BE20 CREW FLEW INTO A TSTM CELL IN ZLC CLASS A AIRSPACE.

Narrative

AFTER SMOOTHLY XING AN AREA OF CELLS; WE RETURNED TO COURSE AND SECURED THE AREA AHEAD ON VARIOUS RADAR RANGES; SINCE WE WERE STILL IN CLOUDS. NOTHING PAINTED. ABOUT 10 MINS AFTER PASSING THE LAST CELL; WE HIT A SMALL DIAMETER; VIOLENT; ICE-LADEN CELL. IT DID NOT SHOW ON RADAR. BEFORE I COULD GRASP PWR LEVERS AND REDUCE PWR WE WERE THROWN DOWN VIOLENTLY AND THEN UP VIOLENTLY. WE WERE ABOUT 800 FT HIGH AND IN LIGHT TURB WITHIN 15 SECONDS. WE ADVISED ATC AND RETURNED TO ALT. THE COPLT IMMEDIATELY WENT AFT TO ASSIST PAX; WHO WERE ALL RESTRAINED BY SEAT BELTS. THEIR DOG; HOWEVER; WAS KILLED BY VIOLENT ROOF/FLOOR IMPACT. THE TINY DOG WAS FINE; BUT THE BIGGER DOG (35 LBS) BROKE ITS SPINE. COPLT ALSO INSPECTED WINGS FOR LARGE-SCALE DAMAGE. I DID THE SAME FROM COCKPIT. NO APPARENT WRINKLES. WE OPTED TO FINISH FLT AT MINIMUM MANEUVERING SPD AND DO DETAILED INSPECTION ON GND. GND INSPECTION REVEALED SUBTLE WRINKLES IN SEVERAL PLACES ON BOTH WINGS AND BOTH NACELLES. MANY RIVETS ALSO LOST PAINT. PLANE GNDED FOR FURTHER INSPECTION/REPAIR. LESSONS: 1) NOT ALL SEVERE CUMILIFORM WX CAN BE DETECTED BY RADAR. 2) YOU ARE NOT OUT OF THE WX UNTIL YOU ARE VISUALLY OUT OF THE WX. 3) IF YOU SUSPECT DAMAGE; LAND ASAP. YOU CANNOT SEE DETAIL FROM CABIN/COCKPIT WINDOWS. 4) ANIMALS SHOULD BE RESTRAINED OR KENNELED; UNLESS OWNER IS WILLING TO LOSE THEM.