BK117 Machine swap.
I flew the first leg to the main base. The then Co-Pilot went in the waiting helicopter and started it up - I joined rotors running.
Because of my relatively big feet I don't fiddle them through the bend in the cyclic but move them over the seat so I noticed only short after T/O.
I told him, that he has to return - there's something wrong. It took some pointing out until he saw it too....
The cyclic on the Co-Pilot-Side was installed 180 degrees turned ....
Guess he skipped the full and free movement part of the checklist....