TAXIING MD80 TAIL PIPE FIRE OBSERVED BY GND CTLR. EMER GND EQUIP CALLED OUT; ACFT STOPPED; PAX EVACED. PERSONAL INJURIES TO 6 PAX.

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DURING NORMAL PUSHBACK AND ENG START OF MD80 ACFT #1 ENG STARTED NORMALLY. #2 ENG START ABORTED PRIOR TO ANY INDICATION OF EGT (LIGHT-OFF) AND WHAT WAS BEGINNING TO APPEAR TO BE AN ABNORMALLY LONG TIME FOR LIGHT-OFF; ALTHOUGH NOT THE FULL 20 SECONDS ALLOWED. THE FLT HAD BEEN CLRED TO TAXI AND FOLLOW TFC; NECESSITATING AN IMMEDIATE TAXI; WHICH WAS DONE ON #1 ENG WHILE WE ALLOWED #2 ENG TO SPOOL DOWN. ONCE ON THE TXWY AND HOLDING FOR TFC AN ENG CLRING PROC WAS PERFORMED. SHORTLY THEREAFTER TWR ADVISED THAT THE TAILCONE AREA OF THE ACFT WAS AFLAME. ALTHOUGH WE SUSPECTED POSSIBLE HVY WHITE SMOKE FROM THE CLRING PROC; TWR ADVISED THAT THERE WERE FLAMES VISIBLE FROM THE TAILCONE (APU LOCATION). ACFT SECURED AND AN EMER EVAC PERFORMED. BOTH THE ABORTED START AND THE CLRING PROC WERE PERFORMED WITH A 7-10 KT TAILWIND; DIRECTLY UP THE EXHAUST. I SUSPECT THAT IT IS POSSIBLE THAT THE KEROSENE CLOUD GENERATED BY CLRING THE ENG WITH A TAILWIND WAS DRAWN INTO THE APU INTAKE; CAUSING TORCHING OF THE EXHAUST LOCATED NEXT TO #2 ENG (AND POSSIBLE IGNITION OF THE KEROSENE CLOUD GENERATED DURING CLRING). HAD WE HAD DIRECT COM WITH THE FIRE EQUIP; IT IS POSSIBLE THAT AN EVAC WOULD NOT HAVE BEEN REQUIRED. AN EVALUATION OF ENG CLRING PROCS WITH A TAILWIND SHOULD BE PERFORMED TO DETERMINE TORCHING SUSCEPTIBILITY OF THE APU AND POSSIBLE FUEL CLOUD IGNITION. THE INTAKE AND EXHAUST (APU) APPEAR TO BE PRONE TO TORCHING IN THIS SIT DUE TO THEIR LOCATION. SUPPLEMENTAL INFO FROM ACN 346257: AFTER STARTING THE MOTORING (NO INTENT TO START) WE HEARD ON GND CTL; SOMETHING TO THE EFFECT; 'ACR MD80; YOU HAVE SMOKE OR FLAMES IN YOUR TAIL AREA.' I DISTINCTLY REMEMBER SCANNING ALL OUR INSTS AND ANNUNCIATOR LIGHTS FOR ANY ABNORMAL INDICATIONS OR ILLUMINATION -- THERE WAS NOTHING ABNORMAL! GND CTL NEXT SAID SOMETHING TO THE EFFECT; 'ACR ACFT APCHING TXWY J YOU HAVE 'FLAMES' COMING FROM YOUR TAILCONE.' THAT CONFIRMED IT WAS US. THE CAPT THEN DIRECTLY ASKED GND CTL TO VERIFY THEY SAW 'FLAMES.' GND RESPONDED THAT THEY SAW 'FLAMES FROM THE TAILCONE.' THE CAPT THEN VERIFIED THAT EMER VEHICLES WERE 'ROLLING.' GND CONFIRMED THIS. HE SET THE BRAKE; TOLD ME TO START THE EMER EVAC CHKLIST; WHICH I DID. HE NOTIFIED THE FLT ATTENDANTS AND THE EMER EVAC WAS ON. 6 PEOPLE INJURED. #2 ENG AND TAILCONE AREA HEAVILY FOAMED. UPON VISUAL INSPECTION ONCE OUTSIDE SHOWED NO SIGN OF FIRE IN #2 ENG OR THE APU.