What was found
ON TAXI OUT RECEIVED LVL 1, FIRE DET 2 FAIL. AFTER STOPPING ACFT, RAN A FIRE TEST & THEN RECEIVED LVL 3, ENG 2 FIRE, ALERT. RAN QRH PROCEDURES, FOR ENG FIRE SEVERE DAMAGE CHECKLIST. FIRED FIRST BOTTLE & ALERT REMAINED ON, AFTER 30 SEC STILL HAD FIRE ALERT ON. FIRED SECOND BOTTLE AFTER ABOUT 2 MINUTES ALERT WENT OUT, BOTH FIRE DET 2 FAIL & ENG 2 FIRE RETURN TO GATE. R & R NR 2 FDCU IAW AMM 26-11-02-4, FDCU CHECKED GOOD IAW AMM 26-11-02-5. R & R NR 2 LT & RT FIREX BOTTLE IAW MM 26-21-01-4. NO EVIDENCE OF FIRE, OK TO CONTINUE. INSTALLED 4 EA NEW FIREX DISCHARGE CARTRIDGES IAW AMM 26-21-05. RAN ENG JRH, OPERATIONS CHECKED GOOD NO FIRE WARN INDICATION. OK FOR SERVICE