In order to perform an ILS using standby instruments, what condition must be met?

In order to perform an Instrument Landing System (ILS) approach using standby instruments, it is essential that Nav 1 is tuned to a valid ILS. This tuning enables the aircraft to receive the necessary guidance for both lateral and vertical approaches to the runway. When Nav 1 is set appropriately, the flight crew can utilize the standby instruments to accurately follow the ILS glideslope and localizer signals, ensuring a safe and precise landing procedure, especially in conditions where primary instruments might not be available or are compromised.

The tuning of Nav 1 allows the display systems and guidance features associated with the ILS to provide the necessary information for navigation and descent. Proper ILS functioning relies heavily on having the correct frequency tuned in, as any incorrect setting can lead to loss of guidance or misinformation, which can be critical during approach and landing phases where accuracy is paramount.