SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/ifr-vor-zone-of-confusion

Why does a VOR needle swing wildly when you fly right over the station?

Because of the zone of confusion above the station.

Start playing free

  1. The station switches frequencies overhead
  2. The DME and VOR signals cancel each other out
  3. There is no adequate signal directly above the station ✔

Why: The station's antenna pattern leaves a cone with no adequate signal directly overhead. The opposing reference and variable signals produce a small, constantly changing result, so the CDI deviates from side to side.

Huh, didn't know that: VOR range grows with the altitude of the receiving aircraft, because the signals are line of sight.

The dad joke
Why did the VOR needle need a vacation? Right over the station it just lost its direction.
Like this card?
Play the game

References

Answer: There is no adequate signal directly above the station. The station's antenna pattern leaves a cone with no adequate signal directly overhead. The opposing reference and variable signals produce a small, constantly changing result, so the CDI deviates from side to side.

  1. FAA Instrument Flying Handbook (FAA-H-8083-15B) www.faa.gov/sites/faa.gov/files/pilots/FAA-H-8083-15B.pdf
    lack of adequate signal directly above the station
    Checked 2026-10-11.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

FlyingOn a VOR indicator, how many degrees off course does each dot on the scale represent?FlyingUsing VOR navigation, within how far of the VOR may you fly below the MEA down to the MOCA?FlyingAt the runway threshold, how wide is a localizer course from full-scale left to full-scale right?

That's stuff everyone should know.