Your approach category deals with more than just the circling approach. It determines your maximum speeds, maneuvering airspace, and obstacle clearance on approach as well as missed approach. It is always based on your maximum certificated landing weight, though that can be changed. The speed that is used might be different between ICAO and U.S. FAA, depending on aircraft.
The United States FAA has long subscribed to a dangerously narrow circling approach area that has already killed and will kill again if you don't understand the problem. (See Normal Procedures & Techniques / Circling Approach Area for more about this.) The case of Air China 129 is one where a Boeing 767 was trying to circle to what were TERPS standards back then and ended up losing the airplane and 129 lives. TERPS standards have since changed but most U.S. circling procedures have not.
So what's the bottom line here? You need to understand exactly what your aircraft's circling capability is, what the correct approach category is, when you can change it, and what all that gives you for any particular airport.
What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue.
[14 CFR 97.3] Aircraft approach category means a grouping of aircraft based on a speed of VREF, if specified, or if VREF is not specified, 1.3VSO at the maximum certificated weight. VSO, and the maximum certificated landing weight are those values as established for the aircraft by the certification authority of the country of registry.
These categories are as follows:
There are some who would argue that maximum certificated weight only applies to 1.3VSO based on the placement of a comma in the regulation. Specifically, the CL-604 has a VREF based on 1.23VSO and some in that community argue that 14 CFR 97.3 means their approach category is not based on maximum landing weight. Nonsense! Even if this were so — it's not — you could not use that when flying outside the United States...
[ICAO Doc 8168 PANS-OPS Vol 1, §4, ¶1.3]
1.3.1 Aircraft performance has a direct effect on the airspace and visibility required for the various manoeuvres associated with the conduct of instrument approach procedures. The most significant performance factor is aircraft speed.
1.3.2 Accordingly, categories of typical aircraft have been established. These categories provide a standardized basis for relating aircraft manoeuvrability to specific instrument approach procedures. For precision approach procedures, the dimensions of the aircraft are also a factor for the calculation of the obstacle clearance height (OCH). For Category DL aircraft, an additional obstacle clearance altitude/height (OCA/H) is provided, when necessary, to take into account the specific dimensions of these aircraft (see Part II, Section 1, Chapter 1, 1.3).
1.3.3 The criterion taken into consideration for the classification of aeroplanes by categories is the indicated airspeed at threshold (Vat), which is equal to the stall speed Vso multiplied by 1.3, or stall speed Vs1g multiplied by 1.23 in the landing configuration at the maximum certificated landing mass. If both Vso and Vs1g are available, the higher resulting Vat shall be applied.
1.3.4 The landing configuration that is to be taken into consideration shall be defined by the operator or by the aeroplane manufacturer.
1.3.5 Aircraft categories will be referred to throughout this document by their letter designations as follows:
These speeds are the same as used in the United States but the criteria is slightly different. If you have a VSO and a VS1G for your aircraft, you must use the higher of VSO times 1.3 or VS1G times 1.23.
Regardless of the speed used, it must be based on the aircraft's maximum certificated landing mass. More on this below under The Variable Approach Category Mess.
While the speeds used for determining approach categories are based on maximum certificated landing weight, the maximum speed actually used for approach can be different.
[Aeronautical Information Manual §5-4-7] A pilot must use the minima corresponding to the category determined during certification or higher. Helicopters may use Category A minima. If it is necessary to operate at a speed in excess of the upper limit of the speed range for an aircraft's category, the minimums for the higher category must be used. For example, an airplane which fits into Category B, but is circling to land at a speed of 145 knots, must use the approach Category D minimums. As an additional example, a Category A airplane (or helicopter) which is operating at 130 knots on a straight-in approach must use the approach Category C minimums. See the following category limits:
In the U.S., the maximum speed for determining an approach category is also the maximum speed for maneuvering. If the pressure altitude, winds, temperature, or any other factor requires you to increase your maneuvering speed, your turn radius goes up and the obstacle clearance is no longer guaranteed. You must increase your approach category. Back to the case of the CL-604: under ideal conditions you could get that airplane's VREF at maximum weight down to 140.5 knots but the airplane circles at 150 knots, throwing out all their arguments saying they are Category C.
[ICAO Doc 8168 PANS-OPS Vol 1 §4, Table I-4-1-2]
While the speed ranges used to determine an aircraft's approach category are identical to 14 CFR 97.3, ICAO Doc 8168 PANS-OPS Vol 1 §4, ¶1.3.5, the maximum permitted speed for visual maneuvering is significantly higher. Additionally, speed ranges are specified for other segments of the approach. While it is true the speeds permitted are higher, the circling approach area is larger too. (See Normal Procedures & Techniques / Circling Approach Area for more about this.)
The maximum glide path angle depends on vertical guidance. If you have vertical guidance and are flying a PA or BARON NAV approach, the maximums are listed as follows:
[TERPS, Volume 3, ¶2.5, Table 2-2A] Precision Approach (PA) and Barometric Vertical Navigation (BARO NAV) Approach Procedure Construction, Maximum Authorized GPA's
|A (80 knots or less)||6.4|
|A (81 - 90 knots)||5.7|
|D & E||3.1|
If you do not have vertical guidance the maximums become a bit murky:
[TERPS, Volume 3, ¶252.] Vertical descent angle (VDA) is normally used in this segment for non-precision procedures. Determine the VDA for all NPA procedures except those published in conjunction with vertically-guided minima or no-FAF procedures w/out stepdown fix(es). See applicable chapters/directives for guidance on no-FAF or procedures published with PA and APV minima. Optimum VDA is 3.00 degrees. Where operationally feasible, design straight-in NPA procedures (all CATs) to achieve a VDA equal to the commissioned angle of an installed visual glideslope indicator (VGSI) if within the standard VDA range. When a VGSI is not installed or not within the standard range, or final is circling aligned, design procedures at the optimum VDA when possible or within the following range:
Note 1: Minimums VDA N/A to circling only procedures.
Note 2: CAT D/E VDA above 3.50 degrees must be annotated "Not for Civil Use."
Figure: T-38 Approach Category, from Technical Order 1T-38A-1, pg. 9-2.
We used to say you can move your category up, but never down. Alas, that isn't really true. In the case of the T-38, we thought of ourselves as Category E unless we were light enough to be Category D. Not too long ago most Gulfstreams had Aircraft Service Changes that allowed the pilots to simply turn a placard in the cockpit to magically change from Category D to Category C. The FAA got wind of this and those days are over. Now, for us civilians, there is just one recognized method of lowering approach categories.
The FAA allows operators to legally reduce an aircraft's maximum certificated landing weight which allows them to reduce to a lower approach category. This is not something a pilot can do, it requires maintenance logbook action. In the case of the G450, for example, Gulfstream Aircraft Service Change 007 must be installed. Once that is done, the aircraft's maximum landing weight drops from 66,000 lbs to 58,500 lbs and the aircraft becomes Category C. To undo this action, the ASC must be legally removed from the aircraft by logbook action. Some would say even the paperwork instituting ASC 007 must be physically removed from the airplane. (More on this at: G450 Approach Category.)
Portions of this page can be found in the book Flight Lessons 2: Advanced Flight, Chapter 17.
Portions of this page can be found in the book International Flight Operations, Part VIII, Chapter 8.
14 CFR 97, Title 14: Aeronautics and Space, Standard Instrument Procedures, Federal Aviation Administration, Department of Transportation
Gulfstream G450 Aircraft Service Change 007C, Maximum Landing Gross Weight, 58,500 pounds, Category C, Provisions, October 26, 2011
ICAO Doc 8168 - Aircraft Operations - Vol I - Flight Procedures, Procedures for Air Navigation Services, International Civil Aviation Organization, 2006
Technical Order 1T-38A-1, T-38A/B Flight Manual, USAF Series, 1 July 1978
United States Standard for Terminal Instrument Procedures (TERPS), Federal Aviation Administration 8260.3B CHG 25, 03/09/2012