The ASI has colour markings indicating critical speed limits. Defined in CS-23.1545 and in the AFM/POH of each type.
Colour code
| Marking | Speed range | Meaning |
|---|---|---|
| White arc | Vs0 to Vfe | Flap operating range. Lower limit = stall in landing config, upper = max flap speed |
| Green arc | Vs1 to Vno | Normal operating range. Lower = stall in clean config, upper = max structural cruising |
| Yellow arc | Vno to Vne | Caution range. Smooth air only |
| Red line | Vne | Never Exceed — never exceed |
V-speeds
ASI arc markings with V-speeds. Values are examples for a C172. (selection)
| Symbol | Meaning |
|---|---|
| Vs0 | Stall speed in landing config (full flaps, gear down) |
| Vs1 | Stall speed in clean config |
| Vfe | Max flap extension speed |
| Vno | Max structural cruising speed |
| Vne | Never exceed |
| Va | Manoeuvring speed (often not a marking; in AFM limits) |
| Vx | Best angle-of-climb speed |
| Vy | Best rate-of-climb speed |
| Vr | Rotation speed on take-off |
Va — special role
Va is the speed at which full deflection of a control will stall the wing before structural limit load is reached. Va decreases with reducing mass — a lighter aircraft has a lower Va.
In turbulence, it is recommended not to exceed Va — to protect the structure from gust loading.