A B737-300 DISCOVERS A MALFUNCTIONING AILERON DURING PRE TKOF CHK AT IAH; TX.

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FLT XX TAXIED OUT. AS WE BEGAN OUR TAXI CHK AND CHKED OUR FLT CTLS; A VERY ASSERTIVE AND OBSERVANT FO NOTICED THAT NO AILERON CAME UP NO THE R WING. WE CHKED THE L WING AND WE HAD AILERON AND SPOILER COME UP. WE DID HAVE A SPOILER COME UP ONLY ON THE R WING. WE CALLED MAINT AND RETURNED TO THE GATE AND DISCOVERED THE AILERON CABLE HAD BROKEN. THANKS TO THE FO FOR DOING JUST A LITTLE EXTRA WHICH STEMMED FROM HIS CIVILIAN BACKGND ON SMALLER ACFT. BOEING NEEDS TO ADDRESS THIS PROB AS WE FOUND OUT IT WAS NOT THE FIRST OCCURRENCE IN RECENT TIME THAT THIS OCCURRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE FO CHKED THE AILERON DURING THE PRE TKOF FLT CTL CHK AND NOTICED THE R AILERON DID NOT MOVE UP WHEN THE CTL WHEEL WAS TURNED TO THE R. RPTR WAS GRATEFUL THE FO WAS CHKING THE FLT CTLS. ACFT WAS TAXIED BACK TO THE GATE AND MAINT DISCOVERED A BROKEN CABLE THAT MOVES THE AILERON. HE FURTHER STATED THAT MAINT INFORMED HIM THAT THIS TYPE OF FAILURE IS THE THIRD ONE IN THE LAST 2 YRS AT HIS ACR.