As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSPECTION TYPE:N/A ATB / EMERGENCY - NOTED PERSSURE BUMP/SWOOSH AT LIFTOFF. MAIN CARGO DOOR WARNING CAME ON AT LIFT OFF. VISUAL BACK TO LAND. LIGHT STAYED ON TILL CYCLED IN CHOCKS. REMOVED AND REPLACED MAIN CARGO DOOR ARM SWITCH. PERFORMED SYS OPS, CK'D NORMAL IAW MM 52-32-23-0. OK TURN PRESSURE DOORS. OPERATION & CK OK.