What information does a Mach meter present?

What information does a Mach meter present?

• A. The ratio of aircraft indicated airspeed to the speed of sound.
• B. The ratio of aircraft true airspeed to the speed of sound.
• C. The ratio of aircraft equivalent airspeed, corrected for installation error, to the speed of sound.
• D. The ratio of wind speed to the speed of sound.

Answer: (B)

Mach number tells you how fast the airplane is moving relative to the speed of sound in the surrounding air. It’s the ratio of true airspeed to the local speed of sound, so the Mach meter displays a dimensionless value that depends on the air’s temperature (and thus altitude), not on density or wind directly. This is why pilots use Mach in high-speed flight: the speed of sound changes with temperature, so Mach provides a consistent measure of compressibility effects. For example, if the true airspeed equals the local speed of sound, the Mach readout is 1.0. Subsonic flight is below 1.0, and supersonic is above 1.0. Why the other ideas don’t fit: the Mach meter uses the ratio of true airspeed to the speed of sound, not indicated airspeed or equivalent airspeed. It isn’t a wind-to-sound ratio. Therefore the correct description is the ratio of true airspeed to the local speed of sound.

Mach number tells you how fast the airplane is moving relative to the speed of sound in the surrounding air. It’s the ratio of true airspeed to the local speed of sound, so the Mach meter displays a dimensionless value that depends on the air’s temperature (and thus altitude), not on density or wind directly. This is why pilots use Mach in high-speed flight: the speed of sound changes with temperature, so Mach provides a consistent measure of compressibility effects.

For example, if the true airspeed equals the local speed of sound, the Mach readout is 1.0. Subsonic flight is below 1.0, and supersonic is above 1.0.

Why the other ideas don’t fit: the Mach meter uses the ratio of true airspeed to the speed of sound, not indicated airspeed or equivalent airspeed. It isn’t a wind-to-sound ratio. Therefore the correct description is the ratio of true airspeed to the local speed of sound.