A B737-700 ACFT FAILED ELEVATOR TAB PWR-OFF 'NULL' CHK WHILE ACFT LNDG GEAR FILLET FAIRINGS WERE BEING EVALUATED FOR CABIN FLOOR VIBRATION.

Narrative

I WAS CALLED OUT TO ACFT X IN HANGAR TO INSPECT THE ELEVATOR TAB ADJUSTMENT. TECHNICIAN MR A HAD HIS TAB READINGS AFTER THE ADJUSTMENT WRITTEN DOWN ON A PIECE OF PAPER. I VERIFIED THE 'B' DIMENSION ON THE HORIZ STABILIZER WITH THE TRAMMEL BAR AND THEN VERIFIED THE TAB POS WITH MR A USING THE DIGITAL ELEVATOR TAB FIXTURE BAR. THEY READ THE SAME AND WERE WITHIN MANUAL LIMITS. MR A THEN TORQUED THE TAB ROD ADJUSTMENT AND ROD END HARDWARE WHICH I WITNESSED. I THEN LEFT THE AREA TO TAKE CARE OF ANOTHER INSPECTION ITEM AND TOLD MR A TO GO AHEAD AND SAFETY THE TAB ROD AND ROD END HARDWARE. I CAME BACK AND DID A SAFETY CHK FINDING THE INBOARD ROD COARSE ADJUSTMENT WITNESS HOLE OF THE R-HAND TAB HAD NO THREAD SHOWING. MR A BROKE THE ROD LOOSE AT THE COARSE ADJUSTMENT AND WENT ONE FULL TURN SHORTER TO FILL THE WITNESS HOLE. HE THEN BROKE THE FINE ADJUSTMENT ROD END LOOSE TO GET A SLIP FIT OF THE BOLT AT THE TAB. HE THEN RETORQUED AND SAFETIED THE HARDWARE; WHICH I WITNESSED. HE THEN INSTALLED THE TAB COVERS AND CLOSED THE AFT ACCESSORY COMPARTMENT. WE THEN SIGNED OFF LOG PAGES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE ORIGINAL VIBRATIONS WERE DUE TO THE LNDG GEAR FILLET FAIRINGS CAUSING THE CABIN FLOOR VIBRATIONS. THE ISSUE SURROUNDING THE ELEVATOR PWR OFF TAB CHK WAS DUE TO THE TEST FLT CREW VERBALLY STATING THE % OF MAC (MEAN AIR CHORD) REQUIRED EXCESSIVE HORIZ STABILIZER TRIM WHEEL TURNS TO FAIR ACFT.