PLT OF ATX LTT ACFT LOST CTL OF THE ACFT IN AND AROUND A TSTM WX SYS AND DEVIATED FROM ASSIGNED ALT.

Narrative

AT APPROX PM35Z 30 NE OF PUB AT FL190 WHILE DEVIATING 15 E OF A TSTM; WITHOUT WARNING AND NO INDICATION OF PRECIPITATION OF TURB ON WX RADAR AND THE STORM SCOPE; I INSTANTLY ENCOUNTERED SEVERE RIME ICE; A MOMENTARY UPDRAFT; THEN A DOWNDRAFT WHICH PEGGED THE IVSI AT 6000 FPM DSCNT. WHILE THIS EVENT WAS HAPPENING; I LOST PWR TO BOTH ENGS TO A MAX OF 15 INCHES MP WITH PWR LEVERS FULL FORWARD. I WAS INCREASING PITCH TOWARDS BLUE LINE TO MINIMIZE MY RATE OF DSCNT WHEN THE ACFT BEGAN TO BUFFET (STALL) AT APPROX 120-130 KIAS. I DECREASED PITCH TO MAINTAIN 140 KIAS AND WAS CONTINUING A DSCNT OF 6000 FPM PLUS I SUSPECTED INDUCTION ICING FOR THE DECREASE IN PWR BUT WAS UNABLE TO DO ANYTHING AT THIS TIME. I INFORMED CTR THAT I WAS UNABLE TO MAINTAIN ALT AND ENCOUNTERED SEVERE ICE; AND LOST PWR TO BOTH ENGS. CTR ASKED IF I WANTED TO DECLARE AN EMER AND I SAID AFFIRMATIVE AND REQUESTED DIRECT PUB. AFTER A LOSS OF APPROX 9000 FT THE DOWNDRAFT DIMINISHED; MY WORKLOAD DECREASED TO THE POINT OF DETERMINING THE CAUSE OF THE PWR LOSS. THE R AND L ALTERNATE AIR SOURCE VALVES WERE OPENED AND BOTH ENGS DEVELOPED 100 PERCENT PWR. THIS 3RD AIR SOURCE VERIFIED THAT THE PRIMARY AND SECONDARY AIR SOURCE FOR THE ENGS WERE ICED CLOSED. AFTER OPERATING AT ABOVE FREEZING TEMPS THE R AND L ALTERNATE AIR SOURCE VALVES WERE CLOSED AND THE ENGS CONTINUED TO OPERATE NORMALLY. AFTER CHKING ALL OTHER INSTS AND GAUGES; I DETERMINED THE ACFT WAS OPERATING NORMAL. I CANCELLED THE EMER CONDITION AND PROCEEDED TO OUR ORIGINAL DEST. I WAS A LIFEGUARD FLT AND PATIENT REQUIRED TRANSPORT TO DEST. NO OTHER PROBLEMS ENCOUNTERED WHILE COMPLETING FLT ABOVE FREEZING LEVEL. ZDV'S HELP WAS EXCELLENT WITH MY NEEDS AND REQUESTS TO MAKE THIS POTENTIAL DANGEROUS SITUATION SUCCESSFUL.