SF 340B
Flight Crew Air Transport Pilot (ATP)
Confusion; Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Event / Encounter Object
Aircraft Aircraft Damaged
Aircraft
The First Officer; the Flight Attendant; and I boarded the aircraft to reposition it away from the customs area. I started the number two engine. I did my after start flow and waited until the gyros were spooled up. All systems checked normal and the hydraulic pressure was in the normal range. I taxied away from the parking space over to spot; which is opposite the air carrier gates. During the taxi I made two stops and three 90 degree turns. As I approached the parking spot I realized that the brakes and steering were not responding to control inputs. I pulled the fire handle to shut off the fuel to the engine. We were headed slightly downhill so the aircraft was not slowing down. We continued rolling at about 5 miles per hour. The aircraft had entered a slight left turn. The First Officer then pulled both of the condition levers back to fuel cutoff. The aircraft began turning slightly sharper to the left. After about a 180 degree turn the aircraft struck an air stair with the left wing. The aircraft then continued its circle and struck the air stair a second time with the radome and the fuselage abeam the captain's seat. The aircraft came to a stop at this time. After the plane stopped I looked down and saw that the hydraulic pressure in the accumulators was at zero psi. I then turned the hydraulic switch to the override position and the pressure pumped up into the normal range. While taxiing; the hydraulic switch had been caged in the auto mode.
While taxiing to reposition; the aircraft's hydraulic system failed followed by the loss of steering and brakes; so out of control the aircraft struck air stairs with a wingtip; turned 180 degrees; striking the stairs again with the radome.