Anatomy of an Instrument Approach
Key facts on approach segments, DA vs. MDA, and 91.175 visibility requirements.
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Questions Covered in This Set
10 cards to master
What are the five segments of an instrument approach?
Feeder (terminal) route, initial, intermediate, final, and missed approach segments.
What is a feeder route?
A charted connector from the enroute structure to an IAF, with a course, distance, and minimum altitude; not all approaches have one (ATC often vectors instead).
Where does the initial approach segment begin, and what lives there?
At the IAF; course reversals such as procedure turns and holds-in-lieu are flown in this segment.
Purpose of the intermediate segment (IF to FAF)?
The 'get stable' segment — normally within 30° of final course, little or no descent, where you configure, slow, and finish before-landing checks.
What chart symbols mark the FAF and the PFAF/glideslope intercept?
Maltese cross for the nonprecision FAF; lightning bolt for the precision final approach point / glideslope intercept.
Obstacle clearance by segment?
1,000 ft initial, 500 ft intermediate, 250 ft in nonprecision final (a sloped surface for precision) — tolerance tightens as you get closer.
DA vs. MDA — what's the difference?
DA is used with vertical guidance (ILS, LPV, LNAV/VNAV, LDA w/GS): you go missed AT DA and momentary descent below is accepted. MDA is nonprecision: you may never descend below it without the visual requirements met.
Three conditions of 14 CFR 91.175 to descend below DA/MDA
1) Continuously in position to descend to landing at a normal rate with normal maneuvers; 2) flight visibility at or above published; 3) at least one required visual reference distinctly visible and identifiable.
With only the approach lights in sight, how low may you descend?
To 100 ft above TDZE — no lower unless the red terminating bars or red side row bars are visible.
What does 'RVR 2400' mean?
Runway visual range of 2,400 feet, measured by transmissometers near the runway (RVR is in hundreds of feet, unlike statute-mile visibility).
