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After arriving in the circuit area the pilot extended the landing gear and obtained the correct down and locked indications. The right main gear leg subsequently collapsed during the landing roll. The retract actuator trunnion bearings had collapsed, allowing excessive movement of the actuator in its mount. This resulted in insufficient travel of the actuator to fully engage the downlock. Two separate occurrences involving unsafe landing gear indications, which had been corrected in flight by recycling, had been reported to the operator's maintenance staff prior to the accident. The maintenance staff, unable to duplicate the defect on the ground, had adjusted the downlock switch. Those adjustments finally resulted in the switch jamming in the closed position, giving a safe indication. The downlock switch has two functions, providing independent safe/unsafe indications of the lock and, in series with the nose and left leg switches, removal of electrical power to the hydraulic pump when the three downlocks are sensed in a locked condition. On the accident flight, with the right downlock switch jammed in the closed position, hydraulic pressure was terminated when the left and nose gears locked down. As the lock function of the right gear lock was compromised because of the failed trunnion bearings, the leg collapsed under the landing loads. Investigation of the aircraft maintenance requirements determined that the landing gear actuator trunnion bearings had been incorrectly identified as sealed bearings requiring no lubrication. The bearings fitted to the aircraft were of the unsealed type, with a requirement for lubrication every 1000 landings or 30 months. Safety Action As a result of the investigation into this occurrence, two other B200C aircraft from the same operator were found to have similar unsealed bearings fitted to the main landing gear actuator trunnion bearings. The operator has taken action to amend the aircraft inspection schedule to include lubrication of unsealed bearings and initiated a retirement life program for all sealed bearings. The Bureau of Air Safety Investigation issues the following Safety Advisory Notice. SAN 960030 The Bureau of Air Safety Investigation suggests that the Civil Aviation Safety Authority consider publishing an appropriate educational article detailing the circumstances of this occurrence and highlighting the need to correctly identify the various types of bearings, and their lubrication requirements, in all aircraft components.
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General details
Date: 11 May 1994 Investigation status: Completed 
Time: 15:30 EST  
 Investigation type: Occurrence Investigation 
 Occurrence type: Wheels up landing 
Release date: 05 August 1996 Occurrence class: Operational 
Report status: Final Occurrence category: Accident 
Aircraft details
Aircraft manufacturer: Beech Aircraft Corp 
Aircraft model: B200C 
Aircraft registration: VH-AMM 
Sector: Turboprop 
Damage to aircraft: Substantial 
Departure point:Brewarrina NSW
Destination:Dubbo NSW
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Last update 21 October 2014