Instrument procedures
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Frequently asked questions
What is a position fix?
A position fix is a determination of the aircraft's geographic location at a given moment from external references. Cross-bearing fixes use two or more VOR radials; range fixes use DME; combined fixes use one bearing and one range. Modern GNSS provides a continuous fix; traditional fixes form part of skills tests.
What is DME slant range?
DME measures the line-of-sight distance from the aircraft to the ground station, not the horizontal distance over the ground. At low altitude or large range, slant range and ground range are nearly equal; directly overhead at altitude, slant range equals altitude regardless of horizontal position.
What is a procedure turn?
A procedure turn is a charted course-reversal manoeuvre used during an instrument approach to align the aircraft with the final approach course. The two common types are the 45/180 (45° offset for a timed leg, then a 180° turn back) and the 80/260 (80° offset, then a 260° turn).
What is a DME arc?
A DME arc is a curved flight path flown at a constant DME distance from a ground station, used in some instrument approaches as a transition from the en-route structure to the final approach. The pilot intercepts the arc, then makes small heading changes to keep the DME constant as the bearing to the station rotates.