AF Form 3642: Circling Computations Guide (Download PDF)

AF Form 3642: Circling Computations Guide (Download PDF) – AF Form 3642, titled Circling Computations, is a specialized U.S. Air Force form used to document and calculate parameters for circling approaches during instrument flight procedures. It supports safe execution of circling maneuvers when a straight-in landing is not possible or practical from the final approach course.

This article explains the purpose of the form, how it fits into USAF instrument procedures, key computations involved, and provides guidance for U.S.-based Air Force pilots, navigators, and flight planners. The official fillable PDF is available for download directly from Air Force e-Publishing: AF Form 3642 PDF.

What Is a Circling Approach in USAF Operations?

A circling approach is an instrument approach procedure (IAP) that allows the pilot to maneuver visually around the airport to align with a runway not aligned with the final approach course. It is common when the instrument guidance (ILS, LOC, VOR, TACAN, etc.) leads to one runway but wind, traffic, or runway configuration requires landing on another.

USAF guidance emphasizes strict adherence to protected airspace, minimum descent altitude (MDA), and visibility requirements. Circling is typically more demanding than straight-in approaches because it requires maintaining visual contact with the runway environment while staying within the circling protected area (determined by aircraft category and TERPS criteria).

Key USAF References:

  • AFMAN 11-202 Volume 3 (General Flight Rules)
  • AFMAN 11-217 (Instrument Flight Procedures)
  • TERPS (Terminal Instrument Procedures) criteria used for approach design

Circling minimums are published on IAP charts and apply to the aircraft’s approach category (A through E), based on approach speed (1.3 × stall speed in landing configuration).

Purpose of AF Form 3642

The form standardizes circling computations for USAF aircrew. It helps calculate or verify:

  • Required circling radii and protected airspace
  • Minimum descent altitudes adjusted for specific conditions
  • Maneuvering distances and timing
  • Obstacle clearance considerations specific to the aircraft and airfield

It is often paired with related forms such as AF IMT Form 3640 (Nonprecision Computations). Older versions are sometimes referred to as AF IMT Form 3642 (1993-era Information Management Tool format).

Aircrew use it during mission planning, instrument proficiency training, and actual operations to ensure compliance with protected circling areas and to document computations for safety and standardization.

When to Use AF Form 3642?

Use the form when:

  • Planning or briefing a circling approach from any instrument procedure (ILS, LOC, VOR, TACAN, RNAV, etc.).
  • The published procedure requires or allows a circle-to-land maneuver.
  • Computing custom adjustments for aircraft performance, airfield specifics, or higher commander-directed minimums.
  • Training or evaluating circling proficiency (common in USAF pilot training syllabi).

Note: USAF policy often restricts or prohibits circling in certain conditions, such as at night, with certain bird strike risks, or below specific weather minima. Always cross-check with the specific aircraft flight manual, MAJCOM supplements, and AFMAN 11-202V3.

Key Elements of Circling Computations

Circling protected areas are based on FAA/TERPS criteria adapted for military use. The radius of the circling area increases with aircraft category and MDA height:

Typical Aircraft Approach Categories (1.3 Vso):

  • Category A: < 91 knots
  • Category B: 91–120 knots
  • Category C: 121–140 knots
  • Category D: 141–165 knots
  • Category E: ≥ 166 knots

The protected radius is designed to provide obstacle clearance during the visual maneuvering segment. Computations on AF Form 3642 typically involve:

  • Determining the appropriate circling radius for your aircraft category and the published MDA/HAA (Height Above Airport).
  • Verifying that the aircraft can remain within the protected airspace while maneuvering at or above MDA.
  • Accounting for wind, true airspeed, bank angle, and turn radius during the circle.
  • Calculating time or distance to complete the maneuver.

USAF aircrew must remain at or above the published circling MDA until the aircraft is in a position to make a normal descent to landing. Descent below MDA is only authorized when the runway environment is in sight and the aircraft is in a position for a normal landing.

Important Safety Notes:

  • Circling approaches have higher risk due to the visual segment and potential for loss of visual reference.
  • Many USAF units apply higher-than-published minimums or restrict circling at night or in marginal weather.
  • Always review current FLIP (Flight Information Publications), NOTAMs, and airfield-specific procedures.

How to Fill Out AF Form 3642?

While the exact block-by-block layout is detailed in the official PDF, typical sections include:

  • Mission/aircraft data
  • Approach procedure identification
  • Aircraft category and speeds
  • Published circling MDA and visibility
  • Computed radii or maneuvering distances
  • Wind corrections and turn calculations
  • Remarks or special considerations (e.g., obstacles, lighting)

Best Practices:

  1. Download the latest version from the official Air Force e-Publishing site.
  2. Complete the form during pre-flight planning as part of your instrument approach briefing.
  3. Verify all computations against the aircraft performance manual and current TERPS-based charts.
  4. Retain the completed form as part of training or mission records per applicable AFI requirements.

For hands-on training, USAF students and instructors often review circling procedures using simulators before flying the maneuver in the aircraft.

Download AF Form 3642

Official Source:
Download AF Form 3642 – Circling Computations (PDF)

Always use the version hosted on e-publishing.af.mil for the most current form. Third-party sites may host outdated or unofficial copies.

Additional USAF Circling Approach Resources

  • AFMAN 11-202V3: General flight rules covering approach procedures and circling restrictions.
  • AFMAN 11-217 Series: Detailed instrument flight procedures.
  • Local MAJCOM or wing supplements for aircraft-specific guidance (e.g., F-16, C-130, T-6, etc.).
  • FAA Instrument Procedures Handbook (cross-reference for foundational knowledge, though USAF follows military TERPS).

Conclusion

Mastering AF Form 3642 Circling Computations is essential for safe and effective instrument operations in the U.S. Air Force. Proper use ensures aircrew maintain obstacle clearance, comply with protected airspace, and execute circling maneuvers professionally.

Whether you’re a student pilot at Columbus AFB, a seasoned instructor, or operational aircrew, treating circling approaches with disciplined planning and strict adherence to MDA and visibility minimums reduces risk significantly.

Pro Tip: Incorporate AF Form 3642 into your standard instrument proficiency checklist and review it during every circling approach briefing.

For the latest forms, regulations, and FLIP updates, visit the official Air Force e-Publishing portal and consult your unit standards officer or instrument examiner.

This guide is for informational purposes and does not replace official Air Force instructions or flight manuals. Always refer to current publications and chain-of-command guidance.

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