THE PILOT IN COMMAND REPORTED THAT WHILE IN A CLIMBING RIGHT TURN AT 400 FEET MSL HE ENCOUNTERED A SEVERE DOWNDRAFT WHICH HE COULD NOT ARREST DESPITE THE APPLICATION OF FULL POWER. A COMMERCIAL PILOT WHO DEPARTED ALONG THE SAME ROUTE AS THE ACCIDENT FLIGHT 15 MINUTES AFTER THE OCCURRENCE REPORTED THAT THE AIR WAS STABLE AND THAT NO DOWNDRAFTS WERE ENCOUNTERED. ON THE DAY OF THE ACCIDENT, THE FLIGHT SERVICE STATION (FSS) IN KETCHIKAN DID NOT RECEIVE ANY PILOT REPORTS OF SEVERE DOWNDRAFTS IN THE KETCHIKAN BAY AREA.