On March 20, 2016, at 1646 mountain daylight time, a Cessna 172RG airplane, N6402V, landed gear up following a landing gear malfunction at Greeley-Weld County Airport (GXY), Greeley, Colorado. The pilot was not injured and the airplane sustained minor damage. The airplane was registered to and operated by Northern Skies Aviation Inc. under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions existed at the time of the incident. The flight departed at 1330 without a flight plan from Gillette-Campbell County Airport (GCC), Gillette, Wyoming, with a planned destination of Colorado Plains Regional Airport (AKO), Akron, Colorado.According to the pilot, he diverted to GXY after the left landing gear did not extend during arrival to AKO. Following unsuccessful attempts to extend the landing gear, the pilot elected to land gear up at GXY. Examination by Federal Aviation Administration (FAA) inspectors revealed the left main landing gear actuator assembly (part number 9882015-2) housing was cracked across the forward attach bolt hole. The crack allowed the actuator bore to open enough such that the piston would not engage the landing gear pivot sector sufficiently for gear extension. This failure mode resulted in the inability to fully raise or extend the landing gear, either in the normal method or with the emergency hand pump. The airplane's main landing gear was subject to FAA airworthiness directive (AD) 2001-06-06, which required inspection for cracks in landing gear pivot assemblies. This AD was accomplished for the airplane on May 25, 2001. For this incident, a crack was observed in the landing gear actuator assembly, which mates with the landing gear pivot assembly. The failed landing gear actuator assembly was originally installed with the airplane, which had a total time of 6490.1 hours. To address the need for initial and repetitive inspections of the landing gear actuator assembly, the FAA published maintenance alerts in prior years and Textron published service bulletins in 2001 and 2007. Following this incident, the FAA released Special Information Airworthiness Bulletin (SAIB) CE-17-16 for Cessna 172RG, R182, TR182, FR182, and 210/T210/P210-series airplanes. The SAIB emphasized the importance of inspecting main landing gear actuator assemblies and recommended complying with Textron supplemental inspection document (SID) 32-10-01, which directs a combination of visual, fluorescent penetrant, and eddy current inspections, depending on the airplane model. The SAIB included initial and repetitive inspection intervals, as well as recommending an inspection after an unplanned event, such as a hard landing.