Narrative:

During last portion of cruise phase at 6;500 feet MSL weather was clear air visibility okay (cavu). Had just changed back to main tanks and a few min latter the left engine began to 'rumble and miss' like it may have some issue with the fuel supply from left main tank. I was just looking at engine gauges when there was a loud bang and I saw the oil service port cover fly open and oil spewing out all over the cowling.as I retarded the throttle I noticed damage to the cowling and lots of oil spewing out when throttle was moved anywhere forward of idle. I advance the right engine to maximum expected takeoff power (meto) power and I then elected to shut down the left engine. After feathering the left engine and insuring there was no other issue requiring my attention I called the ATC facility that had been providing flight following to declare an emergency and help with selection of the nearest suitable field. The twin bonanza flies very well on one engine after the malfunctioning engine is feathered. I was able to hold 6;500 feet at meto power and began a slow turn toward the nearest suitable airport (30-35 nm distant) . The best wind runway is 8;000 feet long and 150 feet wide with fire equipment. That field was far superior to the nearest airport (25 NM north with a 4;000 foot runway and required a low level course reversal to land into the 15 to 20 knot winds) and no dedicated fire department. This aircraft has a garmin 480 waas GPS. Among the many features is the nearest p.b. Using that feature I was able to review several airports before choosing [my diversion airport]. After reprograming the garmin 480 for the new destination I proceeded direct to the RNAV/GPS FAF. My power was reduced to adjust the descent to cross the FAF a few hundred feet high and the flaps and gear were configured to approach flaps during the initial crossing and as I approached 1;200 feet AGL I extended the gear. Final flaps were extended at approximately 300 AGL. With the gear down ad full flaps this aircraft requires almost meto power to maintain the glide path in a 20 knot headwind. The landing was normal and after clearing the runway I had the fire trucks follow me to the ramp in case the shutdown generated some kind of abnormal issue. After completing the shutdown checklist and securing the aircraft I cancelled the emergency. Many thanks to the firemen and ATC for a superb job in all my requests. Hard to be hotter than hades on the ramp as the ambient temp was near 100 degrees F. Post flight inspection revealed a connecting rod bolt had failed; and the rod end impacted the crankcase and destroyed the impacted area and drove the camshaft thru the top of the engine case. This generated numerous pieces of shrapnel and considerable secondary damage. The newly overhauled propeller had all 3 blades damaged with shrapnel and the engine cowling was punctured with a few small holes in several places. Engine history. When I purchased this used engine (lycoming go 480) it did not have oil filters as part of it's original equipment. The engine had been on an oil analysis program and all parameters were 'nominal'. Before entry into service on this airframe I installed some aftermarket stc'ed oil filter mounts and the first few oil changes generated quite a bit of metal. We surmised the metal was part of what had been left behind during operations without an oil filter. The metal particles were mostly fine particles. After a couple oil filter changes and exams at 10 hour intervals the particles diminished to 'normal'. At the time of this failure the engine was approx. 150 hours past tbo. I had planned to overhaul it after the summer flying season was completed. The engine was equipped with an oil filter and had just completed an annual inspection with no metal found in the filter material. Additionally the engine was running as 'smooth as a top' when it failed with no warning. Photos from the inside of the engine revealed the crankshaft journal had not suffered from lack of lubrication. The connecting rod is barely visible and it appears that one rod bolt was bent in its respective location but the second bolt could not be seen. I surmise that the missing rod bolt failed for reasons that are not clear at this time. The shuddering and missing during the initial part of the engine failure was probably the engine balance being disturbed as each successive revolution of the crankshaft bent the remaining bolt and when it failed the connecting road detached and the crankshaft drove the rod end thru the top of the engine case. This impact on the camshaft forced it thru the top of the crankcase generating the shrapnel that impacted the three propeller blades and engine cowling. Glad I had two engines and the training necessary to use the capacity of the aircraft. No more flying past tbo. I have heard lots of stories about folks flying well past tbo with just a top overhaul or minor maintenance. In my case this engine had never suffered any damage with the exception of exhaust valve failure that did not require an inflight shutdown and did not puncture the piston or generate metal debris in the engine. A new cylinder was installed and all parameters were normal. The oil pressure (60psi at normal operating temps) was the same as it had been when the engine was originally installed. There was absolutely no indication this engine was in trouble before it failed. The other engine is already being scheduled for overhaul and whatever engine I put on this aircraft to ferry home will be overhauled before regular flying resumes.

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Original NASA ASRS Text

Title: The pilot of a Beechcraft Twin Engine Bonanza reported that the Left Engine failed during cruise flight.

Narrative: During last portion of cruise phase at 6;500 feet MSL weather was Clear Air Visibility Okay (CAVU). Had just changed back to main tanks and a few min latter the left engine began to 'Rumble and miss' like it may have some issue with the fuel supply from left main tank. I was just looking at engine gauges when there was a loud bang and I saw the oil service port cover fly open and oil spewing out all over the cowling.As I retarded the throttle I noticed damage to the cowling and lots of oil spewing out when throttle was moved anywhere forward of idle. I advance the right engine to Maximum Expected Takeoff Power (METO) power and I then elected to shut down the left engine. After feathering the left engine and insuring there was no other issue requiring my attention I called the ATC facility that had been providing flight following to declare an emergency and help with selection of the nearest suitable field. The Twin Bonanza flies very well on one engine after the malfunctioning engine is feathered. I was able to hold 6;500 feet at METO power and began a slow turn toward the nearest suitable airport (30-35 nm distant) . The best wind runway is 8;000 feet long and 150 feet wide with fire equipment. That field was far superior to the nearest airport (25 NM north with a 4;000 foot runway and required a low level course reversal to land into the 15 to 20 knot winds) and no dedicated fire department. This aircraft has a Garmin 480 WAAS GPS. Among the many features is the Nearest p.b. Using that feature I was able to review several airports before choosing [my diversion airport]. After reprograming the Garmin 480 for the new destination I proceeded direct to the RNAV/GPS FAF. My power was reduced to adjust the descent to cross the FAF a few hundred feet high and the flaps and gear were configured to approach flaps during the initial crossing and as I approached 1;200 feet AGL I extended the gear. Final flaps were extended at approximately 300 AGL. With the gear down ad full flaps this aircraft requires almost METO power to maintain the glide path in a 20 knot headwind. The landing was normal and after clearing the runway I had the fire trucks follow me to the ramp in case the shutdown generated some kind of abnormal issue. After completing the shutdown checklist and securing the aircraft I cancelled the emergency. Many thanks to the firemen and ATC for a superb job in all my requests. Hard to be hotter than Hades on the ramp as the ambient temp was near 100 degrees F. Post flight inspection revealed a connecting rod bolt had failed; and the rod end impacted the crankcase and destroyed the impacted area and drove the camshaft thru the top of the engine case. This generated numerous pieces of shrapnel and considerable secondary damage. The newly overhauled propeller had all 3 blades damaged with shrapnel and the engine cowling was punctured with a few small holes in several places. Engine history. When I purchased this used engine (Lycoming GO 480) it did not have oil filters as part of it's original equipment. The engine had been on an oil analysis program and all parameters were 'Nominal'. Before entry into service on this airframe I installed some aftermarket STC'ed oil filter mounts and the first few oil changes generated quite a bit of metal. We surmised the metal was part of what had been left behind during operations without an oil filter. The metal particles were mostly fine particles. After a couple oil filter changes and exams at 10 hour intervals the particles diminished to 'normal'. At the time of this failure the engine was approx. 150 hours past TBO. I had planned to overhaul it after the summer flying season was completed. The engine was equipped with an oil filter and had just completed an annual inspection with no metal found in the filter material. Additionally the engine was running as 'Smooth as a top' when it failed with no warning. Photos from the inside of the engine revealed the crankshaft journal had not suffered from lack of lubrication. The connecting rod is barely visible and it appears that one rod bolt was bent in its respective location but the second bolt could not be seen. I surmise that the missing rod bolt failed for reasons that are not clear at this time. The shuddering and missing during the initial part of the engine failure was probably the engine balance being disturbed as each successive revolution of the crankshaft bent the remaining bolt and when it failed the connecting road detached and the crankshaft drove the rod end thru the top of the engine case. This impact on the camshaft forced it thru the top of the crankcase generating the shrapnel that impacted the three propeller blades and engine cowling. Glad I had two engines and the training necessary to use the capacity of the aircraft. NO more flying past TBO. I have heard lots of stories about folks flying well past TBO with just a top overhaul or minor maintenance. In my case this engine had never suffered any damage with the exception of exhaust valve failure that did not require an inflight shutdown and did not puncture the piston or generate metal debris in the engine. A new cylinder was installed and all parameters were normal. The oil pressure (60psi at normal operating temps) was the same as it had been when the engine was originally installed. There was absolutely NO indication this engine was in trouble before it failed. The other engine is already being scheduled for overhaul and whatever engine I put on this aircraft to ferry home will be overhauled before regular flying resumes.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.