V_A — Manoeuvring speed

Definition

V_A per CS-23.335(c) is the maximum speed at which a single full deflection of one control surface will not exceed the limit load. Above V_A, full control deflection can break the airframe; below V_A, the wing stalls before reaching limit load.

Derivation

From the lift equation:

V_A = V_S1 · √n_max

with V_S1 = clean stall speed (1 g) and n_max = positive limit load (CS-23.337).

For Normal category (n = +3.8): V_A ≈ V_S1 · 1.95.

Key properties

Weight-dependent. V_A decreases at lower masses because V_S1 decreases. The AFM/POH lists V_A at MTOM and possibly at lower masses. Example, C172S POH §2 Limitations: V_A 99 KIAS @ 2,550 lb, 92 @ 2,200 lb, 82 @ 1,900 lb.

Single axis, single full deflection. V_A does NOT cover combined or repeated rapid inputs (e.g. left-right rudder reversals). American Airlines Flight 587 (2001) lost its vertical stabilizer below V_A from precisely such inputs.

Gusts. V_NO (max structural cruise) and V_B (design gust speed) are separate limits. POHs typically recommend V_A or V_B in severe turbulence.

Pitfalls

• V_A is NOT a "do anything" speed.
• Using MTOM V_A when light is unsafe (effective n increases).
• Airframe icing raises V_S1; the POH V_A assumption no longer holds.