The Falcon 20 had a night stop at Port-Harcourt (PHC), and departed at 06:37 UTC Lagos (LOS). The takeoff was normal, but after passing 1500ft when carrying out the “after takeoff” checks the crew noted that there was a red landing gear warning light indicating that the left main landing gear was not properly closed. The crew recycled the landing gear twice but the problem persisted. A third recycling was carried out with the landing flaps extended to 10 degrees. After this, the warning light went off and the flight continued normally cruising at FL220. The aircraft commenced its initial descent at about 07:15 UTC. The aircraft was cleared for an ILS approach to runway 19R. Close to the localiser intercept, the gears were lowered and the landing gear indicators showed that the left main gear was not deployed. The landing gears were recycled, but to no avail. The crew then proceeded to the area west of the field, climbed to 5000ft and carried out the “Emergency and Abnormal checklist”-Landing gear will not extend (Procedure B). Numerous attempts of this procedure were made but the left main gear failed to lock down. The crew then carried out a low fly past for a visual observation of the landing gears. The crew also tried side-slipping the aircraft to shake the left landing gear down, but with no positive result. An emergency was declared and after burning the fuel in the main tanks and the landing was made with the two gears extended. The aircraft touched down and veered to the left side of the runway and ran into the runway shoulder. PROBABLE CAUSE: “The accident was caused by the fatigue failure of the door actuator bellcrank of the left main landing gear due to an improper rigging of the door actuator push rod in the door mechanism.”