FAA Part 107 Remote Pilot (UAG)WeatherHard
A remote pilot launches a small UA immediately downwind of a row of large hangars during a period of moderate surface winds. Shortly after takeoff, the aircraft experiences sudden, erratic bumps and abrupt altitude changes. What is the most likely cause of this turbulence?
- AFrontal turbulence from an approaching cold front
- BMechanical turbulence caused by wind flowing over and around obstructions
- CClear air turbulence associated with the jet stream
- DWake turbulence from a departing manned aircraft
Show answer & explanationAnswer & explanation
Correct answer: B. Mechanical turbulence caused by wind flowing over and around obstructions
Mechanical turbulence occurs when wind flows over or around obstructions such as buildings, hangars, or trees, creating rotors and eddies on the downwind side. This effect is strongest close to the ground near large structures, exactly as described in the scenario.
Why the other options are wrong
- A. No frontal passage is described; frontal turbulence would be tied to a specific approaching front, not obstructions.
- C. Clear air turbulence occurs at high altitudes near jet streams, far above sUAS operating altitudes.
- D. No manned aircraft departure is mentioned; wake turbulence comes from wingtip vortices of another aircraft.
Mechanical Turbulence
Turbulence caused by wind flow being disrupted as it passes over or around surface obstructions like buildings, trees, or terrain.
- Strongest immediately downwind of the obstruction
- Increases with wind speed and obstruction height
- Can create rotors and sudden altitude/attitude changes for sUAS
Memory trick: 'Mechanical = Machines and buildings mechanically chop the wind into eddies.'