What was found
(CAN) ON APPROACH, WHILE LOWING THE FLAPS, THE CREW RECEIVED A FLAP FAIL CAUTION MESSAGE WHEN FLAPS WERE SELECTED FROM 8 TO 20 DEGREES. THE FLAPS STOPPED AT APPROXIMATELY 13-17 DEGREES. THE CREW CONDUCTED A GO AROUND, DECLARED AN EMERGENCY AND THEN LANDED WITHOUT ISSUE. MAINTENANCE DISCOVERED THE R/H FLAP BPSU (BRAKE POSITION SENSOR UNIT) FAULTY. IT HAS BEEN REPLACED AND THE A/C RETURNED TO SERVICE. (TC# 20190618014)