 With the lever no longer restrained by the safety system, the copilot continued to hold the right throttle fully open.The combination of the right engine at full thrust in reverse and the left engine still at normal forward take-off thrust caused the aircraft to roll violently to the right and descend into the ground.In the subsequent investigation it was discovered that the flight crew had not been trained for such an occurrence as the aircraft's manufacturer, Fokker, had judged the failure mode to be so remote a possibility that training for recovery was not necessary.