What was found
FLIGHT 3872, FLAPS FAIL CAUTION MESSAGE, AT 12,000 FT FLAPS WAS NOT EXTENDED, FAILED AT ZERO. NO EMERGENCY WAS DECLARED AND FLIGHT LANDED WITHOUT FURTHER INCIDENT. TROUBLESHOOT PER FIM 27-50-00. COMPLIED WITH PA AD27-052G. REMOVED AND REPLACED RIGHT BPSU IAW AMM 27-51-10. OPS CHECKED GOOD, AIRCRAFT OK FOR SERVICE.