What indicates that a particular VORTAC station is undergoing routine maintenance?

The identification feature of a VORTAC station is crucial for pilots to confirm they are receiving the correct navigational signal. If the identification feature is removed, it serves as an important signal to pilots that the station is undergoing maintenance or is not operating normally. This alerts pilots to the potential unreliability of the signal and encourages caution when navigating in the vicinity of that station.

Other options, while they may suggest changes in the station's operation, do not specifically indicate maintenance. For example, increased signal strength could merely be a result of atmospheric conditions or adjustments made for operational effectiveness rather than maintenance. A change in operational frequency might be due to normal operational practices rather than maintenance procedures. Extended operating hours typically imply that the station remains open for use rather than being closed for maintenance. Therefore, the removal of the identification feature is a clear and direct indication of routine maintenance activities at a VORTAC station.