A REGIONAL JET CL65 ON APCH AT 4000 FT DECLARED AN EMER DUE TO UNABLE TO EXTEND THE TRAILING EDGE FLAPS CAUSED BY THE ASYMMETRICAL FLAP SYS SENSING A SPLIT FLAP CONDITION.

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DURING APCH FOR LNDG AT TLH; I CALLED FOR THE FLAPS TO BE SELECTED TO EIGHT DEGS. I RECEIVED A 'FLAPS FAIL' CAUTION MESSAGE ON THE EICAS. THE FLAPS REMAINED AT 0 DEGS. ATC WAS NOTIFIED OF THE FLAP MALFUNCTION AND NOTIFIED THAT ADDITIONAL TIME WOULD BE NEEDED TO RUN THE APPROPRIATE CHKLIST. WE FOLLOWED THE ABNORMAL PROC CHKLIST IN THE QRH. I NOTIFIED ATC THAT WE WERE DECLARING AN EMER. AT MY DIRECTION; THE FO CONTACTED THE LCL STATION. HE FULLY INFORMED THE LCL STATION OF OUR SIT AND ASKED THE STATION TO CALL COMPANY DISPATCH SO LNDG PERFORMANCE DATA COULD BE COMPUTED. WE FLEW VECTORS AWAITING THE LNDG PERFORMANCE DATA. AT MY INSTRUCTION; THE FO BRIEFED THE FLT ATTENDANT OF THE SIT; AND THEN MADE A PA TO THE PAX. HAVING HEARD NO RESPONSE FROM THE LCL STATION; WE CONTACTED THEM AGAIN FOR THE LNDG DATA FOR WHICH WE HAD REQUESTED THEY OBTAIN FROM COMPANY DISPATCH. AFTER SEVERAL CALLS WITH NO RESPONSE; THEY FINALLY ANSWERED THAT WE HAD TO CONTACT DISPATCH AND MAINT CTL FOR THE DATA. I COMPUTED THE LNDG DATA INFO USING THE FLT STANDARDS MANUAL. BASED ON MY COMPUTATIONS; I CONCLUDED THAT THE PLANE COULD LAND SAFELY. THE FO CONCURRED. DURING FINAL APCH; I CALLED FOR GEAR DOWN. IMMEDIATELY FOLLOWING THE GEAR DOWN; AS I WAS PREPARING FOR THE BEFORE LNDG CHKLIST; THE LCL STATION INTERRUPTED; AND INQUIRED ABOUT THE NATURE OF THE FLAP PROB. THE FO REPLIED THAT HE HAD ALREADY PROVIDED THAT INFO. ADDITIONALLY; THE FO INFORMED THE LCL STATION THAT WE WERE ON APCH AND DID NOT HAVE TIME TO EXPLAIN AGAIN. THE LNDG WAS UNEVENTFUL; EXCEPT WHEN I ATTEMPTED TO DEPLOY THE THRUST REVERSERS THEY DID NOT DEPLOY. THE PLANE CAME TO A STOP WITHOUT ANY PROBS; AND WE CLRED THE RWY. AT THIS TIME WE ARMED THE THRUST REVERSERS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE EXACT PART THAT FAILED WAS NOT KNOWN BUT IT WAS IN THE ASYMMETRICAL FLAP SENSING CIRCUIT EITHER A SENSOR; SWITCH OR TARGET. THE RPTR SAID THE FLAPS ARE ELECTRICALLY OPERATED AND THERE IS NO ALTERNATE METHOD OF FLAP EXTENSION. THE RPTR STATED THE ACR; BECAUSE OF FREQUENT FLAP RPTS OF FAILURE TO EXTEND; HAS CHANGED THE PREFLT CHK PERFORMED BY THE CREW. THE RPTR SAID THE FLAPS ARE NOW EXTENDED FOR THE CHK TO 20 DEGS AND THE GAP BTWN THE INBOARD AND OUTBOARD FLAPS SHOULD BE 4 INCHES -- ANYTHING LESS OR GREATER IS OUT OF LIMITS. THE RPTR ALSO STATED FLAP EXTENSION AIRSPD HAS DECREASED FROM 228 KTS TO 215 KTS.