Airspeed Indicator Markings

The airspeed indicator restates the limitations in colour, so you can fly to them without recalling a number. Each arc has a lower and an upper end, and each end means something specific.

At a glance

• White arc40 to 85 KIAS
• Green arc48 to 129 KIAS
• Yellow arc129 to 163 KIAS
• Red line163 KIAS

Figure: Airspeed indicator markings (redrawn).

What each marking means

The arcs and the line

• White arc, 40 to 85 KIAS — the full flap operating range. Its lower limit is maximum weight V_S0 in the landing configuration; its upper limit is the maximum speed permissible with flaps extended.

• Green arc, 48 to 129 KIAS — the normal operating range. Its lower limit is maximum weight V_S1 at the most forward centre of gravity with flaps retracted; its upper limit is the maximum structural cruising speed.

• Yellow arc, 129 to 163 KIAS — fly here with caution, and only when the air is smooth.

• Red line, 163 KIAS — the maximum speed for all operations.

Why the two arcs start at different speeds

The white arc begins at 40 KIAS and the green at 48. Both lower ends are stalling speeds at maximum weight, but under different conditions: the white arc's is the landing configuration and the green arc's is flaps retracted at the most forward centre of gravity. Flaps lower the stalling speed, and the eight knot gap between the arcs is exactly that effect drawn on the dial.

The arcs overlap between 48 and 85 KIAS. In that band you are inside both the flap operating range and the normal operating range, which is why an approach with flaps out reads as ordinary on the dial.

Check yourself

• State the speed range of each arc and the red line speed.

• What does the lower end of the white arc represent, and in what configuration?

• What does the lower end of the green arc represent, and at what centre of gravity?

• Under what two conditions may the yellow arc be used?

• Why does the white arc start eight knots lower than the green arc?

Study aid — always fly your aircraft's current AFM/POH.