Approach Speed Categorisation is a system that helps to classify aircraft based on their speed during the approach phase of flight. Fixed-wing aircraft are divided into five categories. This classification is important because an aircraft’s performance directly impacts the airspace needed for various manoeuvres during an instrument approach procedure. The main factor affecting performance is the aircraft’s speed.
To standardize this, several categories with specific speed ranges have been created. These categories help relate an aircraft’s manoeuvrability and airspace needs to particular instrument approach procedures. Typically, a specific aircraft type or variant is assigned to one of these categories. The key criterion for categorization is the indicated airspeed at the runway threshold (VAT) when the aircraft is in its normal landing configuration at maximum certified landing mass. This speed is calculated as the greater of stall speed (Vso) multiplied by 1.3 or stall speed (Vs1g) multiplied by 1.23. The landing configuration is usually defined by the manufacturer or operator.
The ICAO Aircraft Approach Category table shows the specified Indicated Airspeed ranges, in knots, for each aircraft category during the approach phase. These ranges are considered by PANS-OPS approach designers when determining airspace and obstacle clearance needs for each segment of the procedure. Here are the speed ranges:
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Category A: Less than 91 knots
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Category B: 91 to 120 knots
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Category C: 121 to 140 knots
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Category D: 141 to 165 knots
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Category E: 166 to 210 knots
Each category has specific speed limits for initial and final approaches, circling, and missed approaches. For instance, a small single-engine aircraft typically falls into Category A, while a large military jet may be classified as Category E.
The FAA system, known as TERPS, uses similar speed ranges for categorizing aircraft. However, TERPS does not account for circling speeds in the same way as ICAO PANS-OPS does. According to TERPS criteria, an aircraft generally fits into only one category. If a maneuver requires a speed exceeding the upper limit of a category, the minimums for the next higher category should be applied. For example, if a Category A aircraft circles at 115 knots, it should use the Category B minimums for landing.
Here’s a quick overview of the TERPS categories:
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Category A: Speed 90 knots or less
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Category B: 91 to 120 knots
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Category C: 121 to 140 knots
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Category D: 141 to 165 knots
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Category E: 166 knots or more (mainly for certain military aircraft).
