A B737-200 ON TAXI OUT RPTS THE APU OVERSPD LIGHT ON. ACFT HAS A DEFERRED ITEM ON THE APU FUEL HEATER INOP. THE DISPATCHER AND MAINT HAVE A PROB INTERPING THE MEL AND RENDER THE APU INOP.

Narrative

ACFT WAS DISPATCHED WITH APU FUEL HEAT INOP. ON TAXI OUT; CREW ADVISED DISPATCHER AND MAINT THAT APU HAD OVERSPD AND NEEDED APPROVAL. DISPATCHER CONFERRED WITH MAINT AND AGREED TO USE MEL RELIEF FOR THE APU. SOME QUESTION LATER AROSE AS TO THE LEGALITY OF INOPING THE APU SINCE THE MEL FOR THE APU FUEL HEAT STIPULATES THE APU MUST OPERATE NORMALLY. I BELIEVE; AS DOES MAINT; THE INTENT OF THE STATEMENT WAS TO ALLOW OP OF THE APU WITH THE FUEL HEAT INOP. THE ACFT WAS TAKEN OTS AT THE DEST AND MAINT FERRIED FOR REPAIR OF THE APU. WHILE I BELIEVE NO VIOLATION OCCURRED AND THE INTENT OF THE MEL WAS FOLLOWED; THE INTERP OF THE MEL SEEMS MISLEADING AND IS CURRENTLY UNDER SCRUTINY BY FLT OPS AND MAINT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE ACFT WAS A B737-200 AND RPTED THE APU OVERSPD LIGHT WAS ILLUMINATED. THE RPTR SAID THE ACFT HAD AN OPEN DEFERRED ITEM ON THE APU FUEL HEATER WHICH STATED 'MAY BE INOP PROVIDED THE APU OPERATES NORMALLY.' THE RPTR SAID THE PROB WAS THE OVERSPD LIGHT ON IS NOT CONSIDERED A NORMALLY OPERATING APU AND IS IT THE INTENT OF THE MEL TO ALLOW GND OP IF THE AUTO SHUTDOWN SYS OPERATES NORMALLY. THE RPTR STATED MAINT ADVISED THE ACFT TO RETURN TO THE GATE TO RESET THE OVERSPD WARNING AND IF RESET OK; THEN DISPATCH WITH NORMAL APU OP. THE RPTR SAID THE DEFERRING OF THE APU AS INOP PER THE MEL WAS CHOSEN AND THE ACFT DISPATCHED.