"Ladas" ran about after losing the rack rail before hitting a left-hand curve. Here it derailed and fell over the side of the mountain. The two carriages accelerated to a speed at which the automatic brakes were triggered (). These brakes brought both carriages to a stand safely. One of the passengers, Ellis Griffith Roberts of Llanberis, on seeing the driver and fireman jump from the locomotive did likewise. Falling to the ground, he sustained a serious injury to his leg, which later had to be amputated, and he died.