Special VFR, a closing daylight window and a fuel clock
You are pilot-in-command of a four-seat single-engine piston aeroplane on a VFR flight, 12 NM south of a Class D control-zone boundary at 2,500 ft, inbound to the zone aerodrome. Cruise is 110 kt; fuel remaining is 55 L and burn is 30 L/h; your planning final reserve is 45 minutes. The aerodrome reports ceiling 900 ft, visibility 6 km, trending TEMPO ceiling 700 ft, visibility 1,200 m in drizzle. Your State's AIP makes special VFR available in this control zone by day only, provided the reported ground visibility is at least 1,500 m and the ceiling at least 600 ft; the zone is flat, with nothing above 200 ft AGL within 5 NM of the field. Sunset is in 40 minutes. The only suitable alternate is 25 NM north, reporting ceiling 3,000 ft and visibility 10 km. ATC replies: 'Remain outside the control zone, expect special VFR, delay not determined.'
1. What do you calculate before accepting the hold, and what do you decide?
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Three clocks are running, and the holding instruction commits you to none of them.
Fuel. 55 L at 30 L/h is 110 minutes of endurance. Your 45-minute reserve is 22.5 L, so you have about 65 minutes of usable fuel. Inbound is 12 NM, roughly 7 minutes; the diversion to the northern alternate is 25 NM, roughly 14 minutes, plus 5 minutes for approach and landing. So the diversion costs about 20 minutes of the 65 available.
Daylight. Special VFR in this zone is a day-only privilege. Sunset is in 40 minutes, so any clearance that keeps you airborne past sunset is useless to you, and a night diversion into the alternate would be flown with the fuel margin already eaten into.
Weather. The TEMPO visibility of 1,200 m is below the 1,500 m minimum, so during those periods the clearance you are waiting for cannot legally be issued at all.
If ATC can put you inside the zone immediately, ask for it and accept. If the delay is undetermined, decline the hold: turn north now, in daylight, with full fuel margin, and divert. Orbiting outside a control zone while three independent windows close simultaneously is not a plan.
2. ATC then clears: 'Cleared to enter the control zone special VFR, maintain 1,500 ft, report field in sight.' What are your responsibilities under that clearance, and what would you query?
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A special VFR clearance is a VFR clearance, not an IFR clearance. It lets you enter controlled airspace below normal VFR weather minima; it does not authorise flight in cloud, and it does not transfer terrain or obstacle clearance to ATC.
Your obligations remain: remain clear of cloud, keep the surface in sight as required by the AIP, maintain the ground-visibility minimum, navigate by visual reference, and see and avoid other traffic. ATC provides separation from IFR traffic, but separation from other VFR aircraft is generally not assured, so the lookout stays entirely yours.
The 1,500 ft level must be queried. The reported ceiling is 900 ft. Whether ATC means 1,500 ft on the QNH or 1,500 ft AGL, that level is above the cloud base, so maintaining it would put you in cloud - precisely what special VFR does not permit. Ask for a level below the cloud with terrain and obstacle clearance assured, or tell ATC 'unable, request 1,000 ft' or similar. If no compliant level is offered, refuse the clearance and turn away while you still have the fuel and daylight to do so.
3. You enter the zone, but at 4 NM final the reported visibility drops to 1,200 m. What do you do and why?
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The clearance was issued against a reported ground visibility of at least 1,500 m. At 1,200 m the condition on which the clearance rests no longer exists, and continuing by default is not a decision - it is drift.
First, establish whether the field and its surface are in sight and whether you can keep a safe, obstacle-clear flight path clear of cloud. If you can, tell ATC the visibility has fallen below the minimum, and land at the aerodrome you are already committed to rather than turning back into the drizzle you came out of. Landing is the low-risk outcome; a rejected approach at 4 NM puts you back outside the zone with less fuel, less light and the same weather.
If you cannot keep the surface in sight or cannot stay clear of cloud, break off immediately, remain clear of the zone and return to the northern alternate. Set your own limit before you start: decide the point (for example 2 NM final) beyond which you land regardless, and do not renegotiate it because the field 'looks about the same'. Pushing on to minimums in special VFR is how controlled flight into terrain starts.