What altitude minimum must be maintained for an ILS approach if the glide slope is inoperative?

For an ILS (Instrument Landing System) approach, if the glide slope becomes inoperative, pilots are required to maintain a specific altitude minimum to ensure a safe descent and approach to the runway. This altitude is referenced as the Minimum Descent Altitude (MDA) for the given approach procedure.

In this scenario, the correct altitude minimum is 1,380 feet. This altitude ensures that even without the glide slope guidance, the aircraft remains at a safe altitude while proceeding toward the runway. It provides a buffer above any potential obstructions or terrain in the vicinity of the approach path, thus allowing the pilot to stabilize the approach and transition to landing safely.

The choice of maintaining 1,380 feet specifically is determined by the approach plate regulations and criteria set forth by aviation authorities, which ensure a standardized and safe altitude for operations. It's crucial to adhere to this minimum in the absence of glide slope data to prevent any risk associated with flying too low during the approach phase.