Poor Engineering Department of PIA did not pay attention to the corrosion in the toilet which was just above the unpressurized bulkhead.The corrosion caused a gap between the presurized and the unpressurized area,causing the unpressurized area to suck in the lose items in the toilet which flew and blocked the control cables and put the aircraft in a pitch-up mode.The aircraft started to climb and both the pilots tried to control it as the angle of attack was leading towards a stall and managed to control it through the assistance of another pilot travelling on the Jumpseat.
The aircraft had gotten depressurized and the oxygen masks were deployed (half of them unserviceable).By the way the Director Engineering has been fired (Good Riddance) .