Which of the following is a required inspection frequency for VOR equipment?

The required inspection frequency for VOR (VHF Omnidirectional Range) equipment is indeed every 30 days. This regulation is outlined in the Federal Aviation Administration (FAA) regulations, specifically under 14 CFR Part 91.171, which mandates that VOR equipment used for IFR operations must be checked for accuracy at least once every 30 days.

This requirement ensures that the VOR navigation system remains reliable and accurate for pilots flying under instrument flight rules, thereby enhancing safety and operational efficiency. Pilots can verify the accuracy of the VOR by conducting a ground check or in-flight check using a known VOR signal, thus confirming that the equipment is functioning correctly within the required tolerances.