Radio Navigator
Glossary

Cone of confusion

Direct answer

The cone of confusion is the inverted cone of airspace directly above a VOR in which the station cannot provide usable azimuth guidance, so the indications become unreliable for a short period around overhead.

Also written as: zone of ambiguity, VOR station passage.

A VOR radiates its azimuth signal outward, not upward. Approaching overhead, the geometry degrades: the deviation needle becomes increasingly sensitive, then wanders, and the warning flag may appear. The higher you are, the wider the cone is at your level and the longer the disturbance lasts.

The correct response is to do nothing dramatic. Hold the heading you had established and wait for the indications to settle on the far side. Station passage is confirmed by a definite, sustained flag change from TO to FROM, not by the first flicker.

Where this comes up

Sources

  1. FAA Aeronautical Information Manual, Section 1-1-3 (VOR). Station passage and the zone of ambiguity overhead a VOR.
  2. FAA Instrument Flying Handbook (FAA-H-8083-15B), Chapter 9 (Navigation Systems). Practical handling of VOR station passage.

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This article does not constitute flight instruction. Always defer to the guidance of your qualified flight instructor and to current charts and procedures or regulations published by your country's aviation authority.

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