What can cause VOR navigation course deviation of up to 6 degrees?

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Multiple Choice

What can cause VOR navigation course deviation of up to 6 degrees?

VOR CDI readings can be affected by the aircraft’s own electrical and mechanical environment, not just by the external radio signal. When propeller RPM changes, the electrical load and engine-driven electrical systems can introduce noise or slight instability into the VOR receiver or its signal processing. That instability can momentarily cause the course indication to wander, producing a deviation on the CDI of up to about six degrees. This kind of error is more likely on older or less well-shielded installations, or during RPM transitions when electrical conditions shift rapidly. The other factors listed don’t directly cause a VOR course error in the same way. Engine vibrations mainly affect mechanical instruments; turbulence affects the flight path rather than the VOR signal itself; and weather radar interference relates to the radar system, not the VOR CDI. So the RPM-related electrical/EMI effect is the most plausible source of a small, up-to-six-degree VOR course deviation.

VOR CDI readings can be affected by the aircraft’s own electrical and mechanical environment, not just by the external radio signal. When propeller RPM changes, the electrical load and engine-driven electrical systems can introduce noise or slight instability into the VOR receiver or its signal processing. That instability can momentarily cause the course indication to wander, producing a deviation on the CDI of up to about six degrees. This kind of error is more likely on older or less well-shielded installations, or during RPM transitions when electrical conditions shift rapidly.

The other factors listed don’t directly cause a VOR course error in the same way. Engine vibrations mainly affect mechanical instruments; turbulence affects the flight path rather than the VOR signal itself; and weather radar interference relates to the radar system, not the VOR CDI. So the RPM-related electrical/EMI effect is the most plausible source of a small, up-to-six-degree VOR course deviation.

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