1)Volume is down , headset ON
2) While taking the headset OFF , ECAM pops up: Y HYD LO LEVEL
3) Simultaneously the purser wants to enter the cockpit and the buzzer sounds
4) you prioritze your tasks and fails to readjust the volume
5) You approach the FIR where you are supposed to be handed over to the next ATC.
6) For 5 minutes or more , ATC is calling you on guard.
7) Up to your imagination.
Lesson learnt : you relied on one automatism that was inhibited (cognitive function ) by a high level alert . Is your working memory so reliable ?
Try this in the sim: During rotation, distract the PF by anything like call out anything stupid "Look at EGT !! " whatever you like. PM does not call "Positive Climb" PF does not call "Gear UP" . Gear is left down for a quite a long time until the crew realizes . Some didn't until the checklist ! hopefully there is an after take off checklist but there is no "After headset OFF " checklist