ACR HAS PWR LOSS ON GND. START OF APU CAUSES PAX PANIC AND EVAC.

Narrative

WHILE WAITING FOR EXTERNAL PWR TO BE HOOKED UP TO THE ACFT; THE ENG PROVIDING SHIPS PWR WAS SHUTDOWN. AS THE FE I INFORMED THE CAPT THAT WE LOST PWR AND I WAS STARTING THE APU. AS THE APU WAS COMING ON LINE I MADE A PA THAT EVERYTHING WAS FINE AND THE APU WAS BEING STARTED. PEOPLE IN THE R SIDE MAY NOTICE A FLASH OF EXHAUST FIRE. THIS IS NORMAL. UNFORTUNATELY BTWN STARTING THE APU; CHKING SOME SWITCHES AND MAKING THE PA (APPROX 20-25 SECONDS) ALL 4 OVERWING EXITS WERE REMOVED AND THE PAXS STARTED TO EVAC THE ACFT. OUR FIRST INDICATION OF ANY PROBLEM WAS THE LEAD FLT ATTENDANT YELLING FOR EVERYONE NOT TO PANIC AND MAINT PEOPLE COMING UP THE STAIRS ASKING WHAT THE TROUBLE WAS. (APPROX 40-50 PEOPLE WERE ALREADY OUT OF THE ACFT WITHIN 30 SECONDS) ONCE THE PWR WAS RESTORED TO THE ACFT EVERYONE CALMED DOWN QUICKLY. I THINK THE PROBLEM CAUSING THE INCIDENT CAN BE ATTRIBUTED TO 1) POOR JUDGEMENT TO SHUT DOWN THE ENG WITHOUT BEING CLRED; 2) POOR JUDGEMENT AND PANIC ON THE PART OF A FEW PAXS SITTING NEAR THE R WING; 3) THE TORCHY EFFECT OF THE APU LOOKS WORSE AT NIGHT FROM A DARK ACFT. TO CORRECT THIS PROBLEM A PA SHOULD BE MADE ONCE EVERYONE HAS BOARDED EXPLAINING ABOUT THE APU EXHAUST OVER THE R WING AND ANYTIME THE APU IS STARTED NORMALLY A BRIEFING CARD MAY BE MADE FOR THOSE SEATS ON THE R WING. I FEEL A FAILURE OF THE CAPT TO COMMUNICATE HIS INTENTIONS LED TO THE ENG BEING SHUT DOWN PRIOR TO GND PER BEING HOOKED UP. I THINK THE CREW RESPONDED QUICKLY AND PROFESSIONALLY TO THE PAXS. THE PAX NEAR THE R WING MAY HAVE ADDED TO THE SITUATION. HER HYSTERICAL PANIC EFFECTED EVERYONE'S SOUND JUDGEMENT LEADING MANY PEOPLE TO ACTUALLY GO OUT ON A WING THEY THOUGHT WAS ON FIRE. OVERALL I THINK THIS INCIDENT WILL CONTINUE TO HAPPEN IN OUR INDUSTRY UNTIL CHANGES ARE MADE IN THE PA PROC OR THE EXHAUST POS IS CHANGED. THE NEXT 2 DAYS THE SAME SITUATION OCCURRED 3 TIMES ON 4 LEGS. IT IS COMMON (POOR ARPT GND PWR AND FREQ CTL). THOSE TIMES A BRIEF TO THE PAXS PRECEDED THE START OF THE APU. SUPPLEMENTAL INFO FROM ACN 227697. SOME PAX PANICKED SEEING APU TORCH. YELLED FIRE AND PAXS EVACED THROUGH OVERWING EXITS WITH NO AUTHORITY. FLC UNAWARE UNTIL SITUATION WAS OVER. GND CREW PERFORM EXCELLENT BACK UP.