Buffeting in cruise that is difficult to identify could be caused by which combination of speeds?

• A. Either low speed buffeting or high speed buffet
• B. Only low speed buffet
• C. Only high speed buffet
• D. No buffet at cruise

Answer: (A)

Buffeting at cruise can come from two different flow regimes, depending on how fast you’re flying. There are two well-known kinds: one happens when the airplane is near its stall at relatively lower speeds, where the wing or tail can experience separated flow and turbulent pressure fluctuations. The other happens at higher, transonic speeds when shock waves form and cause flow separation, leading to a separate kind of buffet often called Mach or high-speed buffet.

In cruise, you might be operating in a regime where either of these mechanisms could be present, depending on weight, altitude, configuration, and thrust. Because the same or similar vibrations can result from these distinct flow phenomena, the source isn’t always easy to pinpoint. That’s why the observed buffet in cruise can be caused by either low-speed buffet or high-speed buffet—the combination of speeds that could lead to buffet isn’t limited to one end of the spectrum.