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.
Plain English
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.
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 instrument approach.
Derivation
Barometric' comes from the Greek 'baros' meaning weight, referring to the weight of air measured by a barometer. 'Aiding' simply means assisting. So the term describes the barometer (altimeter) assisting the GPS.
Why Pilots Care
It enables reliable vertical guidance on GPS approaches, supporting lower decision altitudes and safer descents without full ground-based augmentation.
Analogy
It is like giving the navigation system one more trusted clue. The satellites tell it where the airplane is, and the barometric altitude helps it check whether that position makes sense.
Grounding Statement
During an RNAV approach, pressure altitude data corrects satellite position calculations so the pilot sees a stable glidepath.
Intuition Check
Barometric aiding does not mean the altimeter is flying the approach for you. It means pressure-based altitude information is helping the navigation receiver check its position solution.
Example Sentence 1
Because the receiver supports barometric aiding, RAIM remained available during the approach even though only four satellites were in view.
Example Sentence 2
With barometric aiding active, the GPS altitude matched the altimeter closely enough to continue the descent.