The FAA’s Safety Tem has sent out a blast on the 2016 list of airports requiring Cold Weather Compensation. This Safety Tem blast is to be used with the procedure found in the Notices to Airmen, International/Domestic, Part 3, International Section. The new list and a new procedure go into effect 13OCT16.
What Has Not Changed
There is still a list of FAA identified airports that have instrument approaches loosing desired terrain and obstacle clearance in colder than standard temperatures. Pilots without an automatic “Temp Comp” feature in the FMC must use the previously published method of cold weather temperature compensation. This is now called the “Segments Method”.
Pilots using the “Segments Method” will need to reference the list of affected airports in the Notices to Airmen, International/Domestic, Part 3, International Section. From this list, pilots identify the critical temp and what specific instrument approach segments require a cold weather correction. Here are some more key point to remember using this method:
1. Only airports with a runway length of 2,500 feet or greater were evaluated
2. A critical temperature is identified that when, “at or below” , temperature compensation MUST be used on the identified approach segments
- 3. A “Snowflake icon” on the approach chart indicates there has been a critical temp and segment for this airport combination.
- 4. A manual calculation using the AIM 7-2-3, ICAO Cold Temperature Error Table is needed to determine the required add-on.
- 5. No extrapolation above the 5000ft column required. Pilots should use the 5000ft “height above airport in feet” column for calculating corrections of greater than 5000ft above reporting station.
- 6. ATC will require the pilot to report what altitude they are flying vice the published altitude.
Temperatures for Cold Temperature Restricted Airports are completely separate from the temperatures published on RNAV approaches. Temp restrictions on RNAV approaches for LP or LNAV/VNAV minima must be followed, even if it is warmer than the temperature associated with the “Snowflake” icon. In other words, “APPROACH NOT AUTHORIZED BELOW XX˚” is a separate calculation when using LNAV/VNAV or LP lines of minima.
Pilots must not correct altitudes published on Standard Instrument Departures, SIDs, Obstacle Departure Procedures, ODPs and Standard Terminal Arrivals, STARs.
ATC will not apply a cold temperature correction to radar vectoring altitudes. Pilots must be cleared by ATC to apply a cold temperature compensation to an ATC assigned altitude or when flying on a radar vector in lieu of a published missed approach procedure.
What Has Changed
FMC’s with “Temp Comp” available in your FMC the cold temp compensation procedure is somewhat more simplified. This is described as the “All Segments Method” Here are the items to remember:
- 1. Specifically look for a “Snowflake” icon and a cold weather compensation temperature limit on the approach chart. There is no need to reference the restricted airports list.
- 2. If below the Critical Temperature for Cold Weather Correction, pilots will select “Temp Comp” on the FMC and may correct all altitudes from the IAF altitude to the missed approach final holding altitude
- 3. ATC will require the pilot to report what altitude they are flying vice the published altitude.
When Using Either Cold Temperature Compensation Method
In another twist for this procedure in 2016, when using either the “All Segments” or “Segments” methods, pilots need to calculate the correction at the published MDA or DH/A and then add this to published altitude inside the Final Approach Fix (The FAF is included in the “All Segments” and “Segments” calculation already).
Here’s an example:
MDA = 7080ft
TDZE = 6606ft
Difference is (7080 – 6606) = 474ft
Use the table in AIM 7−2−3, find 474ft at −24C and the add-on correction is approximately 80ft. It is permissible to round up. In this case to 100 ft. Now add corrections to the MDA and any stepdown fix altitudes in final segment.
Here’s an example:
Published FAF Altitude = Do not Correct
Published Stepdown fix = 8400 + 80 = 8480ft
Published MDA = 7080 + 80 = 7160ft
Pilots still must meet the requirements in 14 CFR Part 91.175 in order to operate below the corrected MDA or DA. Pilots must see and avoid obstacles when descending below the MDA. You are correct if you think this procedure may increase your “Effective” descent minimums.