BE20 flight crew reported the left engine's performance was deteriorating inflight and the Captain; believing there to be possible fuel contamination; performed an inflight engine shutdown and restart. The right engine began to have abnormal operations after the left engine began to operate normally; and the flight crew opted to divert. After landing; Maintenance found a contamination in the fuel and filters that was determined to be the cause.
Synopsis
BE20 flight crew reported the left engine's performance was deteriorating inflight and the Captain; believing there to be possible fuel contamination; performed an inflight engine shutdown and restart. The right engine began to have abnormal operations after the left engine began to operate normally; and the flight crew opted to divert. After landing; Maintenance found a contamination in the fuel and filters that was determined to be the cause.
Narrative
At FL230 I noticed a decrease in torque on the number 1 engine. After troubleshooting and 3 minutes of monitoring conditions of engine; slow continued deterioration; I requested a descent to 14;000 from ZZZ Center and stated erratic engine indications for need for descent. I was suspecting possible fuel contamination with possible ice; so requested lower for higher OAT and increased single engine performance in case of failure. At 16;000 ft. the left DC GEN and left FUEL PRESS annunciator lights illuminated which caused me to initiate memory items for an in-flight engine shut down. Upon reaching 14;000 ft. the engine was feathered and the pilot was perplexed; I opted for a restart attempt. The engine restarted and ran at normal power. I than requested to climb back to 16;000 ft. for better communications. At 16;000-ft. level off; the right engine; opposite; started fluctuating at 1640 - 1790 torque with a full power lever knob increase required to maintain this power to match the left; now operating normal engine. I requested a divert from planned destination of ZZZ1 to ZZZ. Reason for requested divert; erratic engine indications. After landing; all run-ups showed normal indications. After further investigations; the operator of aircraft discovered a white; crystalized; gelatinous goo in both fuel filters and engine driven fuel screens. After lab testing; it was determined DEF (Diesel Exhaust Fluid) to be the cause. More than likely added to a Prist tank in error.
Second reporter narrative
After diverting to ZZZ; original destination ZZZ1; the pilot reported losing power on the left engine and performed a manual engine shutdown. The pilot descended and performed a successful restart of the left engine. All engine perimeters appeared normal. Within a short time; the right engine began to lose power. The pilot elected to divert to ZZZ and landed without further incident.Upon inspection of the aircraft's fuel system by the Company's in-house maintenance team; it was noted airframe and discharge paper filters had a crystal-like white substance on the paper filter. The airframe filters had what looked like a dark grey slimy material. Nothing concerning was noted in the fuel tanks. Fuel samples were visually tested for water which appeared negative. The filters were later sent to an independent vendor for testing. The fuel and filters were positive for Diesel Exhaust Fluid contamination that resulted in the clogging of the fuel filters; and subsequent engine performance loss.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.