Aircraft Approach Category and Minimums
 

If an aircraft which normally falls in the Approach Category C (Speed 12-140) has an approach speed of more than 141 on a particular approach due to some reason like a failure which necessitates a higher approach speed or due to the aircraft being heavy, will the DA also change? This situation very often happens in the A321 when the aircraft is heavy>

It was an issue in the 737-800, which was purely category C in our operations although approach speeds were over 140 kts in normal operation already. We never had to adjust minima, it was treated still as category C in non-normal situations, especially stuck slats/flaps which leads to much higher speeds, OEI was flown at flaps 30 since we had the fail operational autopilot which is approved for that.

The A321, however, is always category D in the company i fly for.

It probably depends if you fly PANS-OPS or TERPS.

This issue is going back and forth at the present time in the U.S. with industry and the FAA. We have old TERPs circling criteria and new TERPs circling criteria. The transition won't be complete for years. Then we have old turning missed approach criteria for VOR/NDB/ILS and we have new turning missed approach criteria for RNAV IAPs. RNAV criteria permits a speed limit in the missed approach turn. If that speed is significantly exceeded the results could be unpleasant, particularly with an OEI slow climber.

The category that applies will be based on the higher speed. If you fly a cat c aircraft at a cat d Vref you must use cat d minima. However you cannot do it the other way round and reduce the category the aircraft was certified in. Of course, in an emergency you will do whatever has to be done.

Which speed is used for these measurements? GS TAS or CAS. I hav never heard of changing the minimums due to aircraft speed. Even in the sim with overweight and flap/slat faults we always stuck in aircraft certified cat in.

Why even bother with that Cat stuff why don't the charts just replace them with speed ranges and their associated minimums?

...which speed
Vref,
Historically, all-weather approaches would involve some manoeuvre, lateral and/or vertical. Nowadays this is more relevant to a NPA or some Cat 1 ILS approaches, but with RNAV FMS etc this is less of a problem.

The higher category margins provide additional time to manoeuvre at higher speeds and to a lesser degree consider the aircraft inertia and ability to manoeuvre; again these are now less of a problem.
However these category additions also apply to holding patterns, joining, and intermediate approach procedures; and perhaps of greater relevance today, for missed approaches.
Thus it could be hazardous to assume that the use of a single category will cover all circumstances.