A Non-Injury accident occurred on the MMU. No. 003-0 Section during second or retreat mining. The accident occurred in the # 3 entry, 50'ft. inby Survey Station 4274 on the 1 Rt. Panel which caused the # 1 MRS to be caught by the mine roof which had fallen above anchorage of the primary roof support. MSHA was immediately notified about this accident or event that occurred.