On 30 December 2011, a Bombardier DHC-8-102 aircraft, registered VH-QQA, was being operated on a scheduled passenger service to Cairns, Queensland. During the landing, the crew perceived that the aircraft decelerated much quicker than they expected given that reverse thrust and landing gear brakes had not been selected. A subsequent inspection of the aircraft found nothing to explain the perceived problem, and a review of the flight recorder data indicated that there was no abnormal operation of the engines or propellers, and that reverse thrust had not been used.
What the ATSB found
Although unrelated to the reported occurrence, subsequent inspection of the aircraft identified a design problem within the aircraft’s power lever control quadrant. The problem related to the friction device within the power levers and its interaction with the flight idle gate, which was designed to prevent the power levers from going into the ground range in flight. When the friction knob was wound to the full out (friction off) position, the flight idle gate was lifted by contact between the friction device and the flight idle gate. That action rendered the flight idle gate inoperative.
The design problem only applied to the first 39 DHC-8-100 aircraft that were manufactured; subsequent aircraft were manufactured with a modified design. The aircraft manufacturer introduced a service bulletin requirement in 1986 to retrospectively modify these 39 aircraft, but the service bulletin omitted a requirement to modify or replace a specific part, which resulted in the bulletin being ineffective.
What has been done to fix it
Once informed of the design problem, the aircraft manufacturer took prompt action to address the issue. It issued a service bulletin to modify the relevant part, and this action was subsequently mandated by Transport Canada and the Civil Aviation Safety Authority of Australia.
This investigation highlights the importance of crews reporting occurrences and other perceived problems. Although in this case the actual event reported by the crew was not serious, and no problems relating to the aircraft or crew performance leading to the perceived event were identified, the subsequent investigation did identify a safety issue in the design of the aircraft.