A DC20 FALCON FREIGHTER ENTERS A TSTM AT FL310 AND EXPERIENCES SEVERE TURB. FO SAID THAT THE ACFT'S RADAR SHOWED 'A SMALL AREA OF LOWEST INTENSITY.'

Narrative

ATC ADVISED PRECIP AT 12 O'CLOCK POS; IN 10 MI. OUR RADAR SHOWED A SMALL AREA OF LOWEST INTENSITY RETURN IN THAT AREA WHEN WE LOWERED THE RADAR UNITS SCALE (DISTANCE). WE WERE AT FL310; CLRED TO DSND; AND WERE ON A VECTOR DIRECT TO DEST. THE FLT ENCOUNTERED AN APPROX MEDIUM TO SEVERE LEVEL OF INTENSITY OF TURB AND MODERATE TO HVY PRECIP FOR APPROX 30 SECONDS TO 1 MIN. THE CTLR DID NOT OFFER AN INTENSITY BUT MERELY STATED PRECIP AND OUR RADAR SHOWED LOWEST LEVEL OF INTENSITY OF RETURN. WHEN IN THE CLR ON THE OTHER SIDE OF THE NARROW CELL; WE LOOKED BACK TO SEE A TWRING ANVIL ABOVE US. THE ACFT SUFFERED HAIL DAMAGE AND WAS GNDED FOR REPAIR; BEFORE FURTHER FLT; UPON LNDG. THE RADAR DID NOT ACCURATELY DEPICT THE INTENSITY OF THE WX AND THE IMC CONDITIONS OBSCURED OUR VISION (ABILITY TO SEE THE TSTM). WX RPTS; FORECASTS AND PIREPS HAD (PRINTED OUT) INDICATED NO SIGNIFICANT WX AND TURB (NEG) IN THAT AREA. THE RADAR UNIT IN THIS PARTICULAR PLANE HAS A HISTORY OF WRITE-UP'S THAT WE WERE NOT AWARE OF. ATC SHOULD ADVISE OF INTENSITY. MAINT SHOULD CALIBRATE OR REPLACE THE RADAR UNIT.