E120 CREW WAS SCHEDULED BEYOND MAX ALLOWABLE DUTY TIME.

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CHAIN OF EVENTS: OUR DUTY PERIOD BEGAN AT XA05 AND WAS SCHEDULED TO FINISH AT XK55 FOR A TOTAL OF 11 HRS 50 MINS OF SCHEDULED DUTY TIME. DUE TO MAINT DELAYS; A DIVERSION TO AVOID SEVERE WX AND HEADWINDS; WE WERE BEHIND SCHEDULE. OUR LAST 2 LEGS WERE MEI-LFT AND LFT-DFW. THE DISPATCHER GAVE US A 2-LEG FLT RELEASE. ENRTE TO LFT; I CALCULATED WE MUST TAKE OFF FROM LFT BY XN44 BASED ON THE ENRTE FLT TIME OF 1 HR 21 MINS IN ORDER FOR US TO ARRIVE AT DFW BEFORE 16 HRS WAS EXCEEDED. THE FLT ARRIVED AT THE DFW GATE AT XP05 -- EXACTLY AT 16 HRS OF DUTY TIME; HOWEVER; OUR DUTY TIME DID NOT END UNTIL XP20. THIS RESULTED IN A 16 HR 15 MIN DUTY PERIOD FOR THE DAY. IN REVIEW; I SEE 2 MISTAKES MADE. FIRST; I USED THE ENRTE FLT TIME ON THE FLT RELEASE INSTEAD OF THE SCHEDULED FLT TIME (1 HR 21 MINS ON THE RELEASE VERSUS 1 HR 50 MINS ON THE SCHEDULE). HENCE; TAXI TIME WAS NOT ACCOUNTED FOR. THE SECOND ERROR WAS NOT INCLUDING THE 15 MINS OF DUTY TIME DELETED ONCE A FLT IS BLOCKED IN. THE LATEST WE SHOULD HAVE DEPARTED THE GATE AT LFT WAS XN00. HUMAN PERFORMANCE CONSIDERATIONS: A FACTOR THAT MIGHT HAVE CONTRIBUTED TO THE ERROR IS FATIGUE DUE TO THE PREVIOUSLY MENTIONED DELAYS; FLYING CONDITIONS; AND 8 HRS 50 MINS OF FLYING COMPLETED PRIOR TO THE FINAL LEG (10 HRS 5 MINS TOTAL ONCE THE LAST LEG WAS COMPLETE).