ACS tolerances

The Private Pilot Airplane ACS (FAA-S-ACS-6C, effective May 31, 2024) sets three numerical tolerances plus two structural requirements for the rectangular course. All of them are anchored to values you choose at entry — the DPE writes them down before you start.

The tolerances at a glance

Parameter	Target	Tolerance	Reference
Altitude	Entry altitude (600–1,000 ft AGL)	±100 ft	V.B.S3
Airspeed	Entry airspeed	±10 KIAS	V.B.S3
Distance from boundaries	600–1,000 ft (constant)	Stay within band	V.B.S1

Plus two non-numerical requirements:

• Rectangular ground track — track must look square-cornered from above, not parallelogram-shaped — V.B.S1
• Division of attention between aircraft control and ground track — V.B.S4

Altitude ±100 ft

Anchored to the entry altitude, which you must establish between 600 and 1,000 ft AGL before beginning the maneuver. The altimeter must read within ±100 ft of that value throughout — including during the four corner turns.

Altitude management is hardest at the steep downwind→base corner. Load factor in even a 30° bank requires noticeably more back pressure; in a 40° corner, more again. Anticipate it.

Airspeed ±10 KIAS

Anchored to the airspeed you established at entry. Two common failure modes:

• Airspeed bleed in steep corners: over-pulling on the elevator to hold altitude drags speed below the band.
• Airspeed creep on the downwind: subtle nose-low attitude during the tailwind leg lets airspeed build past the upper limit.

Distance from boundaries: 600–1,000 ft

The track must stay within the 600–1,000 ft band off every side. This is the most commonly busted item, and it's almost always failure to anticipate wind drift on the crosswind legs.

The width matters. Many students fly the course too far out and lose the visual reference. The boundary should be close enough to judge offset by eye — picture the wing root or strut as a rough sight line down to the field edge.

Rectangular ground track

The DPE evaluates the shape of the track from above, not how it felt in the cockpit. If your bank-with-groundspeed timing was wrong, the rectangle won't be a rectangle — it'll be a parallelogram, or worse, an oval. Corners should be roughly 90°.

Division of attention

V.B.S4 is the easiest item to overlook because there's no number attached. The DPE is watching for:

• Frequent scan back inside (altitude, airspeed, coordination).
• Active management of bank in turns, not eyes-fixed-on-the-corner.
• Recovery from drift before it becomes a track bust.

If you bust altitude or airspeed while watching the ground, you've failed S4 and S3. If you fly a perfect rectangle but never look at the instruments, you've still failed S4.