Accident Summary
A Learjet 35, registration LV-ZSZ, was destroyed by fire after a runway excursion during a rejected takeoff at San Fernando Airport in Buenos Aires. The aircraft was on a positioning flight to Río Gallegos with two pilots on board; both evacuated safely.
Sequence of Events
During the takeoff roll, the copilot (acting as pilot-in-command) observed that the left engine's N1 reached 101%, while the right engine indicated 95%. At approximately 380 meters of ground roll, the aircraft began to veer right. The copilot decided to abort the takeoff without informing the captain. The power levers were retarded to idle, and braking was applied.
After about 980 meters of ground roll, the right engine's N1 decreased to 30-40%, while the left engine remained at 101%. The captain then assumed control and briefly deployed the thrust reverser as the aircraft departed the runway to the right. Continuing across a grassy area, the aircraft struck a drainage ditch 80 meters from the runway, losing its landing gear. It slid several dozen meters before coming to rest and bursting into flames. Both pilots evacuated the aircraft safely; the aircraft was destroyed by the subsequent fire.
Probable Cause
The official investigation determined that the most likely cause of the uncommanded acceleration and overspeed was contamination of retained particles within the fuel control unit (FCU). This contamination was a short-lived, random condition, as evidenced by the left engine regaining normal power lever response after about 30 seconds. The accident resulted from a combination of factors: the uncommanded acceleration of the left engine at the start of the takeoff run; the initial lack of response of the left engine to power lever inputs; the crew's difficulties in managing an unusual condition in accordance with the Airplane Flight Manual; ambivalence in regulations authorizing a copilot in an aircraft requiring two pilots; and duality in the application of safety standards. Additionally, the state of the runway 05/23 protection zone at San Fernando Aerodrome contributed to the severity of the accident, though it was unrelated to the initiating event.