Plain English Meaning

The GPS uses the airplane's altimeter reading as an extra piece of information. This helps the GPS keep checking that its position is accurate even when it is receiving signals from fewer satellites than normal.

Full Definition

A GPS integrity-enhancement technique that uses pressure altitude from the aircraft's barometric altimeter as an additional input to the GPS position solution, allowing the receiver to maintain or check integrity (RAIM) when fewer satellites are available than would otherwise be required.

Context Anchor

Seen in discussions of IFR GPS and RNAV approach capability, especially where the equipment checks whether it has enough reliable information to support an .