Airspeed and altitude for navigation

Navigation reduces to track, heading, time and fuel, and every one of those depends on knowing two things accurately: how fast the aeroplane is actually moving through the air, and how high it is. Get the speed wrong and your timing and fuel are wrong. Get the altitude wrong and you risk the ground, controlled airspace above you, or a performance figure that does not match reality. This section ties both together for navigation use. Meteorology covers the physics of the standard atmosphere and altimetry in depth; here we focus on the numbers you feed into a flight log.