Which of the following is NOT a limitation of VOR systems?

VOR (VHF Omnidirectional Range) systems are crucial navigation aids for IFR flight, providing directional guidance to pilots. Among the characteristics of VOR systems, altitude restriction does not apply as a limitation.

The "cone of confusion" is a phenomenon where the VOR signal is weak and inconsistent when the aircraft is directly overhead the VOR station. This can lead to uncertainty in the indication of the aircraft's position.

Reverse sensing occurs when a pilot uses a VOR for navigation but inadvertently selects the wrong radial, creating a misleading heading indication that suggests the aircraft is moving toward the station when it is actually moving away from it.

Line of sight refers to the fact that VOR signals do not bend around obstacles such as mountains or buildings; therefore, the effective range of a VOR station can be limited by terrain or other obstructions, making it essential for pilots to be aware of their altitude relative to the station.

In summary, altitude restriction does not limit VOR systems, as they can be used at different altitudes within their operational range, provided the aircraft is within line of sight of the station and the signal is unobstructed.