Definition
A vibration or shaking of the airframe that occurs when an airplane approaches or exceeds its critical Mach number, caused by airflow over portions of the wing reaching supersonic speed and forming shock waves that disrupt the smooth flow of air over the wing surface.
Plain English
When a fast jet flies near the speed of sound, the air over its wings starts behaving in unstable ways and the airplane begins to shake. That shaking is called Mach buffet.
Context Anchor
Encountered in high-speed and high-altitude flight discussions, especially when learning about operating near an airplane’s maximum safe cruise speed.
Derivation
Mach comes from Ernst Mach, the physicist who studied the behavior of air at high speeds; a Mach number expresses speed as a fraction of the speed of sound. Buffet is an old word meaning to strike or shake repeatedly. Together the term names the shaking that happens when airflow over the wing starts to misbehave at speeds approaching the speed of sound.
Why Pilots Care
Mach buffet is an early warning that the aircraft is approaching its maximum operating speed; ignoring it can lead to loss of control or structural damage.
Grounding Statement
You can picture Mach buffet as smooth air over the airplane suddenly becoming disturbed at very high speed, making the airplane tremble.
Intuition Check
Buffet does not mean a meal here. In aviation, buffet means shaking or vibration caused by disturbed airflow.
Example Sentence 1
As the jet accelerated past its normal cruise speed, the crew felt the onset of Mach buffet and reduced thrust immediately.
Example Sentence 2
The training captain demonstrated Mach buffet by slowly increasing speed until the airframe began to shake.