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Air Traffic Services Brief -- Proposed Modification of Circling TERPS CriteriaAir Traffic Services Brief -- Proposed Modification of Circling TERPS Criteria

Air Traffic Services Brief

Proposed Modification of Circling TERPS Criteria

The Issue

In an effort to increase safety while moving toward conformity with the standards set forth by the International Civil Aviation Organization (ICAO), the Federal Aviation Administration (FAA) is proposing a change to Order 8260.3, Terminal Instrument Procedures (TERPS). This technical document provides guidance that is used in the development of instrument approaches. As part of this initiative, the FAA is planning to increase the protected circling approach areas used in the design of terminal procedures.

The Importance to Our Members

Approach minimums are published for different aircraft categories and consist of a minimum altitude and required visibility. These minimums are determined, in part; by applying the appropriate obstacle clearances outlined within the TERPS criteria. Circling approach protected areas are defined by the tangential connection of arcs drawn from each runway end. The arc radii distance varies according to aircraft's approach category (see below).

Approach Category

Radius (miles)











Accordingly, a change in the protected circling area for terminal procedures will raise the approach minima at numerous airports throughout the national airspace system.


Although likely to be viewed as a "knee-jerk" reaction to the recent crash of a Gulfstream III jet while on approach to Aspen, Colorado, this proposal has been under review by the FAA-sponsored Aeronautical Charting Forum for nearly eight years. The movement to change the circling TERPS originated with the desire to conform to international standards, which provide a much larger protected area for circling approaches. However, when the FAA studied the ICAO-prescribed areas, they were found to be larger than what was required to protect aircraft during normal operations. Computer modeling did reveal deficiencies that led to the call for larger protected areas, particularly for category-C and D aircraft. With this information, the FAA proposed a compromise for category A-D aircraft that was larger than the existing TERPS area, yet smaller than the ICAO standard.

AOPA's Position

In its letter to Flight Standards, AOPA strongly urged the FAA to avoid a "cookie-cutter" approach to circling TERPS by retaining the existing protected area criteria for category-A aircraft. Although AOPA is supportive of those procedural changes that are proven to enhance safety, the FAA has failed to present any compelling evidence to date that would justify this proposal for category-A aircraft. A search of both the FAA's Incident Data System and the National Transportation Safety Boards Accident/Incident Data covering a 20-year period revealed no cases in which inadequate terrain protection was cited as a primary or causal factor. This is not to suggest that an accident is necessary to trigger a safety enhancement. However, given the number of circling approaches conducted and the conspicuous absence of any catastrophic events related to protection criteria, it is clear that the current guidelines provide pilots of category-A aircraft with an acceptable level of safety.

The following highlights our concern in this matter:

  • The computerized modeling data presented by Flight Standards fails to demonstrate a need for the proposed change.
  • Flight Standards has failed to show due diligence by not conducting the "real world" testing necessary to validate the need for change.
  • The FAA's obstruction evaluation process has proven adequate in protecting instrument approaches. An increase in the protected area without a subsequent change to the obstruction standards of Title 14 CFR Part 77 would penalize the GA community both in terms of protection and lower approach minima.
  • Resources committed to re-assessing existing approaches would be better spent developing new approaches, which would offer improved overall system safety (and access).
  • The proposed circling area is larger than a visual flight rules (VFR) traffic pattern. Operational experience has shown that a protected area of that size is simply unnecessary to contain category-A aircraft.
  • The resulting penalty in terms of approach minimums appears contrary to other initiatives put forth by the FAA to encourage the GA community to increase their usage of the instrument flight rules (IFR) system.

AOPA is willing to defer to the operational expertise of other industry representatives in evaluating the stated need for an increase in category-C and D protection criteria. For category-B aircraft, AOPA would like to see additional testing to include flight-path variations resulting from changes in density altitude. A study of this type is instrumental in validating the need for increasing the category-B protection criteria.

In short, the potential increase to approach minimums at airports throughout the country will have a profound and negative effect on the safe and efficient use of airspace by many general aviation (GA) pilots. Although there is an increased risk associated with circling approaches, especially under certain meteorological conditions, there is simply no evidence to support the FAA's contention that larger circling area criteria will mitigate any of the associated hazards. It is recognized that the greatest danger inherent to circling approaches is associated with human factors such as disorientation, poor technique, and lack of judgment. AOPA reminded the FAA that the role of TERPS is to provide a safe operating environment for pilots, not eliminate risks associated with a lack of adherence to sound operational practices.


AOPA has forwarded its comments (see below) to the FAA's Flight Standards office (AFS-400). We are also working closely with the FAA's Office of Aviation System Standards (AVN) to identify and quantify the resulting impact of this proposal to the general aviation community.

Associated Links

  1. AOPA's letter to FAA (Flight Standards)
  2. Establishing an Instrument Approach
  3. The FAA's Obstruction Evaluation Process
  4. Approach and Landing Minimums
  5. Terminal Instrument Procedures (TERPS)