On March 9, 2005, at 1230 mountain standard time, a Cessna A185E, N4530F, ground looped during the landing roll at Marana Regional Airport, Tucson, Arizona. The airline transport pilot and four passengers were not injured. The airplane sustained substantial damage. The pilot, who was also the registered owner of the airplane, was operating the flight under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot departed from Stellar Airpark, Chandler, Arizona, at 1200 for the personal flight, and was landing at his destination when the accident occurred. According to the pilot, he called the Marana universal communications (UNICOM) frequency prior to landing and prepared to land on runway 12. He performed a wheel landing, and as the tailwheel touched down, the airplane began veering to the left. The pilot applied right rudder, followed by the application of the right brake, attempting to stop the leftward veer. The airplane continued to the left and ground looped. The right main landing gear sheared off, proceeded by ground impact of the right wing, right elevator, and right stabilizer. As the pilot exited the airplane, he noted that the winds were calm. The pilot reported about 2,800 hours in airplanes equipped with conventional landing gear, with about 200 hours in Cessna 180 and 185 airplanes. The pilot reported about 17,080 hours total flight time with 105 in the accident airplane make and model. An aviation maintenance technician (AMT) examined the airplane following the accident. The initial examination revealed that the tailwheel would lock when positioned to the right; however, when positioned to the left, it would not lock. Instead, the tailwheel would free caster. The tail wheel assembly was removed for further examination of its internal components. The Federal Aviation Administration coordinator participated in the disassembly and inspection of the tailwheel on March 15, 2005, and submitted a written statement. The inspection revealed that the tailwheel-locking collar had not been installed on the tailwheel fork assembly. The purpose of the tailwheel-locking collar is to prevent uncommanded swerve or aircraft direction change during takeoff and landing. It was not apparent that the tailwheel-locking collar had not been installed until the tailwheel was disassembled. The tailwheel-locking bellcrank was installed on the tailwheel bracket assembly and is designed to engage with the tailwheel-locking collar to lock the tailwheel. In the cockpit, the tailwheel-locking control and the tailwheel-locking bellcrank operated normally. However, the tailwheel could not be locked without the tailwheel-locking collar installed. The steering notch on the tailwheel steering arm assembly that enables the tailwheel to steer the airplane was worn out. The worn tailwheel steering arm assembly allowed the tailwheel to be turned about the steering axis with only light force applied by hand. The worn tailwheel steering arm assembly would allow the tailwheel to swivel without command during a swerve. Review of the airplane's logbooks did not reveal when the tailwheel assembly was last disassembled. The last check on the tailwheel was during the annual inspection on December 15, 2004. According to the approved airplane maintenance manual, the tailwheel steering is to be checked every 200 hours of operation or at the annual inspection.