B737 FLT CREW STARTING ENGINES IS INFORMED BY FLT ATTENDANT THAT PAX BELIEVES ENGINE PANEL IS NOT LATCHED. PAX IS CORRECT.

Narrative

WE WERE LEAVING ZZZ LATE AT NIGHT AFTER A LONG DUTY DAY AND A SHORT LAYOVER. MY FO COMPLETED HER PREFLT TO DEP AND NOTICED THE MECH WAS SVCING THE OIL. THE FLT ATTENDANT TOLD US A PAX WAS CONCERNED ABOUT A RED THING STICKING OUT OF THE COWL OF THE ENG. WE BOTH TOLD HER THE MECH WAS FINISHING SVCING THE OIL (I HAD THE ACARS PRINTOUT STATING THE PAPERWORK WAS INCOMPLETE DUE TO OIL SVC). AFTER WE STARTED BOTH ENGS; SHE CALLED US AGAIN TO SAY THE PAX WAS STILL CONCERNED ABOUT THE 'RED THING STICKING OUT.' I IMMEDIATELY ORDERED MY FO TO SHUT DOWN THE #2 ENG AND TOLD HER TO GO BACK AND LOOK AT WHAT THE PAX WAS SEEING. ALL 3 FLT ATTENDANTS WERE ALL READY TO COVER THE COCKPIT WHILE SHE LOOKED AT THE #2 ENG. THE FO CONFIRMED THAT THE #2 ENG COWL WAS UNLATCHED. WE CALLED LCL MAINT TO GET SOMEONE OUT ASAP. A MECH SHOWED UP ASAP AND CLOSED THE LATCH AND WE HAD A CONFIRMATION THAT THE LATCH WAS CLOSED. AGAIN; I SENT THE FO BACK TO VISUALLY CHK THAT THE LATCH WAS CLOSED. I CALLED MAINT (THROUGH DISPATCH) AND LCL MAINT AND ASKED TO CONFIRM THAT THEY HAD ONLY SVCED THE #2 ENG TO MAKE SURE THE #1 ENG IS OK. THEY CONFIRMED ONLY THE #2 ENG HAD BEEN SVCED. WE CONTINUED THE FLT SAFELY.