C-GSWQ, a Learjet 45 aircraft operated by Sunwest Aviation, was conducting flight CNK657 from Calgary Intl, AB (CYYC) to Fort Mackay/Albian, AB (CAL4) with 2 pilots and 7 passengers on board. During the initial climb after the departure from CYYC, the flight crew received a MAIN HYD QTY LO indication, followed by a MAIN HYD PRESS indication, associated with a decreasing hydraulic pressure.
The flight crew actioned the QRH, declared an emergency, and elected to return to CYYC.
A hold was requested in order to bring the weight of the aircraft down before the landing. The landing gear was lowered without issue and, after approximately 30 minutes of holding, the flight crew entered the approach, lowered the flaps and landed uneventfully. The aircraft retained sufficient braking capability and was able to taxi back to the operator’s facility under its own power.
The operator’s maintenance found a faulty hydraulic pressure switch