Date: 202108
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Baron 55/Cochise
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Reciprocating Engine Assembly
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Private
Human factors: Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Flying from ZZZ to ZZZ1 takes approximately four hours in this aircraft. Normal fuel management requires the takeoff and the first hour on the mains; then two hours on the auxiliary tanks; finishing the final hour on the main tanks. There was a tail wind that day so the distance traveled on each set of tanks increased. Just prior to ZZZ [VOR] the final fuel switch was made from the auxiliary tanks to the mains. Approximately twenty minute later; the left engine started to surge. Scanning all engine monitoring instruments showed normal temperatures; RPM; fuel flow; and manifold pressures being matched by each engine. The engine returned to normal cruise profile for about fifteen to twenty seconds; then surged violently. Thinking it may be a fuel contamination problem; I switched the left tank back to the auxiliary tank knowing that there was approximately fifteen minutes of fuel remaining. The left engine continued to surge and RPM of the left engine would not go above fifteen hundred RPM. I contacted Approach; apprised them of the situation and requested vectors to the closest airport; which happened to be ZZZ2. They vectored me towards ZZZ2 when the engine decided that it had had enough. The aircraft was handling erratically; so I decided to cage the engine and make the approach and landing on the remaining right engine; I had seven thousand feet to descend to airport elevation with only ten miles to accomplish it; so I circled the airport to the south to keep a right hand pattern into the airport. There was a successful landing and difficult taxi to tie down where I was met with the local [officials] and rescue squad. An inspection a couple days later with a certified A&P found that there was a leak around the filler cap on the left main tank which allowed the low pressure over the wing to suction out the entire tank. The main filler caps are hid from the pilot's view by the engine nacelle. I believe that after three and a half hours of flying through IMC up to the point of the incident weighed heavily on my initial decision not to cage the engine; but to try to troubleshoot problem and on this particular aircraft; the fuel gauges are obscured by the power levers and my initial scan failed to see the amount remaining in the left main tank.




Synopsis: Pilot reported performing an in-flight engine shut down due to a suspected fuel issue and conducted a precautionary landing.