During the approach, the flight crew observed an indication that the right main landing gear was not in the ‘down and locked’ position. After completion of the emergency checklist items, the

indicator continued to show that the right main landing gear was unsafe. An emergency was declared and the aircraft made an uneventful landing. An investigation by the operator revealed

that a grease nipple, released from the right main landing gear lock link assembly, had become lodged on the eye end of the landing gear downlock actuator, preventing the lock from operating

correctly. As a result of this incident the operator has introduced several measures to minimise the possibility of a recurrence.