4 Dogs. I think you will find it has more to do with the aircraft having auto-drop down capability of the oxygen masks rather than the pressurisation controller. If an a/c does not have auto drop down oxygen i.e. when the cabin reaches a pre-defined altitude (which in the RJ/146 is 13,250' to 14,500', the oxy masks should drop down automatically) then it is restricted to 30,000'. The older pressurisation controllers are quite capable of selecting a cabin altitude of 8000', or higher if required for zero differential at 10,000'.
The time and fuel it takes to get a heavy 146 up to that altitude sometimes negates the benefit of being up there. The loss of TAS with those poor old 502 engines above 26,000' to 27,000' can also be relevant. Unless we are doing longer sectors i.e. in excess of 1 hour 30 mins, it is hardly worth the time or effort to go to those levels, particularly when it is warmer.
I recently had the opportunity to fly a 300 nm sector out and back with little or no wind effect. We cruised at 26,000' going over and due to ATC restrictions, at 19,000' going back. We burned 20 kg's more fuel at 19,000' and got there 3 minutes earlier. So much for the benefit of climbing a 146 to altitude hey? Obviously over longer sectors there are tangible benefits at altitude.
Other considerations are temperature, headwind and icing. Godbless the poor old 146!
We could discuss this topic for quite an extended peroid of time without resolution so I will leave it at that.
[This message has been edited by shakespeare (edited 25 February 2001).]