Definition
An instrument approach procedure that provides the pilot with both course (lateral) and glidepath (vertical) guidance meeting precision standards, such as an ILS, PAR, or GLS approach.
Plain English
A type of approach to a runway in poor weather that gives the pilot guidance both side-to-side and up-and-down, so the airplane can be flown to a low altitude before the runway must be seen.
Context Anchor
Seen in airport information, runway marking discussions, and phrases such as “precision instrument runway.”
Derivation
From Latin praecidere, 'to cut short' — the same root as 'precise.' A precision instrument approach 'cuts close' to the runway, giving exact vertical and lateral guidance rather than approximate course-only information.
Why Pilots Care
Allows pilots to fly approaches to lower decision heights and visibility minimums than non-precision procedures permit.
Intuition Check
Precision instrument does not mean a very accurate cockpit gauge. In this context, “instrument” means instrument flight, and “precision” means approved guidance that helps line up with the runway and descend toward it.
Example Sentence 1
The ILS to Runway 27 is a precision instrument approach, so we can plan to descend to 200 feet above the ground before needing the runway in sight.
Example Sentence 2
Only runways served by precision instruments permit Category II operations in visibility as low as 1,200 feet RVR.