Buffet at cruise speed can be difficult to identify because it may be produced by:

• A. Weather only
• B. Low speed buffet only
• C. High speed buffet only
• D. Either low speed buffet or high speed buffet

Answer: (D)

Buffet at cruise speed can be produced by both low-speed and high-speed mechanisms, so the source isn’t confined to one cause. Low-speed buffet happens when the wing’s lift is high enough to cause flow separation and turbulent wake, often near stall or with certain flap configurations, leading to unsteady pressures and vibrations. High-speed buffet shows up in the transonic range, where shock waves form and move, causing boundary-layer separation and rapid, unsteady airflow that also produces buffet and control feel. At cruise, especially on airliners, you can be near conditions where either mechanism may be at play, and the visible symptoms can be similar, making the exact source hard to identify from sensation alone.