Narrative:

On leveling at FL240; I elected to begin reducing the power with the throttles as soon as I leveled instead of allowing speed to build since I was not on a cross country flight; but just needed to be at FL240 for 2 minutes or less. On leveling; I began to very slowly reduce the manifold pressure from the 35 inch company prescribed climb setting. I was planning to reduce to perhaps 28 or so inches over an approximate 1 minute timeframe so as to allow the engines an easy transition to the lower power setting. As I understand company policy; all climbs are to be made with a full rich mixture and cowl flaps full open to help prolong the life of the engine components which can be otherwise subject to heat stress and premature failure. So this climb was no exception and mixtures remained full rich and cowl flaps open. All engine parameters were actively monitored by me during the entire climb as I normally do and no abnormal indications were noted within a few seconds of having reduced the power by approximately 2 inches to approximately 33 inches; there was a noticeable and sudden yawing of the airplane and substantial difference in engine noise such as quickly out of phase; then quieter. I quickly performed a size-up of engine instruments while simultaneously performing emergency procedures for an engine failure. I noted the #2 engine had nearly no manifold pressure showing; although I don't recall what the actual reading was; it was at or near the bottom of the scale. A glance at the #2 egt confirmed that engine had substantial or total power loss as it was pegged on the bottom of the scale. The #1 engine was operating normally; so I elected to perform engine shutdown as prescribed in the emergency checklist and feathered and shut down at that time. As soon as that was done; I notified center that my #2 engine had failed and was declaring an emergency and wished to return to ZZZ. Center cleared me to proceed to ZZZ and once I stated the nature of the emergency; souls on board; fuel on board; etc; was told to contact approach. Approach cleared us for the visual. We were approximately 14 NM or no north of ZZZ and had the airport in sight and proceeded to runway xx and landed without further incident. I was unaware that there was a recommendation in the pilot operating handbook to lean the mixtures slightly at high altitudes above about FL180 and that power loss or engine roughness could occur if not done. Counting all my PA31-350 experience for the commuters over the past years; I have literally hundreds and hundreds of safe and uneventful climbs as pilot in command to my credit and pride myself on operating the airplanes as if I personally owned them and paid the maintenance bills on them. I strongly believe in adhering to company policies regarding how to operate these engines for maximum lifespan of the components and care immensely about crew and passenger safety. I am fully aware that I am the only pilot in command responsible for the outcome of this flight and regret that I didn't take the pilot operating handbook a bit more seriously. As I write this; I am still unaware as to whether there was any mechanical failure as maintenance is still investigating and has not notified me of any substantial results found in that regard. The director of operations mentioned to me after the flight that it helps to lean the mixtures above 180 to keep the plugs from fouling. I had only done one other high altitude mission in the PA31-350 earlier this year and the weather was very cold; particularly up at altitude it was a -50F. Other than that after-the-fact mention of leaning at very high altitudes; I was never told anything at all about this and was going by the procedure that I knew worked on the literally hundreds of climbs I'd made in the past. As I said though; those climbs; with the exception of the other flight this winter were all made to below 12;000 ft and generally below 10;000 ft for the vast majority due to oxygen requirements

Related reports:

Google
 

Original NASA ASRS Text

Title: Upon leveling at FL240 and reducing power; the right engine of the PA31-350 failed. Pilot declared an emergency and diverted; the failure to lean the mixture during the climb may have contributed.

Narrative: On leveling at FL240; I elected to begin reducing the power with the throttles as soon as I leveled instead of allowing speed to build since I was not on a cross country flight; but just needed to be at FL240 for 2 minutes or less. On leveling; I began to very slowly reduce the manifold pressure from the 35 inch company prescribed climb setting. I was planning to reduce to perhaps 28 or so inches over an approximate 1 minute timeframe so as to allow the engines an easy transition to the lower power setting. As I understand company policy; all climbs are to be made with a full rich mixture and cowl flaps full open to help prolong the life of the engine components which can be otherwise subject to heat stress and premature failure. So this climb was no exception and mixtures remained full rich and cowl flaps open. All engine parameters were actively monitored by me during the entire climb as I normally do and no abnormal indications were noted within a few seconds of having reduced the power by approximately 2 inches to approximately 33 inches; there was a noticeable and sudden yawing of the airplane and substantial difference in engine noise such as quickly out of phase; then quieter. I quickly performed a size-up of engine instruments while simultaneously performing emergency procedures for an engine failure. I noted the #2 engine had nearly no manifold pressure showing; although I don't recall what the actual reading was; it was at or near the bottom of the scale. A glance at the #2 EGT confirmed that engine had substantial or total power loss as it was pegged on the bottom of the scale. The #1 engine was operating normally; so I elected to perform engine shutdown as prescribed in the Emergency checklist and feathered and shut down at that time. As soon as that was done; I notified Center that my #2 engine had failed and was declaring an emergency and wished to return to ZZZ. Center cleared me to proceed to ZZZ and once I stated the nature of the emergency; souls on board; fuel on board; etc; was told to contact Approach. Approach cleared us for the visual. We were approximately 14 NM or no north of ZZZ and had the airport in sight and proceeded to Runway XX and landed without further incident. I was unaware that there was a recommendation in the Pilot Operating Handbook to lean the mixtures slightly at high altitudes above about FL180 and that power loss or engine roughness could occur if not done. Counting all my PA31-350 experience for the commuters over the past years; I have literally hundreds and hundreds of safe and uneventful climbs as Pilot in Command to my credit and pride myself on operating the airplanes as if I personally owned them and paid the maintenance bills on them. I strongly believe in adhering to company policies regarding how to operate these engines for maximum lifespan of the components and care immensely about crew and passenger safety. I am fully aware that I am the only Pilot in Command responsible for the outcome of this flight and regret that I didn't take the Pilot Operating Handbook a bit more seriously. As I write this; I am still unaware as to whether there was any mechanical failure as maintenance is still investigating and has not notified me of any substantial results found in that regard. The Director of Operations mentioned to me after the flight that it helps to lean the mixtures above 180 to keep the plugs from fouling. I had only done one other high altitude mission in the PA31-350 earlier this year and the weather was very cold; particularly up at altitude it was a -50F. Other than that after-the-fact mention of leaning at very high altitudes; I was never told anything at all about this and was going by the procedure that I knew worked on the literally hundreds of climbs I'd made in the past. As I said though; those climbs; with the exception of the other flight this winter were all made to below 12;000 FT and generally below 10;000 FT for the vast majority due to oxygen requirements

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.