Porter Airlines – Bombardier DHC-8-400 – Pressurization Issue

C-GLQN, a Bombardier DHC-8-400 aircraft operated by Porter Airlines, was conducting flight POE943 from Toronto/Billy Bishop Toronto City, ON (CYTZ). During the climb after the departure from CYTZ, the flight crew received a door open indication and was unable to pressurize aircraft.
The flight crew declared a PAN PAN and returned to CYTZ where the aircraft landed without further incident with ARFF standing by.
A visual inspection of the aircraft determined that the cargo door handle had popped out or was inadvertently left unlocked by ground personnel during the previous stop. The operator’s maintenance inspected and lubricated the door handle and subsequent operational checks revealed no further faults.