AN ATR72 WAS DISPATCHED IN NON COMPLIANCE WITH THE FUEL CAP NOT SECURED AND THE FUELING DOOR OPEN.

Narrative

NORMAL TKOF FROM ZZZ. IMMEDIATELY AFTER GEAR RETRACTION; THE FLT ATTENDANT CALLED THE FLT DECK. HE STATED HE HEARD A 'BANGING' FROM THE ACFT; BUT IT HAD STOPPED. ON THIS ACFT; A BANGING IMMEDIATELY AFTER TKOF IS ALMOST ALWAYS CAUSED BY AN UNSECURED FUEL CAP. THE BANGING USUALLY CONTINUES UNTIL THE FLT COMPLETES; OR THE FUEL CAP BREAKS AWAY FROM THE ACFT. SINCE THE BANGING STOPPED; I ELECTED TO CONTINUE TO OUR DEST. UPON SELECTING THE GEAR DOWN FOR LNDG; THE FLT ATTENDANT CALLED AND SAID THE BANGING HAD RESUMED. UPON ARR AT THE GATE; WE OBSERVED THE FUEL DOOR OPEN; WITH THE FUEL CAP STILL ATTACHED. THIS FUEL CAP HAD AN UNUSUALLY SHORT CHAIN. I SURMISE THAT WITH AN UNUSUALLY SHORT CHAIN; COUPLED WITH A CHANGE IN AIRFLOW WITH THE GEAR DOWN; CAUSED THE CAP TO 'STREAMLINE' AND NOT BANG AGAINST THE ACFT. A MECH CHKED OUT THE ACFT AND NOTED 'NO DAMAGE.' THE CAUSE OF THE FUEL CAP LEFT OFF WAS THE FUELER NOT PUTTING THE CAP BACK ON AFTER HE COMPLETED FUELING. A SECONDARY CAUSE WAS THE SHORT TURN TIME AT THE OUTSTATION. BY THE TIME THE FUELER HAD COMPLETED FUELING; THE PAX WERE ON BOARD AND THE PREFLT INSPECTION COMPLETED. THE DESIGN OF THE ATR-72 MAKES A PREFLT INSPECTION VERY DIFFICULT WITH PAX ON BOARD.