At what altitude is DME or suitable RNAV required if VOR navigational equipment is in use?

The correct answer is based on regulations that dictate the use of navigational aids at different altitudes to ensure safe and effective navigation. When VOR (VHF Omnidirectional Range) navigational equipment is in use, the requirement for Distance Measuring Equipment (DME) or suitable Area Navigation (RNAV) systems kicks in at or above 24,000 feet Mean Sea Level (MSL). This mandate is established by the FAA to enhance navigational accuracy and provide redundancy in navigation systems when operating at higher altitudes.

The requirement at this altitude ensures that pilots have access to precise positional data, which is crucial for maintaining situational awareness and for adherence to air traffic control directives. At these higher elevations, the limitations of VOR navigation, such as signal line-of-sight and potential interference, highlight the necessity for supplementary navigational aids like DME or RNAV.

This understanding illustrates the commitment to flight safety and operational efficiency in the National Airspace System, particularly as aircraft operate in more complex airspace environments.