What happened
The flight crew reported encountering icing conditions while cruising at 6,000 feet mean sea level. They utilized the aircraft's de-ice and anti-ice systems to mitigate the hazard. After descending below the layer of precipitation and confirming they were clear of icing conditions, the crew deactivated these systems. The captain inspected the propeller spinners and observed a minimal amount of ice buildup, which he deemed insignificant. He then turned off the continuous ignition system.
Shortly thereafter, while on final approach approximately 1,000 feet above ground level and one to 1.5 miles from the airport, the right engine lost power without warning. The co-pilot feathered the right propeller, and the crew continued the approach. However, at approximately 200 feet above ground level, the left engine also experienced a flameout. The aircraft was landed safely without further incident.
The investigation
A post-accident examination revealed ice on the ground directly beneath the wings of the aircraft. Investigators found no evidence of mechanical failure or fuel contamination that could explain the power loss. Records indicated that this specific aircraft model had a history of engine flameouts caused by ice buildup and subsequent release from the propeller spinners.
Findings
The ignition switch on the aircraft was labeled with 'NORM', 'CONT', and 'OVRD' positions. To achieve continuous ignition during flight, the switch must be placed in the 'OVRD' position. The flight manual did not contain a specific warning instructing pilots to use continuous ignition when operating in icing conditions. It is likely that ice accumulated on the spinners after the anti-ice systems were deactivated and was ingested into the engines, causing the flameouts.
Safety message
Pilots should be aware that even minimal ice buildup on propeller spinners can lead to engine flameout if the ice is released during operation. Continuous ignition may be necessary in icing conditions, even after visual clearance of precipitation.