Narrative:

My four passengers and I were about 60 miles south of our destination at 7;000 ft when I noticed that the manifold pressure on the left engine was an inch or so higher than where I set it. I tried minimal adjustment and got no response. I left it alone for a moment thinking through what the impact of a broken cable might mean. I tried the control again with full deflections both ways with no response. I concluded that the throttle cable was broken or loose. I tried to reduce the mixture; resulting in some change in RPM but was accompanied by a major increase in egt; so I returned it to the normal position. I then tried reducing the prop RPM with some speed decrease but neither option made enough of a power difference to warrant damaging an engine.I concluded that I had to gradually reduce speed and would continue the 50 miles or so to my destination and then cut the left engine when on final. I asked approach to see if they could find a mechanic (a&P) to see if there were any other options and was informed they were working on it. They later came back and said that a CFI in the facility recommend I land immediately.I was unsure whether the throttle would stay at the setting it was at or if it would change through vibration to a lower setting or a higher setting. Before this realization I was content that I had two operating engines and really didn't have an immediate problem. I decided I would rather try to descend circling a field nearby and concluded that I needed to declare an emergency to get the help I needed. I have read many articles about pilots not declaring an emergency and not getting the full benefits available by ATC.I informed center that I was declaring and emergency and would like to attempt a descent to land. I was quickly given vectors and ILS information. I knew I was going to have to cut an engine and did not want to do this IFR if a VFR alternative was available. I was informed ZZZ was VFR but had a ceiling whose altitude I don't recall. I was vectored into solid IFR conditions assured the field would come into sight. At first the controller didn't realize my situation as I was given directions to descend to 4;000 ft from 7;000. I explained that I could only descend if I cut an engine and I wasn't doing that in IMC.the controller said he now understood my situation and reassured me the field would come into view. I was IMC and started a descent under cruise power. This increased airspeed but did offer a decrease in altitude. I kept the airspeed just below the red arc (vne) until reaching 4;000 ft at which time I saw the runway and was turned to a right base. Once on final I knew I could make the runway and pulled the mixture on the left engine and feathered the prop. I pulled the throttle on the right engine and continued reducing altitude before slowing down enough to drop the gear and eventually the flaps and make a normal landing.I removed the cowling and found the broken cable. A local a&P crimped the end back on and after checking the conditions over the rest of the route we departed for our destination for replacement of the cable.

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Original NASA ASRS Text

Title: A BE-55 Pilot experienced a broken throttle cable and loss of control on the left engine while on an IFR flight in mixed conditions. Using some innovative piloting techniques and assistance from ATC he managed to keep the engine running until entering VMC conditions where he shut down the engine and landed.

Narrative: My four passengers and I were about 60 miles south of our destination at 7;000 FT when I noticed that the manifold pressure on the left engine was an inch or so higher than where I set it. I tried minimal adjustment and got no response. I left it alone for a moment thinking through what the impact of a broken cable might mean. I tried the control again with full deflections both ways with no response. I concluded that the throttle cable was broken or loose. I tried to reduce the mixture; resulting in some change in RPM but was accompanied by a major increase in EGT; so I returned it to the normal position. I then tried reducing the prop RPM with some speed decrease but neither option made enough of a power difference to warrant damaging an engine.I concluded that I had to gradually reduce speed and would continue the 50 miles or so to my destination and then cut the left engine when on final. I asked Approach to see if they could find a mechanic (A&P) to see if there were any other options and was informed they were working on it. They later came back and said that a CFI in the facility recommend I land immediately.I was unsure whether the throttle would stay at the setting it was at or if it would change through vibration to a lower setting or a higher setting. Before this realization I was content that I had two operating engines and really didn't have an immediate problem. I decided I would rather try to descend circling a field nearby and concluded that I needed to declare an emergency to get the help I needed. I have read many articles about pilots not declaring an emergency and not getting the full benefits available by ATC.I informed Center that I was declaring and emergency and would like to attempt a descent to land. I was quickly given vectors and ILS information. I knew I was going to have to cut an engine and did not want to do this IFR if a VFR alternative was available. I was informed ZZZ was VFR but had a ceiling whose altitude I don't recall. I was vectored into solid IFR conditions assured the field would come into sight. At first the Controller didn't realize my situation as I was given directions to descend to 4;000 FT from 7;000. I explained that I could only descend if I cut an engine and I wasn't doing that in IMC.The Controller said he now understood my situation and reassured me the field would come into view. I was IMC and started a descent under cruise power. This increased airspeed but did offer a decrease in altitude. I kept the airspeed just below the red arc (Vne) until reaching 4;000 FT at which time I saw the runway and was turned to a right base. Once on final I knew I could make the runway and pulled the mixture on the left engine and feathered the prop. I pulled the throttle on the right engine and continued reducing altitude before slowing down enough to drop the gear and eventually the flaps and make a normal landing.I removed the cowling and found the broken cable. A local A&P crimped the end back on and after checking the conditions over the rest of the route we departed for our destination for replacement of the cable.

Data retrieved from NASA's ASRS site as of April 2012 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.