ACS tolerances

The Private Pilot Airplane ACS (FAA-S-ACS-6C, effective May 31, 2024) anchors emergency approach and landing tolerances around best glide airspeed, field selection within glide range, planned and executed approach, and completion of the appropriate emergency checklist. The simulated maneuver doesn't actually touch down on a non-airport field; the standard is the demonstrated procedure through the approach phase.

The tolerances at a glance

Parameter	Target	Tolerance	Reference
Best glide airspeed	V_BG (per POH)	±5 KIAS	IX.B.S1
Field selection	Suitable area within glide range	Within achievable glide	IX.B.S2
Approach execution	Plan + execute to chosen field	Demonstrated	IX.B.S3
Emergency checklist	Complete and correct	Items addressed	IX.B.S4

Plus structural requirements:

• Establish best glide airspeed and configuration — IX.B.S1
• Select a suitable landing area within glide range — IX.B.S2
• Plan and execute a simulated approach to the chosen field — IX.B.S3
• Complete the appropriate emergency checklist — IX.B.S4

Best glide airspeed ±5 KIAS

V_BG is the airspeed that produces the maximum glide range — the most horizontal distance per unit of altitude lost. Like V_Y, it's published in the POH and varies by weight (decreases as weight decreases).

The ±5 KIAS tolerance is asymmetric in effect:

• Too fast → drag is higher → glide range shrinks. Some loss of distance, but recoverable.
• Too slow → on the back side of the power curve → drag also high → glide range shrinks. Worse: closer to stall.

Holding V_BG is what keeps the maximum glide range available. A pilot who departs V_BG (especially to slower) by more than 5 KIAS is reducing the field options they can reach.

Field selection — within glide range

The field must be achievable from the current altitude at V_BG. The DPE evaluates:

• Is the chosen field within glide range? The DPE knows the airplane's glide ratio; they verify the math.
• Is the chosen field the best available? Closer is better than larger; a smooth, into-wind field is better than a longer field across-wind.
• Is the selection timely? The decision should be made within the first 30 seconds of the simulated failure.

A pilot who picks a field too far away (out of glide) busts the standard. A pilot who picks the first thing in sight without applying the criteria has not demonstrated suitable selection.

Approach execution

IX.B.S3 requires planning and executing the approach. The plan includes:

• High-key / low-key pattern adapted to the available altitude.
• Configuration timing (when to add flaps, when to add gear if applicable).
• Communication timing (where in the approach to declare).

The execution includes flying the planned pattern at V_BG (transitioning to V_REF on short final), maintaining the airplane's stability, and arriving at the touchdown area with appropriate configuration.

The simulated approach typically terminates at a safe altitude (typically 500–1,000 ft AGL) rather than actually touching down on the non-airport field. The DPE evaluates the technique and decision-making through this altitude.

Emergency checklist

IX.B.S4 requires the pilot to complete the appropriate emergency checklist. This typically means the engine-failure-in-flight checklist from the POH — fuel selector, mixture, throttle, mags, etc.

The standard is complete and correct, not "from memory" — the pilot can use the POH or memory items as appropriate. Skipping items or running the wrong checklist (e.g., engine-fire checklist for an engine-out) is a bust.

What the standard does NOT require

• No actual touchdown at a non-airport field. The simulated approach terminates above ground.
• No specific glide range tolerance for "achievability." The standard is judgment-based; the DPE evaluates whether the field was a reasonable choice.
• No specific high-key altitude — the standard is the demonstrated technique, not a specific entry altitude.
• No specific communication frequency — the standard is that a declaration is made.

The standard is the demonstrated complete sequence. Fly → identify → restart → communicate → execute. Each step is evaluated. A pilot who completes the checklist (S4) and selects a field (S2) but doesn't actually fly the approach (S3) hasn't demonstrated the maneuver. Conversely, a pilot who flies a perfect glide pattern but never runs the checklist has missed S4. The maneuver requires all four standards, in approximate sequence.