ACS tolerances

The Private Pilot Airplane ACS (FAA-S-ACS-6C, effective May 31, 2024) anchors forward-slip tolerances around runway centerline alignment (ground track held throughout the slip), airspeed control, and a clean recovery to a normal landing.

The tolerances at a glance

Parameter	Target	Tolerance	Reference
Airspeed during slip	Manufacturer-recommended	±5 KIAS	V.G.S2
Ground track	Runway centerline	Aligned	V.G.S1
Recovery	Transition to normal landing	Smooth, well above flare	V.G.S3

Plus structural requirements:

• Establish a forward slip with the airplane aligned with the runway centerline — V.G.S1
• Steady descent path with proper airspeed control — V.G.S2
• Recover from the slip and transition to a normal landing — V.G.S3

Airspeed ±5 KIAS

The published airspeed tolerance is anchored to the manufacturer's recommended slip airspeed (typically the same as V_REF). Reliable airspeed indication during the slip depends on the airplane — a yawed airplane's pitot may read inaccurately because the relative wind isn't aligned with the tube.

Practical implication: in the slip, trust the pitch attitude more than the airspeed indicator. Establish the slip with a known-good pitch attitude; if the indicator reads slow but the attitude is correct, the indicator is probably wrong.

Runway centerline alignment

V.G.S1 requires the ground track to follow the centerline during the slip. The airplane's heading is offset (nose pointed away from the rudder side), but the track over the ground is centerline. The DPE evaluates by watching how the runway centerline tracks under the airplane during the slip.

This is the diagnostic for a proper slip: the airplane is yawed but flying straight along the centerline. Yawed and tracking off-centerline isn't a slip — it's poor rudder coordination.

Recovery to a normal landing

V.G.S3 requires a smooth transition from the slip back to a normal landing approach. No published recovery altitude is specified, but the slip must be fully recovered before the round-out. A slip continuing into the flare is a bust.

The DPE evaluates by watching the airplane re-stabilize on a normal approach picture before the round-out: wings level, nose aligned with centerline, ball centered.

What the maneuver does not require

• No specific bank angle — the slip's bank is whatever produces the desired descent rate. Light slips at 10° bank, aggressive slips at 25–30°.
• No specific descent rate — the standard is steady, not fast. Both gentle and aggressive slips are acceptable so long as they're stable.
• No specific entry altitude — slips can begin anywhere on final where high-on-glidepath is recognized.