The pressure disappears after few seconds from starter cutout (that is almost the same time when engine bleed comes on if selected), but pressure is removed also if bleed is off.The ASU is an external cart and when it is connected to the airplane 3 conditions maybe possible:Cart connected but engine is stopped, so no air to the aircraftCart connected, engine in idle with no air suppliedCart connected, and air supplied to the tube tat connects to the aircraft.The cart is commanded by the ground crew. After the first engine start is probable that the ASU is moved to idle power. It is still connected, but not supplying air.This condition is REQUIRED for the ground crew that wants to disconnect the tube as they cannot do if it is pressurized.So, basically it is a correct feature that pressure is removed after the engine start.But, if someone wants to start the second engine, there must be an option to do it.This could be an added item in the menu or can be done by cycling the connected removed status for the ASU

I don't see why should it be possible to start the No2 with ASU still connected? Just try to think of ground crew operating the ASU and the health effect of the jet blast produced by the No2 spooling up. If you need an Air Starter because your APU is INOP then it's gonna be a No1 -> crossbleed No2 start IMO. I think it's been modelled correctly/logically but as I said it's only my opinion...

I don't see why should it be possible to start the No2 with ASU still connected? Just try to think of ground crew operating the ASU and the health effect of the jet blast produced by the No2 spooling up. If you need an Air Starter because your APU is INOP then it's gonna be a No1 -> crossbleed No2 start IMO. I think it's been modelled correctly/logically but as I said it's only my opinion...

You're rigt, but if all precautions are taken and the engines are running in idle thrust a mechanic or an handling person can walk under or near the fuselage without great risks.It is also a procedure in case you have a failed starter valve wich need a mechanic to be at one side of the engine (internal for the right one) with a Key that manually open it. After the starting procedure the mechanic will do the same path of a potential ground handling person who wants to remove the tube.For sure it exposes personnell to an added risk, and it should be avoided. But, functionally speaking, the ASU cold be used for both engines.

I believe you daviersoft, I just remember the twisting feeling in my stomach when I walked around an engine after the a/c have stopped at the gate. It wasn't too comfortable but it might be just me being too precautious... Maybe that's why I'm not an engineer who disconnects ASUs. :)