When should a VOR receiver ideally be checked for a +/- 6° tolerance?

The ideal time to check a VOR receiver for a +/- 6° tolerance is above a prominent ground landmark. This is because being over a distinct point on the ground allows pilots to accurately ascertain their position and the performance of the VOR signal. When the aircraft is directly over a known landmark, the pilot can cross-reference the VOR reading with visual cues on the ground to ensure that the equipment is functioning correctly.

This method also provides a clear reference point for verifying that the VOR is accurately indicating the correct radial. The prominent landmark acts as a fixed ground reference, supporting effective navigation and ensuring that any discrepancies in the VOR reading are readily apparent in relation to known positions. This practice is crucial for maintaining navigational accuracy during flight operations.