ATPL - The Mach number:

Question id 156 - Principles of Flight - ATPL - Airline Transport Pilot license

Is the ratio between the TAS of the aeroplane and the speed of sound at sea level.

Is the ratio between the IAS of the aeroplane and the local speed of sound.

Is the ratio between the TAS of the aeroplane and the local speed of sound.

Increases at a given TAS, when the temperature rises.