Definition
The ability of an instrument approach procedure, navigation system, or aircraft to provide precise vertical and lateral guidance to a runway, allowing descent to a published decision altitude with the accuracy and integrity required for a precision approach. In the WAAS context, this refers to LPV and other approach types that meet ICAO precision approach performance standards, providing course and glidepath guidance equivalent to an ILS.
Plain English
The system can guide the aircraft down to the runway using both side-to-side and up-and-down information accurate enough to fly a tight, low-minimums approach.
Context Anchor
Seen in WAAS and RNAV GPS approach discussions, especially when explaining why a GPS approach can provide vertical guidance similar to an ILS.
Derivation
From Latin praecisio, meaning 'a cutting off' or 'exactness.' A precision approach is one where guidance is exact enough in both directions (lateral and vertical) to bring the aircraft very close to the runway before requiring visual contact.
Why Pilots Care
It determines whether an RNAV approach can be flown to lower minimums with vertical guidance rather than higher non-precision minimums.
Grounding Statement
Precision approach capability means the system is not just showing where the runway is left or right; it is also giving an approved path down toward it.
Intuition Check
Do not read this as simply “the pilot flies very precisely.” Here it means the equipment and procedure are approved to provide both accurate sideways guidance and vertical descent guidance.
Example Sentence 1
Because the aircraft was equipped with WAAS, it had precision approach capability and could fly the LPV down to a 250-foot decision altitude.
Example Sentence 2
Without WAAS, the receiver lacked the precision approach capability needed for vertical guidance on the RNAV procedure.