Qeshm Air flight 1202 from Tehran-Mehrabad Airport, Iran, performed a forced landing at Mashhad when the left main landing gear failed to deploy prior to landing. The aircraft, a Fokker 100, departed Tehran at 16:39 (13:09 UTC). It was descending towards the destination of Mashhad at 17:38 when the undercarriage was selected down. However, the left hand main gear did not deploy. The flight entered a holding pattern and the flight crew worked the related checklists. Twenty minutes later the flight performed a low pass over the runway and entered another holding pattern. The left main gear remained up. A forced landing was carried out on runway 31R at 18:28. The aircraft swerved to the left and departed the left side of the runway, coming to rest between runway 31R and 31L. An evacuation was carried out. The next morning the left wing was lifted by a crane. When the lifting belt broke, the wing hit the ground again, causing serious additional damage. Probable causes: The main cause of this accident was entering foreign contamination to hydraulic system by maintenance activities during C-Check which caused damage on blockage hydraulic flow in restrictor check valve. The screen filter near hydraulic restrictor check valve was damaged by reflected force of Pollution and sediment available in the hydraulic system between and caused blockage the nozzle downstream to down lock LH landing gear mechanism. Contributing Factors: – Insufficient surveillance on maintenance operation of aircraft. – Lack of enough experience for Qeshm Air maintenance personnel