As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6358 - DCA - AIRCRAFT ON GROUND AT GATE, WITH CREW IN COCKPIT. OCCURRED PRIOR TO PUSHBACK. APU DEACTIVATED PER MEL SEQ 49-1, APU FIRE DETECTION DEACTIVATED PER MEL SEQ 26-11. FOUND APU INNER EXHAUST STACK SEPARATED AT TURBINE OUTLET. REPLACED INNER EXHAUST STACK CLAMP. BOTH MEL''S CLEARED. (M)