AirNavCAD v1.15: Implementing the Third Wind Spiral in Turn at Altitude Procedures

Enhancing PANS-OPS compliance, geometric accuracy and design verification.

At AirNavCAD, we continue to expand the capabilities of our flight procedure design software to address the detailed criteria defined in ICAO PANS-OPS Doc 8168.

The upcoming AirNavCAD v1.15, currently in the final validation phase, introduces support for the Third Wind Spiral in Turn at Altitude procedures — a specific design criterion that may not be implemented in some widely used flight procedure design software solutions.

Understanding the Third Wind Spiral

The Third Wind Spiral is addressed in ICAO PANS-OPS Doc 8168, Volume I, Part I, Section 4, Chapter 6, paragraph 6.4.5.2, with the associated design criteria referenced in Volume I, Part II, Section 3, paragraph 3.3.

For Turn at Altitude procedures, the construction of the protected area must account for the applicable wind spirals and their geometric relationship. The third wind spiral originates at point K′, corresponding to the inner edge of the turn initiation area at D″. It is connected to the other spirals using a line parallel to the inner edge, and the larger resulting area, incorporating two or three spirals as applicable, is used in the final construction.

The designer may choose another fix within the same turn initiation area to limit the turn initiation area and reduce the resulting protected area. However, the third wind spiral must still be considered when designing Turn at Altitude procedures, in accordance with the applicable PANS-OPS criteria.

Beyond geometry: supporting design verification

AirNavCAD v1.15 is not limited to introducing additional geometric construction capabilities. The release also includes checks covering PANS-OPS design criteria, helping procedure designers identify potential omissions and verify that relevant criteria have been considered throughout the design process.

These checks are intended to support a more systematic approach to procedure design, complementing the designer's technical judgement and validation activities.

AirNavCAD v1.15: advancing PANS-OPS automation

The implementation of specific design criteria such as the Third Wind Spiral reflects our ongoing commitment to developing software that addresses the technical detail required in instrument flight procedure design.

With v1.15, AirNavCAD continues to strengthen its capabilities in procedure construction and design verification, helping users work towards consistent application of ICAO PANS-OPS criteria.

AirNavCAD — precision in flight procedure design.

AirNavCAD v1.15 is currently in the final validation phase. The features described above are subject to completion of the release validation process.

Keywords: AirNavCAD, PANS-OPS, ICAO Doc 8168, Turn at Altitude, Third Wind Spiral, Flight Procedure Design, Instrument Flight Procedures, Aviation Safety.