A Learjet 35A, LV-ZSZ, was damaged beyond repair in a takeoff accident at San Fernando Airport, Argentina. Both crew members escaped uninjured. In preparation for a positioning flight to R¡o Gallegos the crew failed to connect an inverter, a component of the electrical system that converts the direct current from 28V to an alternating current of 115V, prior to starting engine no.1. This was then rectified. At 09:34 the aircraft taxied to the threshold of runway 05 for departure. The copilot was Pilot Flying while the experienced captain was Pilot Monitoring. Takeoff clearance was received at 09:40 and the power levers were advanced. During the takeoff roll the copilot noticed that the no.1 engine N1 reached a value of 101% instead of 95% like the no.2 engine. At that point the aircraft had already traveled 380 m. It began to drift to the right of the runway centreline. The copilot decided to abort without voicing his intentions. he brought back the power levers to idle and began applying brakes. At this point, LV-ZSZ had traveled approximately 980 meters from the start of the take-off run. The right engine power decreased to 30-40% N1 while the left engine continued at a value over 101% N1. The captain then took over control. Differential braking was applied to steer the aircraft back towards the runway centreline. Thrust reversers were deployed briefly but the aircraft ran off the side of the runway. The aircraft impacted with a ditch located 80 meters from the runway, causing the undercarriage to break away. After coming to rest with both engines now at 20% N1, the engine were shut down. As a result of the impact, part of the left tip tank fuel tank had separated, causing a fire that destroyed the aircraft. The most likely cause of the uncommanded acceleration and subsequent overspeed condition was a contamination of retained particles present within the fuel control unit (FCU). The contamination was a short-lived random condition, as evidenced by the fact that after about 30 seconds the power lever regained control of the left engine. Conclusions of the analysis (translated from Spanish) On a general aviation flight, during the take-off run, the LJ35 LV-ZSZ suffered a runway excursion on the right side, and a subsequent aircraft fire. The accident was due to the combination of the following factors: – The uncommanded acceleration of the left engine at the start of the take-off run; – The initial lack of response of the left engine to the requests of the corresponding power lever; – The difficulties of the crew in managing an unusual condition of the aircraft in accordance with guidelines established in the AFM; – The ambivalence in the existing regulations for the authorization of a co-pilot in an aircraft that require two pilots for certification; and – The duality in the application of safety standards allowed by the existing normative regulations. Although unrelated, the state of the runway 05/23 protection zone at the San Fernando Aerodrome contributed to the severity of the accident.