Airspeed Indicator Markings

The airspeed indicator carries the limitations table in colour. Four markings, and each arc's two ends are themselves limitations you have already met in numeric form.

At a glance

• White arc (full flap operating range)35 to 85 KIAS
• Green arc (normal operating range)40 to 111 KIAS
• Yellow arc (caution range)111 to 149 KIAS
• Red line (maximum for all operations)149 KIAS

Figure: Airspeed indicator markings (redrawn).

What each arc's ends mean

The white arc, 35 to 85 KIAS

• Lower limit, 35 KIAS — maximum weight V_S0, the stalling speed in the landing configuration.

• Upper limit, 85 KIAS — the maximum speed permissible with flaps extended.

• Significance — the full flap operating range.

The green arc, 40 to 111 KIAS

• Lower limit, 40 KIAS — maximum weight V_S at the most forward centre of gravity, with flaps retracted.

• Upper limit, 111 KIAS — the maximum structural cruising speed.

• Significance — the normal operating range.

The two arcs begin at different speeds because they describe two different stalls. Flaps down the aeroplane stalls at 35 knots; flaps up and at the most forward centre of gravity it stalls at 40. That five-knot gap is the whole reason the white arc extends below the green.

Caution and prohibition

The yellow arc runs from 111 to 149 KIAS, and flying inside it calls for caution and demands smooth air. The red line sits at 149 KIAS and marks the maximum speed for all operations.

Reading across from the numeric limitations: the yellow arc starts where V_NO ends and finishes where V_NE begins. The colours and the numbers are two presentations of one set of limits.

Check yourself

• What speed does the white arc begin at, and what does that lower limit represent?

• What does the upper end of the green arc correspond to?

• Why do the white and green arcs start at different speeds?

• What is the operating rule for the yellow arc, and where does the red line sit?

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