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Instrument Rating — Airplane
Instrument Checkride Oral: Approach Minima, 91.175 & Briefing Questions
Sooner or later every instrument oral arrives at the bottom of an approach: you're at DA or MDA — what must you see to continue, and what exactly may you do? 91.175 answers all of it with three conditions and a famous list of visual references, plus the approach-light exception that buys you 100 feet. Around that core, examiners test minima-line literacy: DA versus MDA, approach categories, and what 'visibility is controlling' means.
Brief approaches the way professionals do and the oral takes care of itself: navigate the plate top to bottom (briefing strip, frequencies, final approach course, glidepath/stepdowns, DA/MDA and visibility, MSA, missed approach), and always state the missed approach point and first two actions of the miss out loud.
91.175: the three conditions and the list
To descend below DA/DH or MDA you need all three: (1) the aircraft is continuously in a position from which a descent to landing on the intended runway can be made at a normal rate using normal maneuvers; (2) the flight visibility is at least the visibility prescribed for the procedure (flight visibility — what you observe — controls, not the reported value, though large disagreements deserve suspicion and a conservative call); and (3) at least one of the listed visual references for the intended runway is distinctly visible and identifiable. The list: the approach light system, the threshold, threshold markings, threshold lights, REIL, VASI/PAPI, the touchdown zone or its markings, touchdown zone lights, the runway or runway markings, and the runway lights.
The approach-light exception: with only the approach lights in sight, you may descend to 100 ft above touchdown zone elevation — and no lower — unless the red terminating bars or red side row bars (features of ALSF-type systems) are also distinctly visible. The logic: approach lights prove you're aligned with something, but only the red elements (or the runway environment itself) prove you're close enough to the threshold to finish visually.
Minima literacy: DA vs MDA, categories, and the lines
DA (decision altitude) belongs to approaches with vertical guidance: you fly the glidepath to DA and decide there — the miss begins at DA, accepting momentary descent below it during the go-around. MDA (minimum descent altitude) belongs to non-precision approaches: it is a floor you may not descend below unless 91.175 is satisfied; you level at MDA and proceed to the missed approach point (timing, a fix, or a DME value) before missing. Derived option: a CDFA/continuous-descent technique to a 'derived DA' is an authorized-technique discussion — flag that for Part 91 pilots, the MDA remains a hard floor unless using approved procedures.
Approach categories come from 1.3 × VS0 at maximum certificated landing weight (category A under 91 knots, B 91–120, C 121–140, D 141–165) — but you use the minima for the category whose speed you actually fly: maneuver at 130 knots and you use category C minima even in a 'category A' airplane (circling especially). Visibility is controlling: the visibility value on the minima line is the legal requirement; ceiling values published alongside (military-style or airport minimums) generally aren't the Part 91 gate. Also know what makes an approach unavailable: inoperative components (consult the inop components table — e.g., ALS out raises visibility), NOTAMed unusable facilities, and 'NA at night' notes.
Practice questions with answers & rationales
Q1. You arrive at DA on an ILS and see only the approach light system. What may you do?
Answer: Continue descending — but only to 100 ft above touchdown zone elevation — using the approach lights as reference. To go below 100 above TDZE you must see the red terminating bars or red side row bars, or one of the other runway references (threshold, TDZ markings/lights, runway, etc.). If by 100 above TDZE you still see only white approach lights, go missed. This is the most-quoted sentence in 91.175 — know it verbatim.
Q2. What three conditions must all be met to leave MDA?
Answer: Position to land on the intended runway with a normal descent and normal maneuvers; flight visibility at or above the published minimum for the procedure; and a listed visual reference distinctly visible and identifiable. The 'normal maneuvers' clause has teeth at MDA: spotting the runway directly below you at the MAP doesn't authorize a diving descent — if you can't land normally, you go missed even with the runway in sight.
Q3. Tower reports visibility ½ mile; the ILS requires ¾. You're inbound and can clearly see the runway environment at DA with what you judge to be a mile of flight visibility. Legal to land?
Answer: For Part 91, flight visibility controls: if you genuinely observe at least the prescribed visibility at DA along with a listed reference and a normal landing position, you may continue. The mature add-on: a large gap between reported and observed visibility should trigger suspicion (patchy fog does exactly this), and a go-around is never wrong. Part 121/135 operators face stricter dispatch/approach bans — worth mentioning to show breadth.
Q4. What's the operational difference between DA and MDA?
Answer: DA is a decision point on a continuous descent with vertical guidance — you initiate the missed at DA and will momentarily sink below it. MDA is a floor: level off, may not descend below it without 91.175, and the missed approach point is somewhere ahead (fix/time/DME) — you can fly level at MDA to the MAP looking for the runway. Mixing the behaviors (treating an MDA like a DA without an approved derived-DA procedure, or leveling at a DA) is a downgrade either direction.
Q5. Your airplane is category A, but you're circling at 125 knots. Which minima apply?
Answer: Category C — minima follow the speed you actually fly, especially when circling, because the protected circling area is sized by category speed. Quote the source logic: categories derive from 1.3 VS0 at max landing weight, but 'if it is necessary to maneuver at speeds in excess of the category limit, use the minima for the higher category.' Circling-radius protection is the reason: faster equals wider arcs.
Q6. The approach lights are NOTAMed out of service for your ILS. Any effect?
Answer: Check the inoperative-components table (and the chart's inop notes): an inoperative ALS typically raises the required visibility for that minima line (it does not change the DA). That's exactly the kind of thing that goes in a complete approach brief — equipment status from NOTAMs cross-checked against the minima you plan to use.
Q7. Brief me the missed approach in one breath — what do examiners listen for?
Answer: The missed approach point and how it's identified, the first lateral instruction and first altitude, and who does what: e.g., 'at DA 250, if not landing: pitch up, power up, positive rate, flaps per schedule, climbing right turn to 3,000 direct ABC VOR, hold as published — I'll call missed to tower when established in the climb.' Saying the first two actions before flying the approach is the professional habit; fumbling for the plate at DA is the thing it prevents.
Common mistakes to avoid
- Forgetting the 100-ft-above-TDZE limitation on approach lights, or the red-bars exception that unlocks it.
- Treating reported visibility as controlling for Part 91 — and conversely, 'judging' visibility dishonestly. Both directions get probed.
- Descending below MDA for a runway sighted too late to land with normal maneuvers.
- Using the airplane's certificated category when circling faster — circling protection is built on actual speed.
- Skipping NOTAMs/inop tables in the brief and quoting full minima with the ALS out.
- Briefing the approach but not the miss. Examiners specifically listen for the MAP and the first two missed-approach actions.