Instrument Approach Procedures and IFR Operations
Instrument Approach Procedures and IFR Operations
The final domain tests the approach itself: category and minima, decision altitude versus minimum descent altitude, the missed approach point, circling and stabilised approach criteria.
Core rules
- Aircraft categories are set by Vat (1.3 × VSO): A <91 kt, B 91–120, C 121–140, D 141–165, E 166–210. Higher categories carry higher minima because of the larger turning radius.
- Precision approaches use a decision altitude (DA/DH); non-precision approaches use a minimum descent altitude (MDA) and you may not descend below it before the MAPt.
- ILS CAT I: DH 200 ft and RVR 550 m. CAT II: DH 100 ft, RVR 300 m. CAT III minima go lower and require fail-passive/fail-operational equipment and crew qualification.
- Circling minima are higher than straight-in and require the aircraft to stay within the protected area at the published circling speed.
- Stabilised approach: by 1,000 ft in IMC (500 ft in VMC) the aircraft should be on the correct flight path, at approach speed, with landing configuration and thrust set; otherwise go around.
Worked example
An NDB approach has the FAF to MAPt distance given as 3.5 NM. At 140 kt ground speed: 140 kt = 2.33 NM/min, so 3.5 ÷ 2.33 = 1.5 minutes - start timing at the FAF and expect the MAPt at 1:30. At the MAPt, if the runway environment is not in sight, climb immediately on the published missed approach track.
Traps
- Descending below MDA before the MAPt to "get a look".
- Using the wrong category minima after a speed increase.
- Forgetting that a go-around at DA is normal, not a failure, and must be flown on instruments to the missed approach altitude.