Incident Overview
During takeoff, the flight crew reported that the landing gear would not completely retract. Only the right main landing gear retracted while the gear motor continued to run; the left main and nose gear remained extended. When the crew cycled the landing gear handle to the down position, the gear motor stopped, but the right main landing gear failed to extend. After a second cycle, the right main still did not extend. The crew attempted to use the emergency gear extension checklist, but the emergency extension handle was very hard to move and then seemed not to engage anything. The crew performed an emergency landing with the right main gear retracted.
During the subsequent recovery process, a bolt that attaches the clutch shaft and nose gear drive sprocket was found lying in the belly of the airplane.
Maintenance History
Examination of aircraft and maintenance records revealed that the airplane had undergone a phase inspection approximately one month before the incident. This inspection involved replacement of the landing gear retraction gear box and clutch. The records indicated that the item was removed and an overhauled unit reinstalled in accordance with the manufacturer's maintenance manual.
The maintenance technician who performed the work stated that he used the manufacturer's maintenance manual as a step-by-step guide. He reported that "all parts, nuts, bolts, cotter pin, etc, were intact when the final inspection was completed. New cotter pins were used to safety these items." After installation, the assembly and operational checks were inspected by his lead mechanic and an inspector. The gear was cycled approximately 12 to 15 times, and the cavity was vacuumed before the final inspection and floor panels reinstalled.
At the time of the incident, the airplane had flown a total of 21.9 hours, including 35 landings, since the phase inspection.
Subsequent Findings
Nine days before the emergency landing, another flight crew reported an inability to retract all three landing gear during a go-around procedure. An examination revealed that a mechanic had removed the center and right floor boards and visually inspected the landing gear limit switches and the engagement of the emergency extension disconnect assembly. The inspection of limit switches consisted of visually checking the mount bracket and the security of the switches and wiring. The mechanic also visually inspected the wiring to the gear motor and the engagement of the emergency extension disconnect, and engaged and disengaged the "J" hook several times, finding it operated normally. The visible portion of the nose gear chain was examined for general condition. The floorboard panels were reinstalled, and the gear were cycled three times in five minutes, followed by four more cycles. All functional tests were normal, and the airplane was returned to service. At the time of this inspection, the airplane had flown 11 hours since the phase 4 inspection, which included 17 landings.