An RNAV (GPS) approach chart includes the note: 'Baro-VNAV NA below -15°C (5°F).' The current reported temperature at the airport is -20°C. How does this affect the approach the pilot may fly?
- AThe approach may not be flown at all under any minimums due to the cold temperature restriction
- BThe LNAV/VNAV minimums may not be used; the pilot must fly to the LNAV (or circling) minimums using an MDA instead of a DA
- CThe restriction only applies to Category C and D aircraft; smaller aircraft may disregard the temperature note
- DThe pilot may still use LNAV/VNAV minimums but must add 100 feet to the DA to compensate for cold temperature error
Show answer & explanationAnswer & explanation
Correct answer: B. The LNAV/VNAV minimums may not be used; the pilot must fly to the LNAV (or circling) minimums using an MDA instead of a DA
Baro-VNAV systems compute vertical guidance based on standard atmosphere assumptions, and extremely cold temperatures cause the computed glidepath to be lower than the charted glidepath, creating an obstacle clearance hazard. When the temperature is below the charted limit, the pilot must not use LNAV/VNAV minimums and instead fly the approach to LNAV (MDA-based) or circling minimums, which are not affected by temperature-induced vertical errors.
Why the other options are wrong
- A. Incorrect — the approach may still be flown using LNAV or circling minimums
- C. Incorrect — the temperature restriction applies to all aircraft using Baro-VNAV, regardless of category
- D. Incorrect — no such 100-foot correction procedure exists; the correct action is to change minima lines
Baro-VNAV Cold Temperature Restriction
A chart note restricting Baro-VNAV (LNAV/VNAV) use below a specified temperature because cold air causes the computed vertical path to fly lower than intended, requiring pilots to use LNAV or circling minimums instead.
- Cold temperatures cause true altitude to be lower than indicated altitude
- Restriction is charted as 'Baro-VNAV NA below [temp]'
- Below the limit, use LNAV (MDA) minimums instead of LNAV/VNAV (DA) minimums
Memory trick: Cold air lies low — below limit, drop VNAV, fly LNAV.