What indicates a normal system condition for the ILS?

A normal system condition for the Instrument Landing System (ILS) is indicated by the absence of red lights or errors along with the presence of power. In aviation, red lights typically signify a fault or issue within the system, which could compromise safety or functionality. Therefore, a system that does not show any red lights or errors can be interpreted as being operational and ready for use. Additionally, confirming that power is present ensures that the system has the capability to function properly.

The other choices suggest conditions that do not indicate a normal operation of the ILS. For instance, multiple yellow lights might indicate caution or an ongoing issue that requires attention, while flashing green lights could denote a temporary status rather than a stable operating condition. The presence of alerts due to maintenance clearly indicates that the system is not in a standard operational state, as maintenance alerts suggest that the system may be under repair or may have underlying issues that need to be addressed.