Definition
A Receiver Autonomous Integrity Monitoring (RAIM) check performed by a GPS receiver for the terminal phase of flight, which begins 30 nautical miles from the destination airport. It verifies that enough satellite signals are available, with sufficient geometry, to provide the tighter accuracy and integrity required as the aircraft approaches the terminal area.
Plain English
It is the GPS's self-check that confirms it has enough good satellite signals to be trusted for navigation in the busier, more precise environment near the airport.
Context Anchor
Seen when planning or flying GPS-based instrument departures and arrivals, especially when checking whether satellite navigation can be used for that part of the flight.
Derivation
RAIM stands for Receiver Autonomous Integrity Monitoring. 'Autonomous' means the receiver checks itself without needing outside help. 'Terminal' here refers to the terminal phase of flight, the segment near an airport where tighter navigation tolerances apply.
Why Pilots Care
Confirms that GPS navigation meets integrity requirements for terminal-area operations before accepting a departure clearance.
Grounding Statement
Near the airport, there is less room for navigation error, so the receiver must be able to confirm that its position information is dependable enough for that phase of flight.
Intuition Check
Terminal does not mean the airport building here. It means the phase of flight near the departure or arrival airport. RAIM does not make GPS more accurate; it checks whether the GPS information is reliable enough to use.
Example Sentence 1
During preflight, the pilot checked Terminal RAIM availability for the expected arrival time at the destination.
Example Sentence 2
With Terminal RAIM confirmed, the aircraft could fly the initial legs of the GPS-based instrument departure without integrity alerts.