Originally Posted by
sire
If one looks at the OFF SCHEDULE DESCENT QRH, it has you do nothing at all if you land at the airport of departure. Do you have to set zero in the case of Cancun or what happens when you touch down?
Nothing special will happen when you touch down, although you'll be depressurised from roughly 5,500 ft, which may be uncomfortable! In the opposite scenario, i.e. landing at a high alt airfield after offsked descent from a low alt airfield, you would of course be landing with a cabin delta (px controller expecting lading at sea level), and therefore the aircraft would depressurise after touchdown.