DO328 JET FLC RETURN LAND AFTER THE RED DOOR WARNING LIGHT CAME ON JUST AFTER TKOF.

Narrative

EVENT: MECHANICAL INTERRUPTION INFLT -- DOOR RED WARNING PANEL LIGHT INFLT RIGHT AFTER DEP; SUBSEQUENT RETURN TO LGA. INITIAL PREFLT CONDUCTED ON ACFT IN LGA. EVERYTHING FOUND TO BE AIRWORTHY -- ALL ACCESS DOORS CHKED; OPENED AND CLOSED AS PART OF ACCEPTANCE CHK. EXTERIOR PREFLT COMPLETED; INTERIOR PREFLT COMPLETED. ALL CHKLISTS COMPLETED NORMALLY; IE; TURN; BEFORE ENG START; AFTER START; TAXI ETC. I WAS THE PF. AFTER ROTATION AND GEAR RETRACTION; THE DOOR RED WARNING PANEL ILLUMINATED WITH A TRIPLE CHIME. WE CONTINUED FLYING THE DEP PROC AND REQUESTED VECTORS BACK TO LGA. (RED WARNING PANEL WENT ON ABOUT 400-500 FT AGL; OF COURSE WELL PAST V1.) AN EMER WAS NOT DECLARED -- WE SIMPLY NEEDED TO RETURN TO THE ARPT. THE DOORS SYS SYNOPTIC PAGE INDICATED THAT THE GND AIR DOOR WAS OPEN; OR THAT THE SWITCH HAD MALFUNCTIONED. WE LANDED UNEVENTFULLY; AND UPON TAXI-IN WERE MET BY THE FAA FOR A RAMP CHK; WHO IMMEDIATELY ASSIGNED BLAME TO THE FLC FOR TAKING OFF WITH THE DOOR OPEN. I STATED THAT THIS WAS NOT TRUE -- I DID A THOROUGH PREFLT; ALL DOORS WERE CLOSED WHEN I GOT ON THE ACFT. NOT ONLY THAT; BUT IT IS NOT POSSIBLE TO TAKE OFF WITH THE GND AIR DOOR OPEN FOR THE FOLLOWING REASON: THE GND AIR DOOR THAT OPENED INFLT HAS A MICROSWITCH THAT SIGNALS OPEN OR CLOSED ON THE DOORS SYS PAGE. PROX SENSOR AND MICROSWITCHED DOORS ARE VERIFIED PRIOR TO PUSHBACK DURING THE BEFORE START CHK BY LOOKING AT THE COCKPIT SYNOPTIC; VERBALLY CALLING OUT THE STATUS OF THE DOORS (RECORDED ON THE CVR) AND FURTHER VERIFIED BY THE ABSENCE OF A DOOR RED WARNING PANEL LIGHT. PRIOR TO THIS; ALL ANNUNCIATOR LIGHTS ARE TESTED VIA A LAMP TEST DURING THE PWR UP PROC. FINALLY; THE RAMP CREW GIVES A 'DOORS CLOSED' HAND SIGNAL (WHICH WE DID RECEIVE) AFTER PUSHBACK; TO VERIFY THAT ALL DOORS ARE CLOSED; INCLUDING THOSE WITHOUT ANY ELECTRONIC INDICATION (SUCH AS THE GPU/HEADSET PANEL). THE GND DOOR WAS WRITTEN UP AFTER LNDG BACK IN LGA. MAINT CTL THEN CLRED THE WRITE-UP; AND WE RE-DEPARTED FOR BNA. THE REST OF OUR DAY AND SUBSEQUENT LEGS WERE UNEVENTFUL. POSSIBLE CONTRIBUTING FACTORS TO EVENT: THIS WAS A SIMPLE OCCURRENCE OF SOMETHING MECHANICAL MALFUNCTIONING. SINCE SEP/11 THE NEW SECURITY PREFLT PROCS REQUIRE ALL ACCESS PANELS ON THE AIRPLANE BE INSPECTED WITH EVERY ACFT ACCEPTANCE CHK. THESE ACCESS PANELS INCLUDE DOORS THAT ARE NOT NORMALLY USED EXCEPT FOR ABNORMAL/UNUSUAL CONDITIONS; SUCH AS GND AC PWR; BATTERY COMPARTMENTS; EXTERNAL AIR; ETC. HOWEVER; THEY ARE NOW CHKED/OPERATED VERY FREQUENTLY. I WONDER IF ALL THE OPENING AND CLOSING OF VARIOUS DOOR/HINGE/LATCH MECHANISMS FLEETWIDE WITH EVERY CREW CHANGE MAKES THESE PANELS/DOORS MORE SUSCEPTIBLE TO FAILURE THAN THEY OTHERWISE WOULD BE -- NOT AT ALL IMPLYING THESE SECURITY CHKS SHOULD NOT BE MADE -- I THINK THEY SHOULD BE CHKED. THIS IS JUST A PERSONAL HYPOTHETICAL OF WHAT MAY HAVE BEEN A CONTRIBUTING FACTOR TO WHY THE DOOR OPENED INFLT.