TSH1202 - Incident: Aspire DH8A near Vancouver on Aug 27th 2021

An Aspire Aviation (formerly known as Regional 1 or R1 Regional) de Havilland Dash 8-100, registration C-GWRI performing flight TSH-1202 from Vancouver,BC to Masset,BC (Canada) with 23 passengers and 3 crew, was enroute at FL220 about 220nm northwest of Vancouver when multiple left hand electrical bus system malfunctions occurred without indications. The pressurization indication panel became inoperative and the cabin altitude began to climb. The crew descended the aircraft to 11,000 feet, declared PAN PAN and returned to Vancouver for a safe landing about 2:20 hours after departure.

The Canadian TSB reported maintenance found the undervoltage relay of the left hand transformer-rectifier unit faulty, the relay was replaced and the systems tested.