Incident
The pilot in command (PIC) departed on a 14 CFR Part 135 commuter air carrier passenger flight to the destination airport. During arrival, after completing the before-landing checklist, the left main landing gear failed to extend. The nose gear and right landing gear extended but could not be retracted. The flight crew attempted emergency landing gear extension procedures without success.
Landing
The PIC requested and received clearance to return to the departure airport. Upon arrival, another attempt at emergency landing gear extension yielded negative results. The airplane was then landed on the runway, sustaining minor damage. The two crewmembers and two passengers were not injured.
Investigation
Post-landing examination by maintenance personnel revealed that the main landing gear sequencing valve had failed for undetermined reasons.