PA-23 SUFFERS INDUCTION ICING AND A SUBSEQUENT FAILURE OF THE AUTOMATIC ALTERNATE AIR FUNCTION AND LOSES ENG PWR.

Narrative

BEGINNING DSCNT FROM 9000 FT MSL VMC TO 5000 FT MSL IMC IN SNOW SHOWERS. LOST L THROTTLE CTL OF ENG. ENG WAS DEVELOPING INTERMEDIATE PWR BUT WOULD NOT ACCELERATE OR DECELERATE; ACFT WAS 1974 PA-23 AZTEC (TURBO). R ENG OK. CONTINUED DSCNT TO 3100 FT MSL (MEA) TOWARD GARDNER VOR. UPON REACHING 3100 FT MSL ENCOUNTERED MARGINAL VFR CONDITIONS AND CONTINUED DSCNT TO 2800 FT MSL AND TURNED NW TOWARD DEST ARPT (0B5) TURNERS FALLS; WHILE REQUESTING VECTOR FROM ZBW FOR NEAREST ARPT. RECEIVED VECTOR FOR ORANGE ARPT (ORE) 3 MI N OF POS FROM ZBW. TURNING BASE AT ORANGE IN VMC CONDITIONS; RECOVERED CTL OF L ENG PWR (NORMAL CTL). LANDED WITHOUT FURTHER INCIDENT. AFTER LNDG; AND MECH INSPECTED ACFT AND ENGS AND FUEL SYS WITHOUT FINDING CAUSE FOR THROTTLE CTL LOSS; RETURNED TO HOME ARPT N VMC WITH NO FURTHER PROBS. SUSPECT INDUCTION ICING IN L ENG DURING MC FLT AND AUTOMATIC ALTERNATE AIR FEATURE FAILURE WHICH IS VERY INCIPIENT CAUSING PLT TO USE MANUAL ALTERNATE AIR TO KEEP ENGS RUNNING PROPERLY. RECOMMENDATION: OPEN MANUAL ALTERNATE AIR CTLS ON PA-23 ALWAYS PRIOR TO ENTERING KNOWN OR SUSPECTED ICING CONDITIONS.