Instrument Aircraft Performance, Systems, and Approach Procedures
Domain 5 combines instrument approach procedure interpretation with aircraft systems and performance, because a CFII must be able to explain why a decision altitude, a gradient, or an inoperative component changes the approach.
Reading the procedure
- Every chart has plan, profile and minimums sections: feeder and initial segments, intermediate segment, final segment beginning at the final approach fix, the missed approach point, and the missed approach. Minimum safe altitude gives 1,000 ft (2,000 ft mountainous) within 25 NM of the primary NAVAID.
- Approach categories derive from Vref at maximum landing weight, or 1.3 Vso: A at or below 90, B 91–120, C 121–140, D 141–165 kt. Minimums, visibility and circling radii change by category.
- RNAV (GPS) lines include LPV, LNAV/VNAV (baro-VNAV or WAAS), LP, and LNAV to a minimum descent altitude. LPV and LNAV/VNAV give vertical guidance to a decision altitude; LNAV does not.
- The terminal procedures 'Inoperative Components and Visual Aids' table governs the visibility increase when the approach light system, vertical guidance indicator, or another component is out. Apply the table rather than intuition.
Systems
- Static-source blockage makes the airspeed read high in a climb and low in a descent, freezes the altimeter, and leaves the vertical speed indicator near zero; the alternate static source restores indications with small errors. Pitot blockage with the drain open produces a zero airspeed indication.
- Vacuum failure removes the attitude and heading indicators first; the electrically driven turn coordinator and standby instruments carry the partial-panel approach. Glass cockpits demand familiarity with AHRS alignment and reversionary mode, not just button knowledge.
Worked example
A missed approach requires 300 ft/NM to 3,000 ft. The aircraft climbs 600 fpm at 120 kt groundspeed. Since 120 kt is 2.0 NM per minute, 600 divided by 2.0 gives exactly 300 ft/NM, with no margin. With a 30 kt tailwind the groundspeed becomes 150 kt, or 2.5 NM per minute, and the same climb yields 240 ft/NM, below the gradient. Feet per minute is not feet per nautical mile.
Traps that cost marks
- Confusing decision altitude (vertical guidance) with minimum descent altitude.
- Selecting a category from current airspeed instead of Vref at maximum landing weight.
- Comparing climb rate to a published gradient without converting groundspeed.
- Assuming a GPS database is current because the unit powers up normally.