Thank you for the trip report!
Could you please quickly elaborate how you made it to this tunnel at FRA. This tunnel connects Terminal 1A/Z with Terminal 1B. The tunnel is Schengen and clean (after security).
Until now I was not aware of a direct pathway between Terminal 1B (either Non-Schengen Departure clean or Non-Schengen Arrival un-clean) to this tunnel. Because they is no direct pathway between either Non-Schengen Departure clean or Non-Schengen Arrival un-clean to Schengen clean.