146/Avro RJ engine anti-ice on ground

[Mach E Avelli]

Presumably there is a balance between tapping off enough air to offload the compressors and ensuring the right amount to safely support combustion.
Selecting airframe anti ice on during ground operation is not allowed. My theory: As well as the potential for engine over temps due insufficient airflow there is the possibility that wing and tail ducting/leading edges would be cooked due lack of airflow over the external surfaces.
In any case, for airframe AI to operate you would require the separate ENG AIR switches or APU AIR to be selected on, and would get a bunch of low pressure warnings until engines were advanced to power well above idle. All air switching is required to be off during start.
Re which way the bleed bands move and when, I think 'fail safe' - in flight you don't want to be losing bleed air if something goes wrong.
The reverse logic applies to engine AI - you want it to be there in flight to cover worst case situation. Airframe AI valves fail in position selected (I think - not having the books open - but it would be typical design of the day).
As for why all start sequence switching is not done automatically to 'pilot proof' the aircraft, it is after all a very old design not far removed from the day when the Flight Engineer took care of all these technicalities.
US Air was a very early customer and had quite a substantial Bae146 operation. I did my initial training with them and was quite impressed with how practical they were. Checklists and SOPs were quite concise but seemed to cover most contingencies. The original manufacturer documentation was also quite concise, but over the years it ‘grew like Topsy’ probably to satisfy entry into EASA Land.