LEAR 60 FLT CREW EXPERIENCES 'LOUD BANG' DURING CLB; ACFT CLB PERFORMANCE REDUCED; ICING APPEARS ON WINGS WITH ANTI-ICING SYSTEM SELECTED ON AND 'WING HT' ANNUNCIATOR ILLUMINATED. FLT CREW DSNDS TO LOWER ALT AND CONTINUES TO DEST.

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WHILE CLBING OUT ON AN IFR FLR PLAN; WE EXPERIENCED TWO LOUD BANGS AND A COMPLETE LOSS OF CLB PERFORMANCE. WE HAD NO PAX ONBOARD. THE WX WAS SCATTERED TSTMS FROM DEP TO ABOUT 100 NM INTO OUR RTE E BOUND. WHILE DIVERTING L AND R OF COURSE TO AVOID ECHOES; WE WERE INDICATING ON AIRBORNE WX RADAR AND CLBING THROUGH ROUGHLY FL250; WE HEARD AND FELT A LOUD 'BANG.' WE WERE FLYING IN MODERATE RAIN; IN IMC; WITH AN SAT OF ROUGHLY -10 DEGS CELSIUS. OUR DE-ICE AND ANTI-ICE SYSTEMS WERE ALL ACTIVATED. ABOUT 30 SECONDS LATER; WE HEARD ANOTHER BANG AND OUR 'WING HT' ANNUNCIATOR ILLUMINATED. WE LOOKED AT OUR WING TEMPERATURE GAUGE AND IT READ 'FULL COLD.' AS I WAS THE PF; I LOOKED BACK AT MY PFD AND NOTICED THE AIRPLANE HAD STOPPED CLBING. THE AUTOPLT WAS ENGAGED IN THE 'LVL CHG' MODE TO MAINTAIN 275 KTS IN A CLB. THE ENGS WERE PERFORMING NORMALLY ACCORDING TO THE INSTRUMENTS. WE BOTH THEN ASSUMED WE HAD ACCUMULATED LOTS OF ICE SOMEWHERE; PROBABLY ON THE WINGS. THE CAPT TOOK CTL OF THE ACFT AND DISENGAGED THE AUTOPLT. WE BOTH LOOKED AT OUR RESPECTIVE WINGS FOR ICE; AND WE BOTH ONLY NOTICED A LITTLE BIT OF RIME (NO MORE THAN HALF AN INCH). THE CAPT BEGAN A DSCNT AND CALLED FOR 'WING HT' CHKLIST. I TOLD CTR WE NEEDED TO DSND OUT OF ICING CONDITIONS. AS I COMPLETED THE CHKLIST; WE WERE GIVEN SEVERAL STEP DOWNS UNTIL WE LEVELED OFF AT 7000 FT MSL. THE CHKLIST WAS COMPLETE; AND THE WING ANTI-ICE SEEMED TO BE WORKING. THE CAPT SAID THE ACFT WAS HANDLING NORMALLY. AFTER DISCUSSING THE SITUATION WITH OUR MAINT DEPARTMENT; WE ELECTED TO CONTINUE TO OUR MAINT BASE. NO EMER WAS DECLARED AND WE CONTINUED TO BHM; REMAINING CLR OF VISIBLE MOISTURE EVEN AS WE CLBED BACK TO FL310. THE FLT CONTINUED TO BHM WITHOUT INCIDENT. THE CAUSE IS UNKNOWN AS OF THE DATE OF THIS RPT.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR INDICATED THAT DURING THE CLB; THE ACFT ENCOUNTERED LIGHT RIME ICING ON THE WINDSHIELD AND AIRFRAME. AFTER A FEW MINUTES; A LOUD BANG OCCURRED FOLLOWED BY A LOSS OF ACFT PERFORMANCE IN THE CLB. SEVERAL MORE LOUD BANGS OCCURRED; THE ACFT WAS BEING FLOWN ON THE AUTOPLT WITH 'LVL CHG' SELECTED AND A SPD OF 275 KTS SELECTED. THE EICAS MESSAGE 'WING HT' ILLUMINATED AND THE WING TEMP INDICATED COLD. THE ACFT STOPPED CLBING; AND THE FLT CREW SUSPECTED THE CAUSE TO BE AIRFRAME ICING. FLT CREW NOTIFIED ATC AND BEGAN A DSCNT. UPON REACHING WARMER AIR; THE ICE APPEARED TO DISSIPATE AND ACFT BEGAN TO PERFORM NORMALLY. THE FLT CREW ELECTED TO CONTINUE TO THEIR MAINT BASE TO DETERMINE THE CAUSE OF THE LOUD BANGS. THE ACFT WAS CHKED AND NO DAMAGE TO THE AIRFRAME OR ENGS WERE NOTED. IT WAS SUSPECTED THE ICE WAS DEPARTING THE ACFT AND HITTING THE DELTA FINS CAUSING THE LOUD BANGS TO OCCUR. ADDITIONALLY; IT HAS BEEN NOTED THAT THE THERMAL CTL VALVES FOR THE ANTI-ICE SYSTEM HAVE BEEN KNOWN TO FAIL OCCASIONALLY WHICH MAY HAVE BEEN THE REASON FOR THE 'WING HT' EICAS MESSAGE. RPTR NOTED THAT THERE WAS NO INDICATION OF ICE INGESTION TO THE ENGS.