Narrative:

I was operating the controls on the flight deck doing a check of the stabilizer trim switches. 2 others were clearing the stabilizer. I had been moving the horizontal stabilizer to the full nose up and nose down limits. The procedure for the check calls for the stabilizer to be placed in the aircraft nose up position, then move the stabilizer toward the aircraft nose down position moving the control column aft until the stabilizer stops moving. At the first attempt at the procedure it did not work properly. One of the two at the tail came to the flight deck and informed me that hydraulic power must be applied to the elevators to work properly. This was not mentioned in the checklist nor did it say how far aft the control column must be moved for the stabilizer to stop moving. Until this time, the stabilizer and elevators were clear of obstruction. Hydraulic power was cleared to the elevators and applied. Now with the stabilizer in the aircraft nose up position, I began moving the stabilizer toward the aircraft nose down position and pulled the control column aft. The elevators moving up, struck the tail stand above, damaging the elevator trailing edges. Not familiar with this procedure, I didn't know that only a small movement of the elevators would stop movement of the stabilizer. Also because the checklist did not mention the need to apply hydraulic power to the elevators and the fact that I had moved the stabilizer to the limits and they were clear of obstruction, never came to mind that they might not now be clear. To correct the situation, placards at the tail were posted warning that more clearance is needed moving elevators with the stabilizer, and additions to the checklist about additional clearance and moving the control column gradually.

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Original NASA ASRS Text

Title: A B747-400 DURING A MAINT CHK INCURRED DAMAGE TO THE L AND R ELEVATORS WHEN STRIKING A TAIL STAND DURING A STABILIZER TRIM CHK.

Narrative: I WAS OPERATING THE CTLS ON THE FLT DECK DOING A CHK OF THE STABILIZER TRIM SWITCHES. 2 OTHERS WERE CLRING THE STABILIZER. I HAD BEEN MOVING THE HORIZ STABILIZER TO THE FULL NOSE UP AND NOSE DOWN LIMITS. THE PROC FOR THE CHK CALLS FOR THE STABILIZER TO BE PLACED IN THE ACFT NOSE UP POS, THEN MOVE THE STABILIZER TOWARD THE ACFT NOSE DOWN POS MOVING THE CTL COLUMN AFT UNTIL THE STABILIZER STOPS MOVING. AT THE FIRST ATTEMPT AT THE PROC IT DID NOT WORK PROPERLY. ONE OF THE TWO AT THE TAIL CAME TO THE FLT DECK AND INFORMED ME THAT HYD PWR MUST BE APPLIED TO THE ELEVATORS TO WORK PROPERLY. THIS WAS NOT MENTIONED IN THE CHKLIST NOR DID IT SAY HOW FAR AFT THE CTL COLUMN MUST BE MOVED FOR THE STABILIZER TO STOP MOVING. UNTIL THIS TIME, THE STABILIZER AND ELEVATORS WERE CLR OF OBSTRUCTION. HYD PWR WAS CLRED TO THE ELEVATORS AND APPLIED. NOW WITH THE STABILIZER IN THE ACFT NOSE UP POS, I BEGAN MOVING THE STABILIZER TOWARD THE ACFT NOSE DOWN POS AND PULLED THE CTL COLUMN AFT. THE ELEVATORS MOVING UP, STRUCK THE TAIL STAND ABOVE, DAMAGING THE ELEVATOR TRAILING EDGES. NOT FAMILIAR WITH THIS PROC, I DIDN'T KNOW THAT ONLY A SMALL MOVEMENT OF THE ELEVATORS WOULD STOP MOVEMENT OF THE STABILIZER. ALSO BECAUSE THE CHKLIST DID NOT MENTION THE NEED TO APPLY HYD PWR TO THE ELEVATORS AND THE FACT THAT I HAD MOVED THE STABILIZER TO THE LIMITS AND THEY WERE CLR OF OBSTRUCTION, NEVER CAME TO MIND THAT THEY MIGHT NOT NOW BE CLR. TO CORRECT THE SIT, PLACARDS AT THE TAIL WERE POSTED WARNING THAT MORE CLRNC IS NEEDED MOVING ELEVATORS WITH THE STABILIZER, AND ADDITIONS TO THE CHKLIST ABOUT ADDITIONAL CLRNC AND MOVING THE CTL COLUMN GRADUALLY.

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.