AN MD SUPER 80 BEING TOWED FROM THE GATE TO THE TXWY WITH THE APU INOP AND THE L ENG RUNNING MAKES A XBLEED START OF #2 ENG. JUST AFTER REDUCING PWR ON #1 ENG THE TUG STOPPED INCURRING DAMAGE TO THE TOW BAR.

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APU WAS INOP. STARTED L ENG AT GATE. ZZZ PROCS CALL FOR XBLEED START IN ALLEY. WE PUSHED BACK FROM AZ. AS WE WERE TOWED FORWARD; THE GND MAN ADVISED CLRED TO START ENG #2. SINCE I HAVE DONE VERY FEW XBLEED STARTS; I HAD REVIEWED THE PROC EARLIER AT THE GATE; BUT I HAD NEVER CONSIDERED DOING IT WHILE BEING TOWED. I THOUGHT SINCE THE RAMP ALLEY LOOKED BARE AND DRY AND AS LONG AS I GUARDED THE BRAKES IT WOULD BE SAFE. I WAS WRONG. I DID NOT NOTICE SOME GLYCOL AT SPOT Y. JUST AFTER I REDUCED THE L ENG TO IDLE; THE GND MAN CALLED BRAKES. I IMMEDIATELY STOPPED THE ACFT. THE TUG JACKKNIFED AND THE TOW BAR BENT. I CALLED OUT MAINT TO INSPECT THE NOSE GEAR. THERE WAS NO DAMAGE TO THE ACFT. AFTERWARDS; I ASKED THE TUG DRIVER IF IT WAS NORMAL TO XBLEED START DURING THE TOW AND HE SAID YES. I THINK THAT I WAS WRONG TO USE MORE THAN IDLE PWR WHILE BEING TOWED AND I WILL NEVER DO IT AGAIN. I WILL WAIT UNTIL THE TUG IS DISCONNECTED BEFORE DOING A XBLEED START AND BE MORE CAUTIOUS FOR GLYCOL OR ANYTHING THAT MIGHT PRECLUDE EVEN DOING A NORMAL ENG START DURING TOW. I THINK THAT THERE SHOULD BE MORE GUIDANCE IN THE ACFT FLT MANUAL REGARDING XBLEED STARTS. I AM REALLY CONCERNED ABOUT WHAT COULD HAVE HAPPENED TO THE TUG DRIVER HAD I NOT STOPPED AS QUICK AS I DID.