Narrative:

Air carrier flight #XXX las-iah feb/xa/01. Departed XA42, arrived XC33. Aircraft #xyz, B737-300. This statement is in regard to an incident that occurred during flight about 40 mins and 150 NM north of phoenix at FL330. I was the first officer on this flight and it was designated as my leg to fly. After rotation, the captain and myself noticed a low frequency. It did not subside after gear retraction. The captain indicated he had previously flown this aft and experienced a similar vibration. Departure and climb out were completely normal. Once en route, the captain indicated he would contact phx line maintenance via air carrier net while I continued to fly and monitor center frequency. I did not listen in on communication #2 with the captain as center frequency was still quite busy. After a few mins, the captain stated that maintenance instructed us to remove hydraulic power briefly to see if the vibration stopped, thus giving them an indication of a possible loose trim tab. I assumed the captain and maintenance were following a prescribed check and that they were fully aware of all possible ramifications of such a check. The captain asked me to hand fly while he removed hydraulic power. Once removed, the aircraft made no abrupt moves. It was determined that the vibration did not subside and the aircraft began a very slight tendency to bank right at approximately .5 degrees per second. I began a left input of aileron, but was unable to correct the flight path. I assumed the manual reversion was sluggish and increased the input with no result. I was about to add left rudder as we decided to repwr the hydraulics, so I centered the controls. Power was re-established and I corrected the 3-4 degree bank, then squared the flight path with the flight director and re-engaged the #2 autoplt. The flight proceeded to destination normally and arrived at XC40 local. Callback conversation with reporter revealed the following information: the reporter stated he was not happy with the captain's acceding to the maintenance controller's request to turn off 'a' and 'B' hydraulic power to the flight controls for troubleshooting a vibration. The reporter said this request was not in the interest of safety for the passenger and crew.

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Original NASA ASRS Text

Title: A B737-300 IN CRUISE AT FL330 HAS A MAINT CTLR REQUEST CREW TO SHUT OFF HYD PRESSURE TO THE FLT CTLS FOR TROUBLESHOOTING.

Narrative: ACR FLT #XXX LAS-IAH FEB/XA/01. DEPARTED XA42, ARRIVED XC33. ACFT #XYZ, B737-300. THIS STATEMENT IS IN REGARD TO AN INCIDENT THAT OCCURRED DURING FLT ABOUT 40 MINS AND 150 NM N OF PHOENIX AT FL330. I WAS THE FO ON THIS FLT AND IT WAS DESIGNATED AS MY LEG TO FLY. AFTER ROTATION, THE CAPT AND MYSELF NOTICED A LOW FREQ. IT DID NOT SUBSIDE AFTER GEAR RETRACTION. THE CAPT INDICATED HE HAD PREVIOUSLY FLOWN THIS AFT AND EXPERIENCED A SIMILAR VIBRATION. DEP AND CLBOUT WERE COMPLETELY NORMAL. ONCE ENRTE, THE CAPT INDICATED HE WOULD CONTACT PHX LINE MAINT VIA ACR NET WHILE I CONTINUED TO FLY AND MONITOR CTR FREQ. I DID NOT LISTEN IN ON COM #2 WITH THE CAPT AS CTR FREQ WAS STILL QUITE BUSY. AFTER A FEW MINS, THE CAPT STATED THAT MAINT INSTRUCTED US TO REMOVE HYD PWR BRIEFLY TO SEE IF THE VIBRATION STOPPED, THUS GIVING THEM AN INDICATION OF A POSSIBLE LOOSE TRIM TAB. I ASSUMED THE CAPT AND MAINT WERE FOLLOWING A PRESCRIBED CHK AND THAT THEY WERE FULLY AWARE OF ALL POSSIBLE RAMIFICATIONS OF SUCH A CHK. THE CAPT ASKED ME TO HAND FLY WHILE HE REMOVED HYD PWR. ONCE REMOVED, THE ACFT MADE NO ABRUPT MOVES. IT WAS DETERMINED THAT THE VIBRATION DID NOT SUBSIDE AND THE ACFT BEGAN A VERY SLIGHT TENDENCY TO BANK R AT APPROX .5 DEGS PER SECOND. I BEGAN A L INPUT OF AILERON, BUT WAS UNABLE TO CORRECT THE FLT PATH. I ASSUMED THE MANUAL REVERSION WAS SLUGGISH AND INCREASED THE INPUT WITH NO RESULT. I WAS ABOUT TO ADD L RUDDER AS WE DECIDED TO REPWR THE HYDS, SO I CTRED THE CTLS. PWR WAS RE-ESTABLISHED AND I CORRECTED THE 3-4 DEG BANK, THEN SQUARED THE FLT PATH WITH THE FLT DIRECTOR AND RE-ENGAGED THE #2 AUTOPLT. THE FLT PROCEEDED TO DEST NORMALLY AND ARRIVED AT XC40 LCL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE WAS NOT HAPPY WITH THE CAPT'S ACCEDING TO THE MAINT CTLR'S REQUEST TO TURN OFF 'A' AND 'B' HYD PWR TO THE FLT CTLS FOR TROUBLESHOOTING A VIBRATION. THE RPTR SAID THIS REQUEST WAS NOT IN THE INTEREST OF SAFETY FOR THE PAX AND CREW.

Data retrieved from NASA's ASRS site as of July 2007 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.