MD88 FLT CREW INADVERTENTLY MISDIAGNOSES FIRE LOOP WARNING; SHUTS DOWN ASSOCIATED ENG AND DIVERTS TO THE NEAREST SUITABLE ARPT.

Narrative

APPROX 25 MINS AFTER TKOF AT CRUISE ALT OF FL330; THE 'MASTER CAUTION' LIGHT; THE 'FIRE DETECTOR LOOP' LIGHT ON THE ELECTRICAL OVERHEAD ANNUNCIATION PANEL; AND THE 'L ENG LOOPS' 'LOOP A' LIGHT ON THE 'ENG FIRE DETECTOR SYS' PANEL ILLUMINATED. THE 'FIRE DETECTOR LOOP LIGHT WITH NO FIRE WARNING' CHKLIST WAS RUN TO ITS CONCLUSION WHICH LED TO THE 'ENG FIRE/SEVERE DAMAGE' CHKLIST INCLUDING L ENG SHUTDOWN AND THE DISCHARGE OF BOTH FIRE BOTTLES. AN EMER WAS DECLARED AND ZZZ WAS DETERMINED TO BE THE NEAREST SUITABLE ARPT. FLT ATTENDANTS AND PAX WERE BRIEFED ON WHAT TO POSSIBLY EXPECT. WE RECEIVED TEXTBOOK RESPONSE FROM THE FLT ATTENDANTS; ATC; AND THE ARPT FIRE DEPT. WX AT THE ARPT WAS VFR UNDER AN OVCST SKY. AFTER STOPPING ON RWY; THE FIRE DEPT DETERMINED THAT THERE WAS NO INDICATION OF FIRE; AND WE TAXIED TO THE RAMP. WE COORD WITH OPS PERSONNEL AND TSA OFFICIALS AND THEN THE PAX WERE DISEMBARKED. I AM SURE THAT I AND MY FO RAN THE CHKLIST CORRECTLY. HOWEVER; NOT BASED ON MY MEMORY BUT ON THE PRELIMINARY AND LIMITED INFO THAT WAS AVAILABLE TO ME PRIOR TO MAINT ON THE ACFT; I HAVE CONCERNS THAT IT APPEARS THAT I MAY HAVE INADVERTENTLY SELECTED THE WRONG LOOP AND SELF-INDUCED PART OF THE SITUATION.