AN MD-80 ACR CAPT EXPRESSED CONCERN THAT THE TAXI OUT PROCEDURE TO CHECK THE RUDDER IS OFTEN INCORRECTLY PERFORMED; WITH CREWS ALLEGEDLY MISSING THE 'RUDDER TRAVEL UNRESTRICTED' LIGHT. HE RECOMMENDS EMPHASIZING THE PROCEDURE WITH MORE DETAIL.

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DURING TAXI OUT; THE RUDDER UNRESTR LIGHT EXTINGUISHED DURING THE FLT CTL CHK. THE ACFT WAS TAXIED BACK TO THE GATE WHERE MAINT DETERMINED THAT THE SENSING SYS WAS OUT OF CALIBRATION. REPAIRS WERE MADE AND THE ACFT DEPARTED THE GATE 1 HR LATER. I HAVE RPTED THIS MAINT PROB SEVERAL TIMES IN THE PAST. NOW THAT THERE SEEMS TO BE A HEIGHTENED AWARENESS OF MAINT ISSUES; PERHAPS THIS TIME THE DEBRIEF WILL HAVE SOME POSITIVE EFFECT. THE OPERATING MANUALS DO NOT ADDRESS THE NEED TO CHK THE OP OF THE RUDDER TRAVEL UNRESTR LIGHT (TO ENSURE IT REMAINS ILLUMINATED) DURING THE FLT CTL CHK. FEW CAPTS (AND NO FO'S) I'VE TALKED TO ARE AWARE THAT THE LIGHT MAY EXTINGUISH DURING THE TEST OR WHAT IT MEANS IF THAT OCCURS. THE RUDDER CTL CHK TAKES PLACE DURING TAXI OUT WHEN THE CAPT IS NOT NORMALLY LOOKING AT THE OVERHEAD ANNUNCIATOR PANEL. IN BRIGHT SUNLIGHT; WITH SUNGLASSES ON; YOU HAVE TO SHADE THE LIGHT WITH YOUR HAND TO DETERMINE IF IT REMAINS ILLUMINATED DURING RUDDER MOVEMENT. IF THE LIGHT EXTINGUISHES DURING THE RUDDER CTL CHK; IT IS EITHER BECAUSE MECHANICAL TARGETS ARE OUT OF CALIBRATION OR AN ELECTRICAL SENSOR HAS FAILED. EITHER WAY; THE RUDDER CTL SYS IS NOT FUNCTIONING PROPERLY AND THE ACFT IS NOT AIRWORTHY FOR FLT. A CHK OF THE MD80 MAINT DATABASE 'MAY' SHOW HOW MANY TIMES THIS PROB OCCURS -- ALTHOUGH THERE IS NO SPECIFIC CODE FOR THIS MALFUNCTION. WHAT THE DATA WOULDN'T SHOW; HOWEVER; IS HOW MANY FLTS TOOK PLACE 'BEFORE' SOMEONE HAPPENED TO NOTICE A MALFUNCTION THEY WEREN'T WATCHING FOR. THE MD80 IS AN OLD ACFT DEVELOPING OLD ACFT TYPE PROBS. LINE PLTS WHO HAVE BEEN ON THE ACFT FOR A LONG TIME ARE STARTING TO SEE MALFUNCTIONS WE USED TO NOT SEE. THE RUDDER-LIMITING CTL SYS ON THE MD80 IS AN ELECTRICAL/MECHANICAL DEVICE THAT IS SEVERAL DECADES OLD AND HAS A 'RUBE GOLDBERG' DESIGN QUALITY ABOUT IT. IN THE FUTURE; WE WILL PROBABLY SEE THIS MALFUNCTION OCCUR WITH INCREASING FREQ. ADDITIONAL INFO ADDED IN THE APPROPRIATE PLACES OF THE OPERATING MANUALS WOULD BE INSTRUMENTAL IN GETTING THIS FLT CTL MALFUNCTION DETECTED AND FIXED IN A MORE TIMELY MANNER THAN IS PROBABLY TAKING PLACE AT THIS TIME.