CARJ EXPERIENCES FAILURE OF FLAPS TO EXTEND FOR LNDG.

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AT 2500 FT MSL FO CALLED FOR FLAPS 8 DEGS ON APPROX A 7 MI R BASE FOR RWY. CAPT SELECTED FLAPS 8 DEGS; WHICH WAS FOLLOWED IMMEDIATELY BY A FLAPS FAIL MASTER CAUTION MESSAGE. ADVISED ATC OF THE NEED FOR DELAY VECTORS AND ASSIGNED A CLB TO 3000 FT MSL. FO MAINTAINED PF STATUS; CAPT RAN QRH FOR FLAPS FAIL AND SUBSEQUENT ZERO FLAP LNDG WAS BRIEFED FOR RWY (VISUAL; BACKED UP BY ILS). ATC WAS ADVISED AND THE EMER DECLARED. DISPATCH NOTIFIED VIA ACARS. FLT ATTENDANT BRIEFED ON THE SITUATION AND PLAN; INCLUDING TO NOT BRACE THE CABIN FOR LNDG. PAX UPDATED ON REASON FOR LENGTHY VECTORS AND ABNORMAL LNDG; INCLUDING HIGH APCH SPD AND FIRE TRUCKS ROLLING AS A PRECAUTION. ACFT CTL XFERRED TO CAPT AND APCH FLOWN AT 46000 LBS 174 KT SPD. TOUCHDOWN WAS GENTLE WITH MAX REVERSE AND BRAKING UNTIL STOPPING ASSURED. BRAKES NEVER EXCEEDED 8 ON BTMS (BRAKE TEMP MONITORING SYS). POSSIBLE FAULTY FLAP ELECTRONIC CTL UNIT (FECU)? LOGBOOK INDICATED FLAPS FAILED ON 2 PREVIOUS FLTS IN MAY AS WELL. ON INITIAL FLAP SELECTION HANDLE WAS NOT INADVERTENTLY MOVED PAST POS AND THEN RETURNED TO FLAPS 8 DEGS.