ATR42 ON THE GATE WITH PAX ON BOARD; R ENG RUNNING WITH PROP ENG ENGAGED. UNABLE TO RELEASE BRAKE AND STARTED L ENG FOR MAIN SYS HYD PRESSURE. STILL UNABLE TO GET PROP BRAKE RELEASE LIGHT. ADDED TORQUE TO R ENG RESULTING IN OVERHEATING PROP BRAKE SYS AND CAUSING SMOKE AND FIRE. SHUT DOWN ENGS; EVACED ACFT; NO INJURIES; CGP EXTINGUISHED FIRE ON L ENG.

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ATR42 HAS A PROP BRAKE ON THE R-HAND ENG. IT IS A DISC BRAKE ON THE RGB ON THE PW120. IT IS LOCKED BY 3000 PSI OF HYD PRESSURE. THE SYS WILL LOCK/UNLOCK BY A SWITCH IN THE COCKPIT WHEN CERTAIN CONDITIONS ARE MET. WHEN THEY ARE MET; A GREEN READY LIGHT ILLUMINATES IN THE COCKPIT. THE CREW ARE ON THE THIRD DAY OF JFK TO PIT CONTINUOUS DUTY OVERNIGHTS; IE; THE LAST LEG PIT TO JFK. RPT TIME IS XE45 AM. HOWEVER; THE HOTEL TO ARPT RIDE IS 15 MINS AND ANOTHER 10 MINS FROM THE FRONT OF THE TERMINAL TO THE GATE; WAKE UP IS XD45 AM. PREVIOUS NIGHTS HOTEL ARR IS XA00 AM. TOTAL SLEEP TIME IS 3 HRS. SINCE THIS SEQUENCE WAS DONE THE DAY BEFORE; AND ONLY 2 HRS SLEEP DURING THE PREVIOUS DAY; THE CREW WAS CONSCIOUS; BUT FATIGUED; INSIDIOUSLY. THE FATIGUE SHOWS UP IN THE INABILITY TO PROPERLY THINK THROUGH ACTIONS IN THE COCKPIT; EVEN THOUGH I THINK I AM AWAKE ENOUGH. SCENARIO AS FOLLOWS. ACFT AT GATE; LOADED ENG #2 (R-HAND) IS ON AND PROP BRAKE ENGAGED. (ENG IS RUNNING.) I GO TO START AUX HYD PUMP TO GENERATE 3000 PSI; TO UNLOCK PROP BRAKE. HOWEVER; WE GET NO READY LIGHT. CHKLIST SAYS TO START ENG #1 (L HAND). I START ENG #1; MOVE CONDITION LEVEL TO MAX (THIS ACTIVATES NORMAL HYDS). CHK GAUGE. 3000 PSI AVAILABLE. NO READY LIGHT. CHKLIST SAYS SHUT DOWN ENG WITH PROP BRAKE. THIS MEANS THAT THE PROP BRAKE WILL NOT UNLOCK. PROB. SOMEHOW I GET AN IDEA THAT IF I ADD TORQUE FROM THE R HAND ENG; MAYBE THE BRAKE WILL UNLOCK. FLAWED THINKING; AS 3000 PSI IS HOLDING THE PROP LOCKED. HOWEVER THE FATIGUE WAS COMPROMISING AND I DID NOT THINK THIS THROUGH (THE FO WAS NEW ON THE ACFT AND DID NOT QUESTION MY JUDGEMENT). RESULT; THE TORQUE ADDITION HEATED THE PROP BRAKE TO COMBUSTION. WE ENDED UP WITH FLAMES BEHIND THE SPINNER AND IN FRONT OF THE ENG. WE SHUT DOWN BOTH ENGS; DEPLANED THE PAX ORDERLY. THE GND PERSONNEL USED THE FIRE EXTINGUISHER TO PUT OUT THE FLAMES. THE FO WAS SENT WITH THE HALON FIRE EXTINGUISHER FROM THE COCKPIT TO BACKUP. THE ARPT CFR WAS ALERTED AS I CALLED OPS. THE FO AND I WENT BACK TO THE COCKPIT AND FINISHED THE CHKLISTS. ALL COMPANY RPTS WERE MADE. WHY DID I DISREGARD COMMON SENSE AND TRY TO UNLOCK THE PROP BRAKE WHEN I HAVE BEEN CAPT ON THIS ACFT FOR 7 YRS AND 4200 HRS; AND HAVE ALWAYS OPERATED THIS SYS PROPERLY BEFORE. ALSO; WHEN THE FO DID PREEFLT OF THE ACFT; HE TOLD ME THAT HE COULD NOT UNLOCK THE PROP BRAKE. THIS IS SIGNIFICANT. HOWEVER; IT DID NOT REGISTER THAT MORNING! I HAVE NO DOUBT THAT THE CONTINUOUS DUTY OVERNIGHTS; OTHERWISE KNOWN AS 'STANDUP OVERNIGHTS;' IS THE CONTRIBUTING CAUSE TO THIS SIT. HAD I BEEN ON NORMAL DAY OR EVENING TRIPS; I WOULD; AND HAVE BEFORE; THOUGHT IT THROUGH AND SHUT THE ENG DOWN; AND CALLED MAINT ON THE TELEPHONE. THIS IS DIFFERENT THAN NORMAL FATIGUE. YOU GO TO SLEEP LATE AND WHILE YOU GET TO 'DEEP SLEEP;' SUDDENLY YOU AWAKENEN AND ARE EXPECTED TO BE PERFORMING AT A PEAK LEVEL. THIS CANNOT HAPPEN DUE TO THE SLEEP INTERRUPTION. AGAIN; FAILURE TO FOLLOW A SIMPLE CHKLIST; FAILURE TO THINK THROUGH A SIMPLE ACTION IS THE DIRECT RESULT OF INTERRUPTED SLEEP ON MULTIPLE TRIPS; CULMINATING IN INSIDIOUS FATIGUE. ONCE THE FLAMES AROSE; THE ADRENALINE HORMONE RESPONSE KICKED IN; AND THE ENG SHUTDOWN AND PAX DEPLANEMENT OCCURRED QUICKLY AND EFFICIENTLY. THERE WERE NO INJURIES. MY FO AND FLT ATTENDANT PERFORMED TREMENDOUSLY. THE CFR WERE ON THE SCENE WITHIN A MIN OR TWO. TO PREVENT FURTHER OCCURRENCES; MAKE A MINIMUM REST TIME AND DO NOT ALLOW 16 HR DUTY PERIODS THROUGH THE MIDDLE OF THE NIGHT ON A REPEATED; BACK TO BACK BASIS. OF COURSE; IT IS ALL LEGAL. WHAT ABOUT SAFETY. THE WORSE PART ABOUT IT IS THE CREW MEMBER MAY THINK THAT HE/SHE IS AWAKE AND CANNOT DETERMINE THE LEVEL (IE; SAFE/UNSAFE) OF FATIGUE.