New answer due to updated FAA guidance:
The short version is that a pilot is only required to use the approach category for the aircraft's maximum certified landing weight and to stay within the protected area while circling.
However, it is recommended that if a speed higher than the maximum for that category must be used that the pilot either should use 1) the corresponding minimums for the higher category, or 2) an alternative method (i.e. company or pilot provided).
AIM 5-4-7(a) states that an aircraft must stay within the circling approach protected area during the approach.
It then says in AIM 5-4-7(b) that "one acceptable method" is to use the approach category corresponding with the speed that will be flown (certified approach category or higher).
It continues in AIM 5-4-7(c) with considerations for a pilot who chooses an "alternative method" to remain within the protected area. One example that they provide is that this may be done where higher category minimums are not published.
There is a very nice writeup on this that the NBAA released at the beginning of 2020.
From a safety perspective, the most commonly used method is that stated in 5-4-7(b), which used to be what the AIM said must be done prior to this change.
I can see where an alternative method may be useful (such as a side-step which doesn't actually require you to maneuver out of the protected area), however keep in mind that you must remain inside the protected area at all times, including during the missed approach (even if you don't expect to go missed). In some cases, the only reason for having higher minimums (or even NA) is due to the missed approach procedure obstacle clearance.
FULL TEXT OF SUMMARIZED PARTS:
AIM 5-4-7. Instrument Approach Procedures
a. Aircraft approach category means a
grouping of aircraft based on a speed of VREF at the maximum certified
landing weight, if specified, or if VREF is not specified, 1.3VSO at
the maximum certified landing weight. VREF, VSO, and the maximum
certified landing weight are those values as established for the
aircraft by the certification authority of the country of registry. A
pilot must maneuver the aircraft within the circling approach
protected area (see FIG 5-4-29) to achieve the obstacle and terrain
clearances provided by procedure design criteria.
b. In addition to pilot
techniques for maneuvering, one acceptable method to reduce the risk
of flying out of the circling approach protected area is to use either
the minima corresponding to the category determined during
certification or minima associated with a higher category. 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 should be used. This
may occur with certain aircraft types operating in heavy/gusty wind,
icing, or non-normal conditions. For example, an airplane which fits
into Category B, but is circling to land at a speed of 145 knots,
should 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 should use the approach Category C minimums.
c. A pilot who chooses an alternative method when it is necessary to
maneuver at a speed that exceeds the category speed limit (for
example, where higher category minimums are not published) should
consider the following factors that can significantly affect the
actual ground track flown:
- Bank angle. For example, at 165 knots
groundspeed, the radius of turn increases from 4,194 feet using 30
degrees of bank to 6,654 feet when using 20 degrees of bank. When
using a shallower bank angle, it may be necessary to modify the
flightpath or indicated airspeed to remain within the circling
approach protected area. Pilots should be aware that excessive bank
angle can lead to a loss of aircraft control.
- Indicated airspeed.
Procedure design criteria typically utilize the highest speed for a
particular category. If a pilot chooses to operate at a higher speed,
other factors should be modified to ensure that the aircraft remains
within the circling approach protected area.
- Wind speed and direction.
For example, it is not uncommon to maneuver the aircraft to a downwind
leg where the groundspeed will be considerably higher than the
indicated airspeed. Pilots must carefully plan the initiation of all
turns to ensure that the aircraft remains within the circling approach
- Pilot technique. Pilots frequently have many options
with regard to flightpath when conducting circling approaches. Sound
planning and judgment are vital to proper execution. The lateral and
vertical path to be flown should be carefully considered using current
weather and terrain information to ensure that the aircraft remains
within the circling approach protected area.
According to the FAA Safety Alert for Operators issued on 09/20/2012 (SAFO 12005):
- A pilot may never use the approach minimums specified for an approach category lower than their certified approach category, even if the actual approach is flown at a speed that would be in the lower approach category.
- A pilot must always use the approach minimums specified for an approach category higher than their certified approach category if the actual approach will be flown at a speed that would be in the higher approach category.
Note that this is different in other areas of the world (Canada for example uses the actual approach speed of the aircraft to determine the approach category).