PHAK · Chapter 5: Aerodynamics of Flight
FAA · Retrieved 2026-09-05
Educational reference; original Owl summariesAERODYNAMICS
Mach number & compressibility
FLIGHT SCIENCE / CONCEPT REFERENCE
SCIENCEConditions & principles
The ratio of flow speed to the local speed of sound.
REFERENCE COVERAGE3 / 3 editorial sections
PROVENANCE1 linked source
LAST RETRIEVED2026-09-05
Editorial section coverage describes the article structure, not scientific validation or completeness.
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Source editions
PHAK · Chapter 5: Aerodynamics of Flight ↗Edition / snapshot: FAA-H-8083-25C, 2023Retrieved: 2026-09-05
Retrieval dates record when Owl obtained the data; they are not publication dates or proof that a specification is current. Where the edition contains only a snapshot date, the original publication date is not recorded.
01
Mechanism
Sound speed depends primarily on temperature in an ideal gas. Local acceleration over a wing can create sonic regions even when the aircraft’s free-stream Mach number is below one.
02
Aircraft response
Shock waves and compressibility can increase drag, alter pressure distribution and affect control or buffet boundaries.
03
Context & interpretation
Mach and true airspeed are not interchangeable. Local Mach number, geometry and lift coefficient influence the onset of transonic effects.
Physical relationship
M = V / a; a = √(γ R T)a: sound speed; γ: ratio of specific heats; T: absolute static temperature.
Sources & context
Educational explanation of physical mechanisms. Aircraft-specific procedures, limitations and current weather information are separate references.