A320 APU Bleed after landing
 

Hi guys,
Apology for this silly questions.
During docking the aircraft, with a condition APU is available.
Some of my instructor, instructed me to turn on the APU BLEED after 3 minutes IDLE power have been reached after landing while and the aircraft is just couple meters from parking bay.
While others instructors, instructed me to turn on the APU BLEED once the aircraft is stoping with the condition parking break is SET.

As far as my understanding, the APU BLEED is used as an Air Condition, after the engine shut down.
My question is how is the APU BLEED connection with ENGINE BLEED related to safety before engine shutdown?

Thanks in advance guys

For safety, they may want APU bleed available to spin an engine in the event of a tail pipe failure.

For pax comfort you would want the APU up and running bleed on / available before shutting engines down to keep the air con running.

When its started and when bleed is selected is an airline decision I would think. Pax comfort, safety, wear and tear, fuel savings etc. I'll leave that to A320 pilots.

I haven’t looked this up to check the detail, but I am fairly sure that if there is an interruption in the bleed air supply to the packs, it constitutes an extra pack cycle, which causes wear in the pack components.

(not sure how or why this wear occurs, but must be something to do with spinning up the air cycle machine).

This is why Airbus tell you to select APU bleed on just before turning off the engine masters.

Happy to be corrected.

Check airman
Main consideration for APU bleed is it sucks in engine fumes. APU starting takes 40 seconds and if you start it after engine shutdown till 5% N1 it has to be atleast close to one minute delay and it will recycle packs. So as Uplinked says it could bring in another aspect. So it's an issue which needs to be airline policy rather an individual technique. In Airbus best thing is to refer it to Airbus which will consider these aspects in their answer. Personally I would not cut it so fine. APU has nothing to do with 3mts.

I just do exactly as per FCOM. Parking brake ON, APU Bleed ON, then engines shut down. Never heard any complains about smell of exhaust gasses in the cabin.

PRO-NOR-SOP-22
 

FCOM / SOPs / Parking -> APU Bleed.....ON, just before engine shutdown, to minimise odours of engine exhaust fumes air conditioning.
Your company procedures may vary but I doubt it's after ENG Shut down.
Hope this helps.

FCOM rules. Reasons stated by vilas already.

I think C/A means he waits with bleed selection, not the APU start itself. Still a pack cycle.

Now, speaking of when to start the APU... :}

The APU start is related, to have a bleed source available for the tailpipe drill. Acoording to OEM.

@ Check Airman: My sense of smell is pretty weak. Maybe also flying in China with the pollution, I can't distinguished.:} xD

Thanks guys for the info, after more depth reading I just figure it related safety in regard to tail pipe.
However if you think I am wrong, I am so happy to be corrected.

Correct, although we have changed our procedures over a year ago after consultation with Airbus as statistically speaking tail pipe fires on shutdown are so unlikely that we can afford to keep the APU bleed off at engine shutdown and put it on if/when needed.