One gauge tells the pilot whether the wing is still flying. The airspeed indicator compares ram air pressure from the pitot tube against static pressure from a port on the fuselage. The difference drives a needle across a dial marked with colour-coded ranges.

Green means normal operating range. Yellow marks caution. Red marks never-exceed speed. White shows the flap operating range. Pilots learn these arcs before they ever solo, because crossing the wrong line can mean structural failure or an unexpected stall.

Common failure modes

• Blocked pitot tube from ice or insects
• Blocked static port from debris
• Leaking pressure lines
• Instrument mechanical failure

Pilots cross-check other instruments when airspeed readings seem wrong. A pitot blockage during climb can make the indicator read like a descent, which has caused fatal accidents.