What happened
On June 17, 2017, during a flight, the pilot of a De Havilland Canada DHC-8-Q400, registration SP-EQE, reported significant issues with the aircraft's aileron controls. The pilot noted that to maintain straight flight without banking, the control column had to be deflected 5 degrees to the right, and the aircraft was not responding correctly to control inputs. Following this report, the aircraft was grounded for inspection.
On June 18, 2017, during a maintenance inspection at the LS Technics technical base, technicians discovered a severe failure in the left wing's aileron control system. Specifically, the internal lower control cable (P/N 82742408-003) located between pulleys Y-194 and Y-200 had suffered a partial breakage that amounted to a functional destruction of the component. The remaining unbroken strands of the cable were under no tension, rendering the cable effectively severed.
The investigation
The PKBWL investigation reviewed the maintenance history and flight logs of the aircraft. Records showed that the last inspection of this specific structural area had been performed three months prior, on March 19, 2017, at which time the cables were found to be in good condition with correct tension (87 lbs). At the time the defect was discovered during the June inspection, the aircraft had accumulated 9,534 flight hours and 10,767 flight cycles.
Findings
- The primary cause of the incident was the fatigue failure of the left aileron control cable.
- The failure occurred between the last scheduled inspection and the maintenance check following the pilot's report.