well yeah using common sense which is why I asked this question since Airbus SOP is to switch the APU bleed to off and only switch it on again for 2nd engine start. I'm just asking making sure if its safe to do. Thanks anyway

Sorry. Perhaps I was too harsh with my reply.

There’s nothing wrong with leaving the APU bleed open. If ever we require the packs off for takeoff performance, we leave the APU bleed open to supply the packs.

Airbus do not allow X-BLEED open during Single Engine Taxi Out sure to lack of bleed leak detection in the opposite engine pylon.

My former employer's FCOM SETO procedure for the IAE-engined A320 directs pilots to open the X BLEED after ENG 1 start, so that ENG 1 will supply both packs.The X BLEED remains open until after the second engine start. The APU is left running, but the APU bleed is selected OFF to prevent the ingestion of engine exhaust gases into the air conditioning system.

On the NEO aircraft, the X BLEED is left in AUTO, the APU may be left running, but the APU bleed is selected OFF as above.

A number of airlines had self developed procedures related to the X BLEED. However, when Airbus launched RET as SOP, they made clear it must not be open.

Do you have a reference? The airline I mentioned above is not in the habit of using “self-developed” procedures.

Until the publication of a major FCOM update 18 months ago, all airlines using RETO were using their own internally developed procedures.

All operators use procedures customised in some way or other from OEM SOPs, and the manufacturer has a process to grant a “no technical objection” where changes could affect systems. In this case it appears that the OEM technical analysis when they changed their manufacturer SOP was of greater depth.

A more serious example of where customised procedures are not always properly evaluated was the 777 crash at LHR where the evacuation checklist had been split between crew members leading to spar valves remaining open as the split interrupted the intended sequence of actions.

My former employer's SETO procedure was based on that published by Airbus in the supplementary procedures section of the FCOM. It wasn't something they adopted in-house after a "no technical objection" from Airbus. If the X BLEED is no longer allowed to be selected open, then the manufacturer's guidance must have changed at some point.

I’ve always found funny that APU Bleed OFF is specifically written in the manuals in both my last and current operator FCOM yet in the FCTM it is explained that running the APU bleed with engines running(for example if you’re planning to use it to supply packs for Take Off) is more efficient than keeping the APU running while using engine bleed. And at least the second operator has modified the FCTM green operating procedure section to mention that removing the 250kt limitation bellow 10.000ft AAL is not allowed, so if they didn’t want us to use APU bleed during taxi they could have modified that section of the FCTM as well.

On a semi unrelated note, I am not sure if running the APU bleed when running single engine is more fuel efficient than keeping the APU on and using engine bleed, or if running both packs out of the APU bleed is better for cooling than a single pack out of the engine bleed.