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Aircraft fall into one of five approach categories (A-E) based on the aircraft’s target final approach speed, or reference speed (Vref). If this speed is not published for the aircraft, then a speed of 1.3 times the stall speed in the landing configuration (Vso) at the maximum landing weight should be used. These speeds are established for the aircraft by the aircraft’s certifying authority. Instrument approach charts publish minimum landing criteria (altitudes and visibility) that correspond to the approach categories. If a category is not listed, then it is not authorized.
In the example below from the John F. Kennedy Airport (KJFK), ILS or LOC RWY 13L approach, the decision altitude (213′) and minimum visibility (1,800′ runway visual range), remain the same for Category A-D aircraft. However, if intending to circle to land on an alternate runway Category A & B aircraft must use a minimum descent altitude (MDA) of 680′ and visibility of 1 mile while Category C & D aircraft must abide by a MDA of 700′ and a dramatic increase in minimum visibility to 2 and 2.25 miles respectively.
A pilot is required to use the minima corresponding to the aircraft’s category or higher depending on the speed being flown during the approach. This is necessary in order to provide adequate obstacles obstruction as the higher the approach speed, the larger the turning radius in the case of a circling approach. Therefore, if a pilot chooses to use a higher airspeed than the category established for the aircraft, then the minimums for the higher category must be used. For example, if an airplane fits into Category A but is circling to land at a speed of 95 knots, the approach Category B minimums must be used. It’s important to note that a pilot may NOT choose to utilize a lower approach category even if flying at a lower airspeed.
Most single engine piston-powered aircraft will fit into Category A while most turbine-powered aircraft will fit into Category B and above.
- Category A: less than 91 knots
- Category B: 91 – 120 knots
- Category C: 121 – 140 knots
- Category D:141 – 165 knots
- Category E: More than 166 knots
A minimum of 300 feet of obstacle clearance is provided in the circling segment. Pilots should remain at or above the circling altitude until the aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent and using normal maneuvers.