Rotorua Charter: TAF TEMPO Below Company Minima
You are the pilot-in-command of a Part 135 IFR charter from Auckland (NZAA) to Rotorua (NZRO), ETD 1000 UTC, ETA 1045 UTC, carrying six passengers. The 0600 UTC TAF is: NZRO 020600Z 0207/0307 21012KT 9999 -SHRA SCT018 BKN030 TEMPO 0208/0214 20015G25KT 2000 +SHRA BKN006 FEW020CB BECMG 0210/0212 20008KT. Company destination minima for NZRO are 600 ft ceiling and 3 km visibility. The North Island GAFS for the same period shows a trough over the central plateau with isolated embedded CB tops FL280, moderate turbulence below FL120 and localised heavy showers. The aircraft has serviceable weather radar. The only suitable alternate with a current TAF is Hamilton (NZHN), 25 minutes away, whose TAF is fine. Your fuel plan includes 30 minutes holding at destination plus 45 minutes reserve.
1. Decode the TAF change groups and state the worst credible conditions at your ETA. Does the destination forecast meet company minima?
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The TAF base group 0207/0307 gives 21012KT, 9999, -SHRA, SCT018 BKN030. The TEMPO group 0208/0214 gives 20015G25KT, 2000 m visibility, +SHRA, BKN006 and FEW020CB. The BECMG 0210/0212 changes the wind to 20008KT. Your ETA 1045 UTC falls inside the TEMPO period. Worst credible conditions at ETA are therefore: visibility 2000 m, ceiling 600 ft, heavy showers, CB cloud and gusts to 25 kt. Company minima are 600 ft ceiling and 3 km visibility. The ceiling is exactly at the 600 ft limit, but the visibility of 2000 m is below the 3 km requirement. A TEMPO group is a temporary fluctuation, not a guarantee, but it is part of the forecast and must be treated as credible for planning. On this TAF the destination does not meet company minima at ETA unless an amended TAF removes or raises the TEMPO conditions.
2. Using the TAF and GAFS together, decide whether an alternate is required and whether the CB risk changes your route or fuel plan.
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Because the TEMPO puts NZRO below company minima at ETA, an alternate is required. NZHN has a current TAF and is only 25 minutes away, so it can satisfy the alternate forecast and fuel requirement. The GAFS does not override the TAF: it adds isolated embedded CB tops FL280, moderate turbulence below FL120 and localised heavy showers. With serviceable radar, I would route to keep a safe lateral buffer from the CB line, avoid penetration of embedded CB, and expect deviations. The existing 30 minutes holding plus 45 minutes reserve is only adequate if fuel to NZHN as alternate plus reserve is confirmed. If the CB line is more extensive than the GAFS suggests, I would delay or nominate NZHN as the destination rather than press into NZRO.
3. What would you tell dispatch, and which later product would cause you to re-plan?
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I would tell dispatch that the 0600 TAF puts NZRO below company minima in the TEMPO group at ETA, so I am nominating NZHN as alternate, requesting fuel to NZHN plus reserve, and asking for the latest TAF and any SPECI before departure. I would re-plan if: an amended TAF removes the TEMPO or lifts conditions above 600 ft and 3 km; a SPECI at NZRO reports ceiling below 600 ft or visibility below 3 km; a SIGMET is issued for embedded CB or severe turbulence; or airborne radar shows a continuous CB line that cannot be avoided with a safe buffer. An AIRMET for moderate turbulence would not by itself stop the flight, but it would affect ride quality, route selection and passenger briefing.