C-GAQN, a DHC-8-311 operating as North Cariboo Air flight NCB5109, was in cruise en route from Christina Lake, AB (CCL3) to Kelowna, BC (CYLW) when the left main landing gear aft door opened fully. The flight crew received a gear door light indication and a landing gear INOP caution light. The crew diverted to Vancouver, BC (CYVR), declared a PAN PAN PAN, and requested emergency services stand by. The landing gear was extended manually and the aircraft landed at CYVR without further incident.
Company maintenance inspected the aircraft, swung the gear, and performed a test flight with no faults found.
The Proximity Switch Electronics Unit (PSEU, p/n 8-586-01) was replaced as a precautionary measure.