Date: 201901
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Aircraft component: Brake System
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying
Reporter qualification: Flight Crew Private
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Runway
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control; Flight Crew Rejected Takeoff; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During a standard departure from ZZZ; my aircraft veered to the left off of Runway XXL into the gravel apron between the runway and Taxiway A coming to a stop on Taxiway C.Preflight check was normal; refueling went normal; run-up was normal; contacted Ground from the fuel pump and was given taxi instructions to [Runway] XYL via E; and Alpha. Taxi went normal. Contacted Tower that I was holding short of [Runway] XYL at A. I was then given clearance to take off on Runway XYL with a left turn out and departure to the southwest.My aircraft is equipped with 'Finger Brakes' located on the center console. I entered the runway and used differential braking and rudder; turned left to line up with the runway centerline. Once lined up but still rolling; I gradually applied full power and some right rudder. As the plane quickly moved forward; it started to veer to the left. I applied more right rudder until I had all right rudder and still only managed to decrease left turn.The plane left the runway between [taxiways B and C]; but once on the gravel came more to the right and I was able to avoid any runway lights or signs. Its momentum carried me onto the Taxiway C intersection in between Runway XYL and Taxiway A where I stopped. I contacted the Tower and advised them that I had aborted the takeoff and requested taxi back to parking. During the taxi back; the aircraft had a distinct tendency to turn left. When I put my hand on the brake levers; I felt a misalignment between the levers. Further inspections showed that the finger knob on the left lever had jammed behind the finger knob on the right lever. This caused the left brake to drag while taxiing enough to cause the veering tendency. Once they were unjammed; normal steering resumed. I taxied to parking and performed a detailed inspection of the aircraft. With the exception of some dings to the paint on the rear horizontal tail plane; no other damage was noted. With this issue in mind; I continued my flight uneventfully with several landings and takeoffs with no problems.After returning; I secured the aircraft and began to engineer replacement parts to prevent this issue again. I manufactured two replacement knobs that will not be able to jam and repeat this problem. The following week; I performed repairs to the paint dings. I also replaced both finger brake knobs and exercised the finger brakes several times and am confident this problem will not be repeated.




Synopsis: Experimental aircraft pilot reported a brake malfunction and runway excursion during takeoff roll.