A NUMBER OF B737 AND DC9 ACFT OVERHAULED BY ACR MAINT HAD FLT CTL CABLES TENSIONED WITH IMPROPERLY CALIBRATED INSTS.

Narrative

ON AUG/XA/99; ENGINEERING DEPT NOTIFIED US THAT THE CABLE TENSIOMETERS MAY HAVE BEEN INCORRECTLY CALIBRATED BY THE ACR INST SHOP SINCE 1993. THESE TENSIOMETERS ARE USED TO CALIBRATE ACR ACFT. I WAS THE LEAD MECH FOR SOME OF THE MECHS DOING THIS CALIBRATION. ENGINEERING AND QUALITY ASSURANCE ARE PRESENTLY INVESTIGATING THIS ISSUE. MGMNT HAS BEEN AWARE FROM THE BEGINNING OF THE PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT AT THE PRESENT TIME; ALL OF THE TENSIOMETERS ARE NOW BEING SENT TO AN OUTSIDE VENDOR FOR CALIBRATION. THE RPTR SAID THE SHOP WAS USING A HYD RAM TYPE OF UNIT TO PUT TENSION ON A CABLE AND THE TENSIOMETER WAS CALIBRATED USING THE HYD RAM PRESSURE INDICATOR. THE RPTR SAID THE HYD RAM LEAKED AND THE PRESSURE INDICATOR WAS INACCURATE. THE RPTR STATED THAT UNKNOWN TO THE ENGINEERING DEPT BOEING CHANGED THE MIL SPEC USING THE HYD RAM METHOD OF CALIBRATING THE TENSIOMETERS. THE RPTR SAID THE VENDORS ARE STILL USING A HANGING WT TYPE OF INST WHICH STILL CAN INDUCE ERRORS. THE RPTR SAID THE NEW EQUIP HAS BEEN ORDERED AND THE MAINT MANUAL UPDATED. CALLBACK CONVERSATION WITH RPTR ACN 445055 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE PRESENT TENSIOMETERS ARE BEING CALIBRATED BY AN OUTSIDE VENDOR WHO IS USING THE HANGING WT METHOD THAT IS MAYBE WITHIN 10 LB ACCURACY. THE RPTR SAID THE HYD RAM METHOD IS THE MOST ACCURATE WAY TO CALIBRATE THESE INSTS BUT THE UNIT USED IN THE SHOP IS WORN OUT AND LEAKING. THE RPTR STATED THE NEW EQUIP NOW ON ORDER HAS A 1 LB MARGIN OF ERROR WHERE THE OLD UNIT WAS +/-10 LBS. THE RPTR STATED THE BIGGEST PROB IN GETTING ACTION OVER ALL THESE YRS WAS THE SHOP SUPVR WHO WANTED TO MAKE NO CORRECTIONS. THE RPTR SAID SOME MECHS WHO RPT FROM THE OVERHAUL DOCKS THAT AFTER USING A TENSIOMETER THE CABLES ARE DROOPING AND ARE THEN RIGGED TO WHAT FEELS RIGHT. THE RPTR SAID THE MANUAL FOR CALIBRATION HAS NOT BEEN REVISED SINCE 1980.