Date: 201404
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Super King Air 200
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Passenger
Flight phase: Taxi
ATC / advisory: CTAF ZZZ
Aircraft component: Normal Brake System
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Confusion; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Ground Event / Encounter Loss Of Aircraft Control; Ground Event / Encounter Object; Ground Excursion Taxiway
Detector: Person Flight Crew
When detected: Taxi
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Ambiguous

Narrative: The winds were reported 230 degrees at around 25 KTS sustained; gusting to approximately 30 KTS. I loaded the passengers and set the parking brake. I completed the required checklist and started the engines normally. After listening to the ATIS I determined Runway 20 would be the most suitable runway for departure. I released the parking brake and checked the brakes per the checklist. Taxiing from the ramp to the parallel taxiway to Runway 20; the brakes worked fine. Taxiing down the parallel taxiway of Runway 20; the strong tailwinds were beginning to accelerate the aircraft; so I opted to feather both engines to slow the aircraft down; as well as; to comply with the required feather check of the engines. I also began to apply light brake pressure to assist in deceleration. Upon applying brake pressure; I noticed the left brake felt a little soft so I began to pump the left brake thinking it would build up pressure. Realizing that I may be having a mechanical issue; especially with the strong tailwinds pushing me down the taxiway; I brought both propellers out of feather. The aircraft immediately accelerated as the propellers returned to idle with the strong tailwinds and I instinctively began to apply both brakes. The left brake provided no braking action whatsoever although the right brakes did; turning the aircraft to a right angle and heading for the edge of the taxiway. I then quickly applied full reverse thrust on both engines in an effort to stop along with full brake application of both pedals. I felt normal brake pressure on the right pedal; while the left pedal pressed easily to the floor. As indicated by the tire marks left on the taxiway; only the right brakes actually applied. The strong winds were now pushing on the right side of the vertical stabilizer (tail) acting like a weathervane compounding the situation. When I realized I was going to run off of the taxiway; I quickly feathered both propellers and pulled the condition levers on both engines to 'fuel cutoff'. The aircraft's right main gear and nosewheel went off of the taxiway into the grass; while the left main gear remained on the taxiway. As the aircraft was coming to a stop and the engines were spooling down in the feathered position; one of the right engine propellers struck a taxi light causing damage to both the propeller blade and taxi light. There were no injuries to anyone on the aircraft. I would guess that once I realized I was having a brake problem; I had only about 5 seconds before the aircraft exited the taxiway. In disbelief of what had just occurred; I pressed the brakes again and I felt brake pressures on both pedals. I can't explain why the left side did not work; but it is evident by the tire marks from only the right main gear on the taxiway that the left brakes did not apply at any time. After inspection by Maintenance; they could find no issues with the brake system. Could there have possibly been air in the hydraulic brake fluid that caused a momentary failure and as I continued to pump the pedal; it worked it through the system? It makes me wonder if there have been other similar events.I feel that this event may have been prevented if I had completed the feather check before turning the aircraft onto the downwind taxiway. This would have possibly given me more time to react with reverse thrust to bring the aircraft to a stop before exiting the taxiway.




Synopsis: While taxiing on a parallel taxiway for takeoff in strong quartering tailwinds; the pilot of a King Air B200 momentarily lost left brake functionality and exited the taxiway to the right as he was attempting to reduce taxi speed. The right main and nose gears were off the hard surface and one right engine propeller blade struck a taxi light.