EXTERNAL PWR UNIT CONNECTED TO ACFT CATCHES FIRE.

Narrative

THE ENGS WERE BEING STARTED USING A GND PNEUMATIC STARTING UNIT DUE TO AN INOP APU -- L ENG START WENT NORMALLY; BUT DIDN'T GET MUCH ROTATION ON R ENG. WHILE CHKING THE COCKPIT FOR THE REASON; THE PUSHBACK TUG DRIVER SAID SOMETHING ABOUT A PROB WITH THE START UNIT AND THEN JUMPED OFF THE TUG AND RAN TOWARD THE TAIL OF THE ACFT (LOCATION OF THE START UNIT AND HOSE THAT CONNECTS IT TO THE ACFT) AND OUT OF SIGHT. ABOUT THIS TIME A FLT ATTENDANT CALLED ON THE INTERPHONE AND SAID THERE WAS A FIRE ON THE L SIDE OF THE ACFT. WE HAD NO INDICATIONS OF ANY PROBS WITH THE ENG THAT WAS RUNNING SO WE CALLED THE RAMP TWR AND DISCOVERED THE FIRE WAS IN THE START UNIT; AND THAT THE FIRE TRUCKS HAD BEEN CALLED. IT SEEMS THAT 1 OF THE GND PERSONNEL HAD NOT ONLY DISCONNECTED THE UNIT BUT ALSO HAD JUMPED ON THE SMALL TUG IT WAS CONNECTED TO AND PULLED THE FLAMING UNIT AWAY FROM OUR AIRPLANE AND ITS 138 PAX; 3 FLT ATTENDANTS AND 2 PLTS. WHEN OUR TUG DRIVER RETURNED AFTER 2 OR 3 MIN WE WERE PUSHED FURTHER AWAY FROM THE BURNING START UNIT. ONLY THEN COULD WE FINALLY SEE IT AND THE 10-15 FT HIGH FLAMES THAT COMPLETELY ENVELOPED IT. APPROX 5 MIN AFTER IT STARTED; THE FIRE HAD WATER PUT ON IT BY A FIRE TRUCK: IT WAS STILL BEING FOUGHT AS WE TAXIED AWAY. 2 LESSONS COULD BE LEARNED: 1) OUR TUG DRIVER WAS OUR ONLY SOURCE OF INFO WITH ACCESS TO THE BIG PICTURE AND HE LEFT. WE WERE LEFT WITH PRECIOUS LITTLE INFO UPON WHICH TO BASE DECISIONS THAT COULD HAVE BEEN CRITICAL TO OUR PAX AND CREW. FROM OUR POINT OF VIEW; HE SHOULD HAVE STAYED WITH US AND LET OTHERS HANDLE THE CART. 2) THE GND CREW WAS STILL WRESTLING WITH THE PORTABLE FIRE BOTTLE'S HOSE WHEN THE FIRE TRUCK ARRIVED. THEY WERE UNABLE TO APPLY ANY WATER/AGENT TO THE FIRE. IT APPEARED TO BE A PROB OF TANGLED HOSE. SUCH EQUIP MUST BE MAINTAINED IN A READY STATE AND DRILLS SHOULD BE CONDUCTED. IT DOESN'T TAKE MUCH IMAGINATION TO UNDERSTAND HOW SUCH A DELAY COULD COST LIVES.