Effects of Cold Temperature on Baro-Vertical…

AIM Text

Non-standard temperatures can result in a change to effective vertical paths and actual descent rates when using aircraft baro-VNAV equipment for vertical guidance on final approach segments. A lower than standard temperature will result in a shallower descent angle and reduced descent rate. Conversely, a higher than standard temperature will result in a steeper angle and increased descent rate. Pilots should consider potential consequences of these effects on approach minima, power settings, sight picture, visual cues, etc., especially for high-altitude or terrain-challenged locations and during low-visibility conditions.

Uncompensated Baro-VNAV note on 14 CFR part 97 IAPs. The area navigation (RNAV) global positioning system (GPS) and RNAV required navigation performance (RNP) notes, “For uncompensated Baro-VNAV systems, lateral navigation (LNAV)/VNAV NA below –XX°C (-XX°F) or above XX°C (XXX°F)” and “For uncompensated Baro-VNAV systems, procedure NA below –XX°C (-XX°F) or above XX°C (XXX°F)” apply to baro-VNAV equipped aircraft. These temperatures and how they are used are independent of the temperature and procedures applied for a Cold Temperature Airport.
1. The uncompensated baro-VNAV chart note and temperature range on an RNAV (GPS) approach is applicable to the LNAV/VNAV line of minima. Baro-VNAV equipped aircraft without a temperature compensating system may not use the RNAV (GPS) approach LNAV/VNAV line of minima when the actual temperature is above or below the charted temperature range.
2. The uncompensated baro-VNAV chart note and temperature range on an RNAV (RNP) approach applies to the entire procedure. For aircraft without a baro-VNAV and temperature compensating system, the RNAV (RNP) approach is not authorized when the actual temperature is above or below the charted uncompensated baro-VNAV temperature range.
Baro-VNAV temperature range versus CTA temperature: The baro-VNAV and CTA temperatures are independent and do not follow the same correction or reporting procedures. However, there are times when both procedures, each according to its associated temperature, should be accomplished on the approach.
Operating and ATC reporting procedures.
1. Do not use the CTA operating or reporting procedure found in this section, 7-3-4 a thru 7-3-5 e when complying with the baro-VNAV temperature note on an RNAV (GPS) approach. Correction is not required nor expected to be applied to procedure altitudes or VNAV paths outside of the final approach segment.
2. Operators must advise ATC when making temperature corrections on RNP authorization required (AR) approaches while adhering to baro-VNAV temperature note.
3. Reporting altitude corrections is required when complying with CTAs in conjunction with the baro-VNAV temperature note. The CTA altitude corrections will be reported in this situation. No altitude correction reporting is required in the final segment.
  
  NOTE-
  
  When executing an approach with vertical guidance at a CTA (i.e., ILS, localizer performance with vertical guidance (LPV), LNAV/VNAV), pilots are reminded to intersect the glideslope/glidepath at the corrected intermediate altitude (if applicable) and follow the published glideslope/glidepath to the corrected minima. The ILS glideslope and WAAS generated glidepath are unaffected by cold temperatures and provide vertical guidance to the corrected DA. Begin descent on the ILS glideslope or WAAS generated glidepath when directed by aircraft instrumentation. Temperature affects the precise final approach fix (PFAF) true altitude where a baro-VNAV generated glidepath begins. The PFAF altitude must be corrected when below the CTA temperature restriction for the intermediate segment or outside of the baro-VNAV temperature restriction when using the LNAV/VNAV line of minima to the corrected DA.

Source: FAA Aeronautical Information Manual · current edition · paragraph 7-3-3.

The short answer

AIM 7-3-3 is FAA advisory guidance on how non-standard cold temperatures affect baro-VNAV vertical guidance on final approach. Colder-than-standard air produces a shallower descent angle and reduced rate; warmer air a steeper angle. It also explains uncompensated baro-VNAV chart notes and Cold Temperature Airport procedures supporting 14 CFR 91.121 and 14 CFR 91.175.

Research Notes

Common Questions

How does cold temperature change my descent angle on a baro-VNAV approach?

AIM 7-3-3 states a lower-than-standard temperature results in a shallower descent angle and reduced descent rate, while a higher-than-standard temperature produces a steeper angle and increased descent rate. Pilots should consider the effects on approach minima, power settings, sight picture, and visual cues.

Do I change my altimeter setting to make a cold temperature altitude correction?

No. AIM 7-3-5 (covered here) states pilots must not make an altimeter change to accomplish an altitude correction; the altimeter must be set to the current setting provided by ATC per 14 CFR 91.121. Corrections are added to published segment altitudes instead.

When must I report a cold temperature altitude correction to ATC?

Per the Cold Temperature Airport procedures in AIM 7-3-3, pilots must advise ATC with the corrected altitude on any approach segment except the final segment, and must request ATC approval before applying a correction to any ATC-assigned altitude, MVA, or MIA.

7-3-3. Effects of Cold Temperature on Baro-Vertical Navigation (VNAV) Vertical Guidance