FAA Private Pilot Helicopter (PRH)WeatherMedium
A pilot decoding a Winds and Temperatures Aloft Forecast (FD) for the 3,000-foot level finds the coded group '9900'. This coded group means
- AWind from 090° at 90 knots with no temperature forecast
- BLight and variable wind less than 5 knots, with no temperature forecast
- CData is missing for this altitude and station
- DWind from 099° at 0 knots, calm
Show answer & explanationAnswer & explanation
Correct answer: B. Light and variable wind less than 5 knots, with no temperature forecast
The special code '9900' in an FD forecast indicates light and variable wind of less than 5 knots. Temperatures are not forecast for levels within 2,500 feet of station elevation, which is why no temperature appears in this group.
Why the other options are wrong
- A. 9900 is a reserved special code, not a literal direction/speed decode.
- C. 9900 is a valid forecast code, not an indication of missing data.
- D. This misreads the digit groupings; 9900 is not decoded as a normal direction/speed pair.
Winds Aloft Forecast Coding
FD forecasts encode wind direction (tens of degrees true), speed (knots), and temperature (°C) in six-digit groups, with special codes for light/variable conditions and high altitudes.
- '9900' = light and variable wind, less than 5 knots
- Temperature omitted within 2,500 ft of station elevation
- Above 24,000 ft, add 50 to direction code and 100 to speed to distinguish high-speed winds
Memory trick: '99 means 99 problems but wind ain't one—light and variable'