricted Airports List - This is just the list (but it is the official FAA list), but this link should always (hopefully) point to the current list.
4. AOPA - Cold Temperature Restricted Airports - A good overview of cold temperature airports/corrections, but only last updated in 2016
5. AIM, Chapter 7, Section 2. Altimeter Setting Procedures
6. Aeronautical Chart User’s Guide - Terminal Procedure Publications
7. Google Search for "Cold Temperature Restricted Airports" - useful if the other links above become invalid or outdated

Snowflake Icon on Instrument Approach Chart

Cold Temperature Restricted Airports are indicated on approach charts with a snowflake symbol in the notes section. Below are two images showing what the snowflake looks like in the notes section of the approach chart, and what the Aeronautical Chart User’s Guide - Terminal Procedure Publications says about the snowflake symbol and the approach:

The Correction Table

Corrections are made using a lookup table indexed by temperature and height above airport. The official table con be found in multiple places, including: AIM, Chapter 7, Section 2. Altimeter Setting Procedures, the NTAP, and the Aeronautical Chart User’s Guide - Terminal Procedure Publications. Below is a snapshot of the table as of February, 2020:

Is a Correction Needed?

If there is a published "snowflake" icon in the notes section of the approach chart, and the reported airport temperature is at or below the published temperature limit (next to the snowflake icon), then you must apply cold temperature altitude corrections.

Two Methods of Correction

There are two different ways to make cold temperature corrections, both are acceptable.

1. Make corrections for all segments of the approach from the Initial Approach Fix through the Missed Approach Hold. (Note that this method does not require access to the more detailed affected segment(s) information in the current NTAP and is therefore probably the most straight-forward method for most GA pilots.)
2. Make corrections only to the particular segments spelled out in the current NTAP publication. (Requires access to the current NTAP for detailed affected segment(s) information.)

In either case, you must notify ATC if/when making corrections to any segment other than the final approach segment.

How Corrections Are Made

Aircraft not equipped with a temperature compensating RNAV system or not using that system (use manual correction) should follow this procedure for the relevant segments (depending on which of the two methods, described above, are being used):

• All altitudes from the FAF/PFAF up to and including the IAF altitude: Calculate correction by taking FAF/PFAF altitude and subtracting the airport elevation. This number will be used to enter the height above airport in the ICAO table until reaching the reported temperature. Round this number as applicable and then add to all altitudes from the FAF altitude through the IAF altitude.
• All altitudes in final segment: Calculate correction by taking the MDA or DA for the approach being flown and subtract the airport elevation. This number will be used to enter the height above airport in the ICAO table until reaching the reported temperature. Use this number or round up. Add this number to MDA or DA/DH, as applicable, and any applicable step-down fixes in the final segment.
• Final holding altitude in the Missed Approach Segment: Calculate the correction by taking the final missed approach (MA) holding altitude and subtract the airport elevation. This number will be used to enter the height above airport in the ICAO table until reaching the reported temperature. Round this number as applicable and then add to the final MA altitude only.

Note that at no time should the pilot change the altimeter setting as part of the cold weather correction.

Detailed Examples

The best way to really understand the full process of making temperature corrections at a Cold temperature Restricted Airport is to run through a full example or two. And the best way to do that is to follow through the examples given in the NTAP (you may need to go to the full References section, above, if this link doesn't work or is out of date).

California Cold Temperature Restricted Airports

As of Aug, 2019, there are only 3 Cold Temperature Restricted Airports in California: Truckee (KTRK), Susanville (KSVE), and Nervino (O02). But note that this number can, and will, change from year to year due to the way the FAA continually evaluates airports for possible temperature restrictions.