AN MD90 WAS DISPATCHED WITH A DEFERRED ITEM THAT REQUIRED A CHK OF FULL ELEVATOR TRAVEL PRIOR TO FLT; BUT THE MEL GIVES NO ACCEPTABLE METHOD OF ACCOMPLISHING THIS CHK.

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WE WERE SCHEDULED TO FLY AN MD90 WITH A PYLON FLAP FAULT WARNING THAT HAD BEEN PUT ON MAINT CARRY OVER PER THE ACFT MEL. ONE OF THE CONDITIONS OF THE MEL WAS TO CONFIRM FULL TRAVEL OF THE ACFT ELEVATOR PRIOR TO EACH DEP. WE WERE UNABLE TO CONFIRM FULL TRAVEL OF THE ACFT ELEVATOR DURING OUR PRE-TKOF CTL CHK USING THE 'ELEVATOR AT LIMIT' LIGHT; SO WE RETURNED TO OUR RAMP AND CALLED COMPANY MAINT. COMPANY MAINT TOLD US THAT THEY COULD CONFIRM FULL ELEVATOR TRAVEL VISUALLY; WHICH THEY DID; AND SIGNED OUR ACFT LOGBOOK INDICATING THAT THE REPETITIVE MEL CHK WAS COMPLETED AND THAT WE WERE IN COMPLIANCE WITH THE MEL. WE DEPARTED AND FLEW TO OUR DEST WITHOUT INCIDENT. PRIOR TO DEP ON THE NEXT LEG; WITH THE SAME ACFT; THE COMPANY REQUESTED CONTRACT MAINT TO HELP US WITH THE REPETITIVE CHK REQUIRED TO COMPLY WITH THE MEL. HOWEVER; SINCE THE 'ELEVATOR AT LIMIT' LIGHT WAS NOT WORKING; OUR COMPANY MAINT DIRECTED CONTRACT MAINT TO SATISFY THE FULL RANGE MOVEMENT OF THE ELEVATOR REQUIREMENT BY READING DIGITAL RANGE READOUTS FOUND ON A MAINT ONLY PAGE ON THE ACFT'S MULTI-FUNCTIONAL DISPLAY UNIT. CONTRACT MAINT WAS UNABLE TO CONFIRM FULL RANGE TRAVEL OF THE ELEVATOR USING THIS ALTERNATE METHOD AND THE ACFT WAS TAKEN OUT OF SVC. THE NEXT DAY WE WERE TOLD TO FERRY THE ACFT; ON A FERRY PERMIT; TO A COMPANY MAINT BASE WHERE THE ACFT WAS REPAIRED. WE WERE TOLD THAT THE PROB WITH THE ACFT WAS THAT ONE OF THE ELEVATOR POS SENSORS THAT FEEDS THE ACFT DIGITAL FLT GUIDANCE SYS WAS SENDING ERRONEOUS VALUES; BUT THAT THE ELEVATOR WAS WORKING PROPERLY. I AM CONCERNED THAT WE (THE FLC) MAY HAVE BEEN TOLD BY OUR COMPANY MAINT PERSONNEL THAT AN ACFT WAS SAFE TO FLY; WITHOUT THOROUGHLY INVESTIGATING THE PROB. I ALSO FEEL THAT THE MEL SHOULD INCLUDE MORE DIRECTION ABOUT HOW THE FLC AND MAINT CAN 'APPROPRIATELY' CONFIRM FULL TRAVEL OF THE ELEVATOR WHEN OPERATING WITH A 'PYLON FLAP FAULT' ANNUNCIATED SINCE IT IS OFTEN UNLIKELY THAT THE 'ELEVATOR AT LIMIT' LIGHT WILL WORK IF THE PYLON FLAPS ARE NOT WORKING.