Aircraft performance significantly influences the airspace and visibility required during various maneuvers in an instrument approach procedure. Among the most critical performance factors is the aircraft’s speed. To account for this, several standardized categories, each defined by a specific speed range, have been established.

The key factor for assigning an aircraft to a specific category is the indicated airspeed at the runway threshold (VAT), measured when the aircraft is in its normal landing configuration at its maximum certified landing weight. This threshold speed is defined as the greater of either 1.3 times the stall speed (VSO) or 1.23 times the stall speed in a specific landing configuration (VS1g). The landing configuration considered can be determined by the aircraft operator or specified by the manufacturer.

These categories do not change during day-to-day operation. To change an aircraft’s category, an aircraft must be re-certified with a different maximum landing mass. Pilot may not use a lower category that the one certified, but may choose to use a higher category for higher speed approaches.