An Antonov 12B, ST-AQQ, sustained substantial damage in a landing accident at Heglig, Sudan. The airplane suffered an undercarriage collapse and damage to the no. 1, 2 and 4 propellers. There were no injuries. Magal Flight 100 departed Khartoum (KRT), Sudan at 07:38 with 13 tons of cargo on board, bound for Heglig, Sudan. The airplane touched down on the gravel, 16 meters short of the runway. It struck concrete blocks, runway lights and then bounced. It impacted the runway nose-first. The captain ordered the props to be unlocked so they would go into ground fine pitch. However, the throttle of engine no. 4 was still at 42% with the other engines below 20%. An asymmetric thrust condition occurred as the no. 4 engine consequently did not go into ground fine pitch. This caused the plane to drift to the left side. It passed over a gravel road, then lost the left main landing gear, turned to left and broke the right hand main landing gear and nose gear before it stopped. Main Cause: 1- Landing short of the runway beginning. 2- The flight engineer unlocked props I, II, III at throttle position < 20ø UPRT and No IV engine at 40ø UPRT. Contributory Cause: - Unrectification of nose wheel and main landing gear crack as recommended by the manufacturer.