VFR to Kumasi with a Squall Line Building
You are planning a VFR flight from Accra (DGAA) to Kumasi, 110 nm, in a Cessna 172, departing 15:20 with an ETA of 16:05 and a planned return at 17:00. It is late April. The 11:00 UTC TAF for Accra reads: 22012KT 9999 SCT025 TEMPO 1415/1419 24018G35KT 3000 TSRA BKN012 FEW025CB BECMG 1420/1422 24006KT 9999 SCT020. Kumasi has no current METAR because its automatic station is unserviceable; a pilot who has just landed there reports a line of cumulonimbus 20 nm west of the route, tops above FL350, with heavy rain reaching the ground, the line moving east-northeast at 15 kt. Fuel on board allows 3 h 10 min endurance; you have no instrument rating and the aircraft has no weather radar. Your dispatcher says it is VFR now, so just go.
1. Decode the TEMPO group and explain what it means for your flight window.
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The TAF is valid from day 14 at 12:00 to day 15 at 18:00 UTC (Ghana keeps GMT, so UTC equals local time).
Base conditions: wind 220°/12 kt, visibility 10 km or more, scattered cloud at 2,500 ft.
TEMPO 1415/1419 = between 15:00 and 19:00 on the 14th, temporary fluctuations from the base conditions are forecast. 'TEMPO' means the conditions may occur for periods generally of less than an hour at a time, but within that four-hour window they are expected at some point - not a one-off possibility.
Inside the window: wind 240°/18 kt gusting 35 kt, visibility 3,000 m, thunderstorm with rain, broken cloud at 1,200 ft and a few cumulonimbus at 2,500 ft.
BECMG 1420/1422: a gradual, permanent change back to 240°/6 kt, 10 km, scattered at 2,000 ft from between 20:00 and 22:00.
Your departure at 15:20 and return at 17:00 sit squarely inside the TEMPO window, and the ceiling of 1,200 ft with 3,000 m visibility is below VFR minima - so the group is not academic, it describes the flight you are proposing to make.
2. Is a VFR departure to Kumasi acceptable? What alternate and fuel planning does this require?
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No - not on this evidence. The reasoning chain:
- No destination forecast or observation. Kumasi has no TAF and no METAR. You would be departing towards a destination whose weather is unknown, with no instrument capability to get in if it is below VFR minima.
- A pilot report of an active CB line 20 nm from the route, tops above FL350, moving east-northeast at 15 kt - towards the route, not away from it.
- A TEMPO group that breaks VFR minima at the departure aerodrome during your entire planned window.
- No alternate weather to plan against. For a VFR flight you must still be able to reach a suitable aerodrome with weather at or above VFR minima at ETA ±1 hour; you cannot name one today.
VFR in controlled airspace follows ICAO minima: 5 km visibility below 10,000 ft (8 km at or above), 1,500 m horizontally and 1,000 ft vertically from cloud. A cumulonimbus at 2,500 ft in the departure area breaches the cloud-clearance rule by itself.
The correct decision is to delay to after 19:00, depart earlier with a firm return before 15:00, or cancel and travel by road. Fuel that allows 3 h 10 min is adequate in time but irrelevant if there is nowhere to divert to.
3. You are airborne and 15 nm ahead a wall of cloud reaches the ground with heavy rain. What do you do?
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Read it as a downburst, not as rain. Heavy rain reaching the ground under a CB means a descending downdraught with an outflow boundary - the classic microburst signature: sudden wind shift, airspeed spike then collapse, and no ability to out-climb it at 172 performance.
Actions, in order:
- Turn 180° immediately and clear the cell by at least 20 nm. Do not attempt to top it (tops above FL350), do not scud-run beneath it, and do not try to find a gap - the line is moving towards you.
- Maintain terrain awareness during the turn; in the Accra–Kumasi corridor there is high ground to the southeast of the direct track.
- Advise ATC of the position and extent of the cell - other traffic is behind you.
- Re-plan: return to Accra, or divert to the nearest aerodrome with reported conditions at or above VFR minima, and check fuel against the new destination.
- If the aircraft is inadvertently caught, prioritise: attitude, full power, do not chase the airspeed indicator, accept the altitude loss, and report.
After landing, file the encounter. A dispatcher's 'it is VFR now' is not a meteorological argument, and that pressure is exactly what the report should document.