FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesMedium
A pilot on approach to a runway surrounded closely by hangars and trees experiences bumpy, irregular turbulence in the final 200 feet AGL. The atmosphere is stable with no convective activity present, but surface winds are gusty and moderate. This turbulence is most likely caused by
- AClear air turbulence from wind shear aloft
- BMechanical turbulence from surface obstructions
- CMountain wave turbulence
- DWake turbulence from a preceding aircraft
Show answer & explanationAnswer & explanation
Correct answer: B. Mechanical turbulence from surface obstructions
Mechanical turbulence results from wind flow being disrupted by friction from surface obstructions such as buildings and trees, creating irregular eddies near the ground independent of atmospheric instability.
Why the other options are wrong
- A. Clear air turbulence typically occurs at higher altitudes associated with wind shear, not near the surface from obstacles.
- C. Mountain wave turbulence requires significant terrain features and stable flow over mountains, not small surface obstructions.
- D. Wake turbulence is generated by wingtip vortices of another aircraft, not surface obstructions.
Mechanical Turbulence
Turbulence caused by wind flow disrupted by friction from surface obstructions such as buildings, trees, or rough terrain, creating irregular eddies.
- Occurs near the surface, independent of instability
- Increases with wind speed and surface roughness
- Common hazard on approach near buildings, trees, hangars
Memory trick: Wind hitting a building splashes into eddies — like water over rocks in a stream.