Airspeed Limitations

These are the FAA approved speed limits — the ones that bound the aeroplane structurally rather than advise you about comfort. Each is published twice, in calibrated and in indicated knots, and the indicated figure is the one you fly to.

At a glance

• Type CertificateNo. 3A12
• V_NE, never exceed160 KCAS / 163 KIAS
• V_NO, maximum structural cruising126 KCAS / 129 KIAS
• V_A at 2550 lb102 KCAS / 105 KIAS
• V_A at 2200 lb95 KCAS / 98 KIAS
• V_A at 1900 lb88 KCAS / 90 KIAS
• V_FE with 10° flap107 KCAS / 110 KIAS
• V_FE, 10° to 30° flap85 KCAS / 85 KIAS
• Maximum window open speed160 KCAS / 163 KIAS
• Utility category V_A at 2200 lb98 KIAS

Which static source the figures assume

The airspeeds in the limitations chart and in the airspeed indicator markings chart are based on the Section 5 airspeed calibration for the normal static source. Select the alternate static source and those calibrations no longer apply exactly, so ample margins should be observed for the difference.

The limiting speeds

Four limits and a window restriction. Two of them — never exceed and maximum window open — happen to share the same number, which is worth knowing so you do not mistake one for the other.

Read each with its condition

• V_NE, 163 KIAS — not to be exceeded in any operation.

• V_NO, 129 KIAS — not to be exceeded except in smooth air, and then only with caution.

• Maximum window open speed, 163 KIAS — not to be exceeded with the windows open.

V_FE is stated twice because the limit changes with how much flap is out. The first ten degrees are permitted up to 110 KIAS; beyond ten degrees and out to thirty, the ceiling drops to 85 KIAS. At that setting the calibrated and indicated figures happen to be identical.

Manoeuvring speed changes with weight

V_A is the only entry in the chart with three values, and the reason is that a lighter aeroplane reaches its limit load factor at a lower speed. Interpolating downwards is the safe direction; assuming the 2550 lb figure at a light training weight is not.

NOTE — Full or abrupt control movements must not be made above manoeuvring speed.

The manoeuvring speeds tabulated in the chart apply to normal category operations. In the utility category the figure at 2200 pounds is 98 KIAS.

Certification

The Model 172S is certificated under FAA Type Certificate No. 3A12. That number is the authority behind every limit in this chapter.

Check yourself

• State V_NE and V_NO in indicated knots, and the condition attached to each.

• What are the two V_FE limits, and what flap settings do they apply to?

• Why does manoeuvring speed have three values, and which way does it move as weight falls?

• What must you allow for if the alternate static source is selected?

• Above what speed are full or abrupt control movements prohibited at 2550 pounds?

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