On March 3, 2001, about 1452 eastern standard time, a Cessna 402C, N108GP, registered to a private individual, leased to and operated by Safe Air International, Inc., dba Island Express as Sandy Isle Flight 108, experienced a loss of directional control and subsequent collapse of the right main landing gear during the landing roll at the Fort Lauderdale/Hollywood International Airport, Fort Lauderdale, Florida. Visual meteorological conditions prevailed at the time and a defense visual flight rules (DVFR) flight plan was filed and activated for the 14 CFR Part 135 scheduled, international, passenger flight. The airplane sustained minor damage and there were no reported injuries to the airline transport-rated pilot or eight passengers. The flight originated about 1352, from Marsh Harbor, Bahamas. The pilot stated that during the approach to runway 27L, all gears were extended and locked as evidence by illumination of the gear down and locked lights. He reported that the wind was from the southwest at 15 knots with no gusts and touched first with the left main landing gear followed by the right main then nose landing gear. During the landing roll while almost stopped, "I felt like a blown tire, right wheel zig zag and suddenly I could not control turn to the right and landing gear collapse." The airplane came to rest upright (See photograph 1); minor damage was noted to the right wing tip. During recovery of the airplane, the right main landing gear wheel assembly was noted to be rotated nearly 90 degrees (See photograph 2). Additionally, the upper and lower link assemblies were separated from each other; the attach hardware for them remained in the upper link assembly. Examination of the airplane by an Federal Aviation Administration (FAA) airworthiness inspector revealed a AN175-20 bolt with attached castellated nut and associated washers and bushing pulled through the lower link assemby of the right main gear on the nut end of the bolt. Additionally, the inboard lower portion of the right main landing gear tire exhibited evidence of scrubbing due to contact with the ground (See photographs 3 and 4). The bolt and associated hardware (See photograph 5), and the right main landing gear actuator were retained for further examination. A copy of the FAA inspector statement is an attachment to this report. The right main landing gear actuator was manufactured by Teijin Seiki Company, Ltd., as part number 1521200-9. Bench testing of the actuator revealed the unlocking pressure was greater than specified when tested 5 separated times; the unlocking pressure measured between 450 and 525 psi. The specified unlocking pressure is between 250 and 400 psi. No leaks were noted during the pressure testing. Disassembly of the actuator revealed that one of the four lock keys (part number (P/N) 1521210-5) was improperly installed (See photograph 6), resulting in a rolled edge on the inside diameter of the cylinder end P/N 1521203-1 (See photograph 7). Additionally the cylinder end was not bottomed on the cylinder barrel P/N 1521201-3) per instructions found in the overhaul manual; according to repair station personnel this had no effect. An excerpt from the maintenance manual depicting the correct installation of the lock key is an attachment to this report. Cessna Service Bulletin MEB91-12, dated December 20, 1991, pertaining to functional testing of landing gear actuators with a mandatory accomplishment every 12 months, indicates in part, "Replace actuator if it does not meet the unlock pressure requirement...." The service bulletin was accomplished last on December 29, 2000, as depicted in a Service Bulletin Compliance Record. Copies of the service bulletin and the Service Bulletin Compliance Record are attachments to this report. Examination of the retained bolt and attached hardware by the NTSB revealed the outside diameter of two washers that were installed on the nut end of the bolt were reduced/failed; and exhibited evidence of being bent towards the castellated nut (See Photograph 8). The washers measured approximately .023 inch thick (See photographs 9 and 10). The washer that was installed beneath the bolt head measured approximately .061 inch thick (See photograph 11). Cessna Service Information Letter ME83-37, dated November 23, 1983, titled, "Main Landing Gear Scissor Washer Replacement", which is non-mandatory, recommends to replace the two outer washers on the main landing gear scissor link for improved service life and main gear wheel alignment retention. There was no record of compliance with the non-mandatory service information letter in the maintenance records. The thickness of a washer specified in the service information letter is approximately .065 inch (See photograph 12). A copy of the service information letter is an attachment to this report. Review of the maintenance records by the FAA airworthiness inspector revealed no serviceable tag for the incident actuator. The actuator was installed in the airplane on August 3, 1996, and had accumulated 5,993.4 hours and approximately 4,500 cycles since installation at the time of the incident. The landing gear was rigged and operationally checked last on October 21, 2000, which is accomplished every 400 hours or 12 months; the airplane had accumulated approximately 345 hours since then at the time of the incident. The landing gear which is inspected every 180 hours during a "C" check, was signed off last on February 11, 2001. The airplane had accumulated approximately 76 hours since the inspection at the time of the incident. The Cessna Progressive Care Program does mention to inspect the main landing gear torque links; however, the FAA approved inspection program for the operator does not mention to inspect the main landing gear torque links. A copy of the FAA approved "C" inspection performed last, excerpts from the maintenance records, and an excerpt from the Cessna Progressive Care Program are attachments to this report. The airplane minus the NTSB retained right main landing gear actuator was released to the airplane owner, Dave Bettencourt, on March 23, 2001. The retained right main landing gear actuator was released to Mayra A. Horna, Secretary and Treasurer for Island Express, on October 23, 2001.