Instrument Approach Procedures
Anatomy of an approach
An instrument approach chart contains the initial, intermediate, final, and missed approach segments, each with its own obstacle clearance and design criteria. Candidates must understand the decision altitude or minimum descent altitude, the difference between a precision and a non-precision approach, and the meaning of the approach ban and required visual reference. Know how to read the minimum sector altitudes, the missed approach point, and the timing or DME fixes that define it.
Traps
A common trap is confusing DA (a decision altitude referenced to mean sea level) with DH (a decision height referenced to the threshold). Another is assuming that reaching the MDA permits descent below it without visual reference; it does not. Questions often test whether a circling approach is authorized at the stated minima and what visibility is required. Watch for the difference between the published visibility and the flight visibility required to continue.
Worked example
An approach has an MDA of 600 ft and a published visibility of 1 NM. You reach the MDA at the missed approach point with the runway environment in sight and flight visibility of 1 NM: you may land. If the runway environment is not in sight, you must execute the missed approach at the MAP, not continue.
Rule of thumb
DA/DH applies to precision approaches; MDA applies to non-precision. Never descend below MDA without the required visual reference.