Narrative:

I departed gri runway 17. The WX conditions at that time were 300 overcast 3/4 fog, wind 18 at 12, braking action was poor. Takeoff was normal through 1000 ft AGL. I reduced power on the engine to 27 inches manifold pressure for the climb, while making a left turn on course to oma. At this point I encountered moderate rime ice approximately 2500 ft AGL. Manifold pressure on the right engine began to fall off at a rate of 2 inches/1000. My first impression was that ice had blocked the right engine air intake. I applied alternate air and increased the right throttle to compensate for the loss as I continued to climb. After applying full throttle on the right engine I realized that there was a more serious problem. The engine gauges were indicating normal oil temperature, cylinder temperature and oil pressure were ok. Due to the loss of power and the accumulating ice, climb rate was reduced to 600 FPM. The tops were reported at 7500 ft MSL and I broke out at 7600 ft and continued to climb at 500 FPM to 9000 ft. At this point I notified msp that I had a turbo failure and requested the oma WX. It was reporting 3400 overcast 3-5 with no ice reported. I elected to continue to oma based on the fact that I was out of the ice and no exhaust leaks were detected and the fact that the engine continued to run with gauges in the green. Not to mention that had I turned around to gri a downwind approach to low IFR and poor braking with moderate ice was the alternative. The possibility of a go around was nil. I failed to land at the nearest airport but based on the circumstances it was the safest option. Oma was MVFR with an approach into the wind and emergency services. Braking was fair to good. I made a normal landing in oma without incident and did not declare an emergency since it was not necessary to shut the engine down. The problem was caused by the waste gate sticking open causing the exhaust to bypass the turbocharger. It is my understanding that this is a common occurrence with this engine although it was the first time it has happened to me. This problem had the potential for catastrophe had I not been able to climb out of the icing conditions even though the small transport was equipped with full deice equipment. Perhaps a closer examination of the waste gate is in order or more public awareness of this type of problem. Callback conversation with reporter revealed the following information: reporter states that maintenance replaced the whole unit. His concern is that he was unaware of how a turbocharged engine acts when turbo not working. Feels this information would be good for other pilots to know. It acts like a normally aspirated engine and will not develop full power as it climbs. Most pilots, he feels, would be included to shut down the engine needlessly.

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Original NASA ASRS Text

Title: SMT AIR TAXI HAS TURBO MALFUNCTION.

Narrative: I DEPARTED GRI RWY 17. THE WX CONDITIONS AT THAT TIME WERE 300 OVCST 3/4 FOG, WIND 18 AT 12, BRAKING ACTION WAS POOR. TKOF WAS NORMAL THROUGH 1000 FT AGL. I REDUCED PWR ON THE ENG TO 27 INCHES MANIFOLD PRESSURE FOR THE CLB, WHILE MAKING A L TURN ON COURSE TO OMA. AT THIS POINT I ENCOUNTERED MODERATE RIME ICE APPROX 2500 FT AGL. MANIFOLD PRESSURE ON THE R ENG BEGAN TO FALL OFF AT A RATE OF 2 INCHES/1000. MY FIRST IMPRESSION WAS THAT ICE HAD BLOCKED THE R ENG AIR INTAKE. I APPLIED ALTERNATE AIR AND INCREASED THE R THROTTLE TO COMPENSATE FOR THE LOSS AS I CONTINUED TO CLB. AFTER APPLYING FULL THROTTLE ON THE R ENG I REALIZED THAT THERE WAS A MORE SERIOUS PROB. THE ENG GAUGES WERE INDICATING NORMAL OIL TEMP, CYLINDER TEMP AND OIL PRESSURE WERE OK. DUE TO THE LOSS OF PWR AND THE ACCUMULATING ICE, CLB RATE WAS REDUCED TO 600 FPM. THE TOPS WERE RPTED AT 7500 FT MSL AND I BROKE OUT AT 7600 FT AND CONTINUED TO CLB AT 500 FPM TO 9000 FT. AT THIS POINT I NOTIFIED MSP THAT I HAD A TURBO FAILURE AND REQUESTED THE OMA WX. IT WAS RPTING 3400 OVCST 3-5 WITH NO ICE RPTED. I ELECTED TO CONTINUE TO OMA BASED ON THE FACT THAT I WAS OUT OF THE ICE AND NO EXHAUST LEAKS WERE DETECTED AND THE FACT THAT THE ENG CONTINUED TO RUN WITH GAUGES IN THE GREEN. NOT TO MENTION THAT HAD I TURNED AROUND TO GRI A DOWNWIND APCH TO LOW IFR AND POOR BRAKING WITH MODERATE ICE WAS THE ALTERNATIVE. THE POSSIBILITY OF A GAR WAS NIL. I FAILED TO LAND AT THE NEAREST ARPT BUT BASED ON THE CIRCUMSTANCES IT WAS THE SAFEST OPTION. OMA WAS MVFR WITH AN APCH INTO THE WIND AND EMER SVCS. BRAKING WAS FAIR TO GOOD. I MADE A NORMAL LNDG IN OMA WITHOUT INCIDENT AND DID NOT DECLARE AN EMER SINCE IT WAS NOT NECESSARY TO SHUT THE ENG DOWN. THE PROB WAS CAUSED BY THE WASTE GATE STICKING OPEN CAUSING THE EXHAUST TO BYPASS THE TURBOCHARGER. IT IS MY UNDERSTANDING THAT THIS IS A COMMON OCCURRENCE WITH THIS ENG ALTHOUGH IT WAS THE FIRST TIME IT HAS HAPPENED TO ME. THIS PROB HAD THE POTENTIAL FOR CATASTROPHE HAD I NOT BEEN ABLE TO CLB OUT OF THE ICING CONDITIONS EVEN THOUGH THE SMT WAS EQUIPPED WITH FULL DEICE EQUIP. PERHAPS A CLOSER EXAMINATION OF THE WASTE GATE IS IN ORDER OR MORE PUBLIC AWARENESS OF THIS TYPE OF PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT MAINT REPLACED THE WHOLE UNIT. HIS CONCERN IS THAT HE WAS UNAWARE OF HOW A TURBOCHARGED ENG ACTS WHEN TURBO NOT WORKING. FEELS THIS INFO WOULD BE GOOD FOR OTHER PLTS TO KNOW. IT ACTS LIKE A NORMALLY ASPIRATED ENG AND WILL NOT DEVELOP FULL PWR AS IT CLBS. MOST PLTS, HE FEELS, WOULD BE INCLUDED TO SHUT DOWN THE ENG NEEDLESSLY.

Data retrieved from NASA's ASRS site as of July 2007 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.