Final answer:
Before using the GPS landing mode, the system must be keyed and set to Approach Mode. This mode is critical for the system to properly execute final descent and landing procedures using satellite navigation.
Step-by-step explanation:
Before using the GPS landing mode, the system must be keyed and in Approach Mode. The GPS landing system, typically employed in aircraft, uses satellite navigation to provide guidance for precision landing. For the system to transition into GPS landing mode, it is necessary to ensure it is in Approach Mode, which is a prerequisite state that prepares the system for the final descent parameters and calculations required for an accurate approach and landing.