In the context of an ILS approach, what is required if a TACAN fails and RNAV substitution is not authorized?

In the context of an ILS (Instrument Landing System) approach, if the TACAN (Tactical Air Navigation) component fails and RNAV (Area Navigation) substitution is not authorized, the requirement for alternate missed approach instructions becomes essential. This is because TACAN typically aids in navigation during the approach, and without it, pilots may lack crucial guidance necessary for executing a safe and effective missed approach procedure.

Having alternate missed approach instructions allows the pilot to follow a predetermined route to safely exit the approach and enter a holding pattern or proceed to another approach, ensuring safety in the event that the ILS cannot be completed due to the loss of TACAN navigation. It provides a structured response to a failure, enhancing situational awareness and adherence to established safety protocols. By having an alternative plan readily available, the pilot can maintain control and prevent complications that might arise from the loss of navigational aids during critical phases of flight.