Final answer:
Instrument landing systems (ILS) and radio altimeters are primarily responsible for monitoring aircraft ground clearance, glide-slope deviation, and sink rate, which are crucial for safe approaches and landings.
Step-by-step explanation:
Aircraft ground clearance, glide-slope deviation, and sink rate are monitored by various systems, but most notably by the Aircraft's instrument landing system (ILS) and the radio altimeter. The ILS provides pilots with the guidance necessary to approach a runway and land an airplane during both the final approach phase and throughout the landing while maintaining optimal glide-slope and centerline alignment. The radio altimeter, on the other hand, provides the actual height of the airplane above the ground, which is critical for numerous systems on the aircraft including the Ground Proximity Warning System (GPWS) that warns of potential collision with the terrain.
These systems play a crucial role in ensuring the safety of the aircraft during the most critical phases of flight - the approach and landing. They allow the flight crew to constantly assess and adjust their approach to avoid coming in too high, which could lead to a missed approach, or too low, which could result in a collision with the terrain or an obstacle. The glide-slope indicator, part of the ILS, specifically shows whether the aircraft is above, on, or below the glide path while the radio altimeter provides precise altitude above the terrain.