Date: 201303
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Caravan 208B
Operator: Air Taxi
Operating under: Part 135
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ground ZZZ
Aircraft component: Brake System
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Pilot Not Flying
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Anomaly: Aircraft Equipment Problem Critical; Conflict Ground Conflict; Critical; Ground Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Regained Aircraft Control; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Gate; Flight Crew Took Evasive Action; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: The pilot flying and I arrived at the airplane approximately 1 hour and 15 minutes to prepare for the flight. The aircraft had 1;550 LBS of fuel. The trip sheet showed a full load; 8 passengers; along with their listed weights. The luggage was brought out to us without manifest; so we used the scale onboard the aircraft to get exact weights of luggage for proper loading as we knew we would be close to max takeoff weight. Using the passenger weights off the trip sheet; we came up with assigned seating for the passengers to ensure we were within center of gravity limitations. Per our calculations; the ramp weight came out to be 9;062 LBS exactly. Weight and balance was completed and showed that we were well within center of gravity limitations. We determined we would need to burn some extra fuel in order to be below maximum landing weight upon arrival; more precisely; we would need to be indicating 988 LBS of fuel before landing. The pilot flying briefed the passengers that we would be starting up but not moving for a period of approximately 30 minutes to burn some extra fuel for weight purposes. While waiting; we ran through all first flight items to stay engaged (though it was not the first flight of the day). We did not burn as much fuel as we had hoped before moving; but decided to proceed for taxi and takeoff as we could burn fuel at a faster rate in flight and were below takeoff maximum weight limitations. We were parked at the gate; offset approximately 50 FT to the right of center-line; but facing straight to the taxi lane. The space in front of us to the taxi-lane was free from vehicles and obstructions. On the far side of the taxi lane parked against the grass were the usual ground service vehicles. The pilot flying was sitting left seat and had the controls; I was sitting right seat and was performing the pilot not flying duties. Taxi checklist was completed; taxi clearance acquired; and the pilot flying released the parking brake. The first turn we made was a slight left turn to get lined up with the taxi-lane center line on the way out of parking. We very gradually and slowly taxied through the centerline. I brought the centerline deviation to the pilot flying's attention to which he replied that he was not getting any steering response. We were getting very close to the ground service vehicles and started turning even further to the left towards them. I was bringing my feet up to the pedals to assist with brakes as I saw we were in full reverse. This action turned us even further left; nose to nose with a service truck still not completely stopped. We had little to no braking response. I started saying 'shut down' repeatedly; and less than a second later the pilot flying pulled the condition lever to cut off and we came to a stop approximately 1-2 FT from the service vehicle. The pilot flying pulled the parking brake as I got out and chocked the left wheel. I unloaded the passengers and brought them to the terminal. In the very quick walk around to get the wheel chocks and tail stand; I made a few key mental notes. The rudder lock was disengaged; the rudder pedals were indicating a left turn (left pedal towards the firewall); the left tire appeared abnormal (maybe low tire pressure). In the time following; it seemed the left tire had no abnormalities. Mechanical inspection found no abnormalities. The following is merely speculative; but a theory I came up with after talking to an A&P. We frequently park at an airport with a 3 degree slope to the ramp and leave the parking brake on over night and for extended periods of time. According to the mechanic; corrosion can build up in brake lines and contribute to the brakes being held in a fixed position. If the fixed position held more on the left side than the right; this would be consistent with a left turn as well as a lack of braking.




Synopsis: Cessna 208B veered left during initial taxi; indicating the crew had no nosewheel steering coming within feet of a service vehicle.