What it is: The reading comes from the pitot-static system rather than GPS or groundspeed, so it reflects how the aircraft is moving through the air around it. Because of that, IAS is the figure used for most speed limits, flap and gear operation, climb and approach targets, and stall awareness in the cockpit.
In practice: During a simulated flight, you will usually fly by IAS rather than groundspeed. Rotation, climb-out, approach and final are all flown to indicated speeds taken from the aircraft handbook, checklists or onboard references. As altitude increases, true airspeed rises while IAS for the same aerodynamic condition stays lower, which is why a jet can show a modest IAS at cruise yet cover ground quickly. Wind also changes groundspeed without changing IAS directly, so a strong headwind may slow your progress while the aircraft still flies the correct approach speed.
Key considerations:
- Use IAS for take-off, climb, approach and landing targets unless the aircraft specifically calls for another reference such as Mach.
- Do not confuse IAS with groundspeed: navigation timing and arrival estimates depend on groundspeed, but aircraft handling depends mainly on IAS.
- If the pitot-static system is modelled accurately and becomes blocked or fails, the IAS indication can become unreliable.
