Baro-VNAV temperature limit at Queenstown
You are flying an ATR 72 into NZQN. The RNAV (RNP) RWY 05 approach has LNAV/VNAV minima using Baro-VNAV. The chart note states that Baro-VNAV is not authorised below -5°C. The OAT is -8°C, QNH 1018, ceiling 600 ft, visibility 5 km. Your aircraft is approved for RNP APCH with Baro-VNAV but not RNP AR. You are cleared for the RNP approach. The GNSS receiver shows RAIM available. A NOTAM states that RNP AR is not available. You must decide which minima you can use, whether a temperature correction is needed, and what to do if the LNAV minima are not usable.
1. Can you fly the LNAV/VNAV minima? Explain.
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No. The chart note prohibits Baro-VNAV below -5°C and the OAT is -8°C. Baro-VNAV uses the barometric altimeter and is temperature-sensitive; cold temperatures cause the aircraft to be lower than indicated, so the vertical path is not assured. LNAV/VNAV is therefore not available. You may fly LNAV minima if the chart and your approval allow, using the MDA and step-down fixes, but you must not use the vertical guidance. Check whether the LNAV minima are usable with the reported visibility and whether the missed approach is compatible. If not, divert or hold for warmer conditions.
2. What about RNP AR? The NOTAM says RNP AR is not available.
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You are not approved for RNP AR and the NOTAM says it is not available, so RNP AR is not an option. RNP APCH is not the same as RNP AR; the 'AR' requires special aircraft and crew approval and obstacle analysis. Do not substitute the RNP AR chart. If the only usable minima are LNAV, confirm the aircraft is in LNAV mode, not LNAV/VNAV, and use the MDA. If the LNAV MDA is above the cloud base or visibility is insufficient, divert.
3. What temperature correction, if any, would you apply?
Read the worked answer
For LNAV only, apply cold-temperature corrections to the MDA and step-down altitudes if the chart requires. Use the aerodrome QNH and the chart's correction table or a computed correction; at -8°C the true altitude is lower than indicated, so add a correction. Do not apply a correction to the Baro-VNAV path because you are not using it. Cross-check the GNSS position and RAIM; RAIM is available, but that does not fix the temperature limit. If the corrected MDA leaves no margin, divert.