Definition
A published restriction prohibiting the use of Barometric Vertical Navigation (Baro-VNAV) for the vertical guidance portion of an instrument approach when the airport temperature is below (or, in some cases, above) the values stated on the approach chart. Baro-VNAV derives its glidepath from barometric altitude, which becomes inaccurate in non-standard temperatures: in very cold air the actual glidepath flies lower than indicated, and in very hot air it flies higher. The charted temperature limits define the range within which the system's vertical guidance remains safe to use without correction.
Plain English
Baro-VNAV builds its descent path using pressure altitude, and that path drifts when the air is much colder or hotter than standard. Each approach chart lists a minimum (and sometimes maximum) temperature. If the actual temperature is outside that range, you cannot use Baro-VNAV to fly the descent on that approach.
Context Anchor
Seen in the notes or limitations for instrument approach procedures that use Baro-VNAV vertical guidance, especially approaches with LNAV/VNAV minimums.
Derivation
Baro' is short for barometric, from Greek 'baros' meaning weight, referring to the weight of the atmosphere measured by a pressure-sensing altimeter. 'VNAV' stands for vertical navigation. The term tells you the system is using air pressure to build its vertical path, which is exactly why temperature affects it: cold air is denser, so a given pressure occurs at a lower true altitude than the altimeter shows.
Why Pilots Care
Using Baro-VNAV outside the published temperature range can place the aircraft lower than the published glidepath, reducing obstacle clearance margins.
Grounding Statement
In cold air, your altimeter reads higher than you actually are, so a glidepath calculated from that altimeter sits lower than it should -- the temperature limit is the line at which that error becomes unsafe.
Intuition Check
Do not read “temperature limitation” as a comfort limit or a general engine-weather limit. Here it means a published airport temperature range for using pressure-based vertical approach guidance safely.
Example Sentence 1
The reported temperature was minus twenty-two Celsius, three degrees below the Baro-VNAV temperature limitation on the chart, so the crew briefed the LNAV minimums instead of LNAV/VNAV.
Example Sentence 2
When the surface temperature fell below the published Baro-VNAV temperature limitation, the crew switched to the ILS for vertical guidance.