What was found
SCHEDULED MX, BOTH ENG`S STARTED FOR A ROUTINE OPS CHK. ABOUT 4 MINS INTO RUN-UP, WITH PROP BLADES LT IN FLAT PITCH, NR 2 ENG FIRE WARN LIGHT ILLUMINATED. PILOT PERFORMED A CAUTIONARY SHUTDOWN OF BOTH ENG`S. AN INITIAL INSPECT OF NR 2 ENG FOR CAUSE OF FIRE WARN LIGHT ILLUMINATION RESULTED IN NO NOTED DEFECTS. ALL FOUR SENSORS REPLACED & FIRE SENSOR SYS THOROUGHLY INSPECTED. NR 2 ENG ONCE AGAIN STARTED RESULTING IN ANOTHER FIRE WARN ILLUMINATION WITHIN A 5 MIN PERIOD. WITH THIS RUN-UP, NOTED WHEN PROP TAKEN OFF FLAT PITCH LOCKS, WARN LIGHT EXTINGUISHED. FURTHER INVEST, EXHAUST STACK SLIP JOINT REVEALED THAT 2 OF STACK ATTACH RESTRAINTS BROKEN, ALLOWING EXCESSIVE MOVEMENT AT JOINT.