ACS tolerances

The Private Pilot Airplane ACS (FAA-S-ACS-6C, effective May 31, 2024) anchors soft-field tolerances around the continuous-motion taxi, full back-elevator, liftoff as soon as practical, and the ground-effect acceleration to V_Y. The climb tolerance is the same as the normal takeoff (A); the new structural items are surface-specific.

The tolerances at a glance

Parameter	Target	Tolerance	Reference
Climb airspeed (V_Y)	After ground-effect acceleration	V_Y +10/−5 KIAS	V.C.S4
Controls position	For existing wind + to maximize lift	Visible to DPE	V.C.S1
Elevator during taxi	Full back-elevator throughout	Sustained	V.C.S2
Liftoff timing	As soon as practical	Stay in ground effect	V.C.S3

Plus structural requirements:

• Position controls for the wind and to maximize lift — V.C.S1
• Full back-elevator during taxi to keep weight off the nose — V.C.S2
• Lift off as soon as practical and remain in ground effect — V.C.S3
• Accelerate in ground effect to V_Y, then climb out at V_Y +10/−5 — V.C.S4

Climb airspeed V_Y +10 / −5 KIAS

Same as the normal takeoff (A) — asymmetric band favors flying fast over flying slow. Anchored to V_Y, not to the liftoff speed (which is typically below V_Y on a soft-field takeoff).

Full back-elevator during taxi

V.C.S2 requires full back-elevator from the moment you begin the taxi onto the runway until the nose wheel lifts. This is continuous — relaxing back pressure during the roll lets the nose wheel re-load. The DPE looks at the elevator from the right seat; visible deflection is the expected demonstration.

Liftoff as soon as practical

V.C.S3 requires liftoff as soon as the airplane can fly — even if that's at an airspeed below normal V_R. The criterion isn't a published speed; it's whether the wings are producing enough lift to support the airplane at the current pitch attitude.

After liftoff, the airplane must remain in ground effect — within roughly one wingspan of the surface — for the acceleration phase. Lifting off and immediately climbing out of ground effect is a bust.

Accelerate in ground effect, then climb at V_Y

V.C.S4 requires the airplane to accelerate in ground effect to V_Y before initiating a climb. Once V_Y is reached, the climb proceeds at V_Y +10/−5 KIAS — same standard as the normal takeoff (A).

Why the ground-effect acceleration is required. Below V_Y, the airplane is on the back side of the power curve — drag increases as speed decreases. Climbing out of ground effect at, say, 40 KIAS in an airplane with V_Y = 79 puts the climb on the back side of the curve, and the airplane won't accelerate. In ground effect, induced drag is reduced; the airplane gains speed in the same level attitude until V_Y is reached, then climbs normally.