Narrative:

At cruise with autoplt on; FL320; a high speed vibration felt through rudder pedals. I reduced airspeed .84 to .81 and it helped reduce vibration. My captain acted in a mission status -- keep going. I ask that he return. He said there was no vibration; he then tried to determine was it hydraulic or yaw damper related. I was comfortable and encouraged to find this reoccurring problem. Maintenance failed to flight test the aircraft and this problem did not fix itself. Air carrier X maintenance control is pushing the maintenance personnel. No parts are common. Crews take aircraft with sign-offs 'could not duplicate.' maintenance control contacted manufacturer and 'they' made the decision to return. We isolated the problem to not be affected by hydraulics/yaw damper; returned to ZZZ2 and the captain informed dispatch of our new ETA and fuel dumping of 24 tons. We got a satellite call; the captain was told per the fom there was a procedure in the fom and the chief pilot approved us landing overweight. The captain agreed; end of call. I informed the captain he was breaking a far aircraft limitation; we didn't declare an emergency and no one can authority/authorized this; it's a captain's authority/authorized; besides the fellow referred is the director of training. So I told the captain we must dump; he agreed that we could blow tires on landing; a single runway operation. So once again we were forced into a false sense of security that it was ok to break the far's. We dumped fuel and 'did not declare an emergency' and landed normally.

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Original NASA ASRS Text

Title: A B747-400 FO RPTS A RETURN TO LAND WITH RUDDER VIBRATIONS. THE CAPT WAS RELUCTANT TO EXERCISE CAPT'S AUTH AND DUMP FUEL BEFORE LNDG.

Narrative: AT CRUISE WITH AUTOPLT ON; FL320; A HIGH SPD VIBRATION FELT THROUGH RUDDER PEDALS. I REDUCED AIRSPD .84 TO .81 AND IT HELPED REDUCE VIBRATION. MY CAPT ACTED IN A MISSION STATUS -- KEEP GOING. I ASK THAT HE RETURN. HE SAID THERE WAS NO VIBRATION; HE THEN TRIED TO DETERMINE WAS IT HYD OR YAW DAMPER RELATED. I WAS COMFORTABLE AND ENCOURAGED TO FIND THIS REOCCURRING PROB. MAINT FAILED TO FLT TEST THE ACFT AND THIS PROB DID NOT FIX ITSELF. ACR X MAINT CTL IS PUSHING THE MAINT PERSONNEL. NO PARTS ARE COMMON. CREWS TAKE ACFT WITH SIGN-OFFS 'COULD NOT DUPLICATE.' MAINT CTL CONTACTED MANUFACTURER AND 'THEY' MADE THE DECISION TO RETURN. WE ISOLATED THE PROB TO NOT BE AFFECTED BY HYDS/YAW DAMPER; RETURNED TO ZZZ2 AND THE CAPT INFORMED DISPATCH OF OUR NEW ETA AND FUEL DUMPING OF 24 TONS. WE GOT A SATELLITE CALL; THE CAPT WAS TOLD PER THE FOM THERE WAS A PROC IN THE FOM AND THE CHIEF PLT APPROVED US LNDG OVERWT. THE CAPT AGREED; END OF CALL. I INFORMED THE CAPT HE WAS BREAKING A FAR ACFT LIMITATION; WE DIDN'T DECLARE AN EMER AND NO ONE CAN AUTH THIS; IT'S A CAPT'S AUTH; BESIDES THE FELLOW REFERRED IS THE DIRECTOR OF TRAINING. SO I TOLD THE CAPT WE MUST DUMP; HE AGREED THAT WE COULD BLOW TIRES ON LNDG; A SINGLE RWY OP. SO ONCE AGAIN WE WERE FORCED INTO A FALSE SENSE OF SECURITY THAT IT WAS OK TO BREAK THE FAR'S. WE DUMPED FUEL AND 'DID NOT DECLARE AN EMER' AND LANDED NORMALLY.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.