FAA Aircraft Dispatcher (ADX)MeteorologyMedium
A dispatcher is decoding a winds aloft forecast (FD) for FL390 and reads the coded group '731960'. What are the forecast wind direction, speed, and temperature?
- A073° at 19 knots, -60°C
- B230° at 119 knots, -60°C
- C073° at 119 knots, +60°C
- D230° at 19 knots, -160°C
Show answer & explanationAnswer & explanation
Correct answer: B. 230° at 119 knots, -60°C
For forecast winds of 100 knots or greater, 50 is added to the direction (first two digits) and 100 is subtracted from the speed (next two digits) when coding. To decode '731960': direction = 73-50=23, so 230°; speed = 19+100=119 knots; temperature = -60°C (temperatures above 24,000 ft are always negative and the sign is omitted).
Why the other options are wrong
- A. This ignores the coding convention requiring subtraction of 50 from the direction and addition of 100 to the speed.
- C. The temperature sign is always negative above 24,000 ft, not positive, and speed is misread.
- D. The temperature would be an impossible -160°C; only the tens/units of temperature are coded, not a triple digit value.
Winds Aloft Forecast (FD) Coding
A coded 6-digit group representing forecast wind direction, speed, and temperature at a given altitude, with special coding for winds ≥100 knots.
- First 2 digits = wind direction (tens of degrees); add 50 if ≥100kt coded
- Middle 2 digits = wind speed in knots; subtract 100 if direction was coded +50
- Last 2 digits = temperature in °C; always negative above 24,000 ft (sign omitted)
Memory trick: Add 50, sub 100 — that's the code when winds are fast and hot to trot (fast, that is).