Narrative:

Aircraft center of gravity loading became suspect when we received 'stabilizer green band' EICAS advisory message. The airplane did not like the center of gravity setting and hence; the trim setting for the weight and balance as received in the final manifest during taxi out. The flight manual procedure simply leads you to call maintenance after sternly telling you 'do not take off!' maintenance is spring-loaded to simply assume it is an aircraft sensor error; and then to defer the system. We called dispatch immediately; and asked instead for a phone patch to load planning; and asked them to get operations (or whomever provides load planning the data from operations) to confirm that; yes indeed; the airplane truly was loaded with a center of gravity this far forward. Our concern was that perhaps the plane had been loaded incorrectly (with a further aft center of gravity; as it usually is on these flts at those weights -- something like 23-24% is more common) and that the warning system was working correctly. We felt the plane (weight compression sensors on the landing gear that detect a center of gravity) was perhaps telling us the truth; as it was intended to do; and warning us that the center of gravity was not as we were being told by operations and load planning. For some reason; the airplane sensing system did not like a center of gravity inserted in the FMC forward of about 22% mac. We experimented with 22%; 23%; 24% and found the advisory message disappeared. Perhaps the plane really was loaded more aft than reported. Until we could get that mystery solved; or until maintenance could confirm the weight/balance detecting system was in error; malfunctioning; or inoperative; we were not ready to accept a simple deferral and takeoff -- and perhaps get a surprise pitch-up or inability to rotate for takeoff. Do you see our problem? We didn't know if the plane was telling us the truth; or if load planning was correct and the plane was wrong. We eventually (after far too many phone calls; some of which were dropped by satcom) taxied back to a gate for confirmation from those who loaded the plane and from maintenance as to what had transpired so that we could make a decision to either defer and take off; or start opening cargo holds to see just where the cargo was loaded. We also wondered why 'no fail fuel' had been loaded -- the same question was asked by load planning. He was as perplexed as we were; although I had a feeling the total fuel load probably didn't require it. Load planning did point out that the fuel quantity we were carrying could have some of it loaded in the tail at the proper ratio of tail-center tank fuel; and that would help the center of gravity. Upon return to the gate; the station manager insisted her cargo loaders did in fact load the plane as reported -- with a 15% center of gravity (we wondered why they would do this; as we all consider an aft center of gravity as far more desirable) and she was not going to open cargo holds to check. She had a piece of paper signed by the cargo/bag loaders and that was all the proof she needed. I felt this was kind of an in-your-face-captain attitude; 'we're telling the truth; now take the plane and go fly' was the impression I was getting. Bottom line: 1) the plane; and the pilots; were not comfortable with such a 'forward center of gravity.' 2) the flight manual procedure would lead one to believe the problem is always a maintenance problem -- an error in the center of gravity sensing system -- and not perhaps a true cargo/fuel/bags loading problem and an incorrect center of gravity reported to the crew by load planning. 3) there did not seem to be any method to verify the true loading; without opening cargo doors; and yanking out bag containers. I was told peeking in would tell you nothing. 4) all efforts should be toward loading a more aft center of gravity (the airplane seems to be more content with those -- it obviously rebelled at a very far forward center of gravity in our case); especially for long international flts (ours was over 13 hours). After all; we are trained that an aft center of gravity is far preferable; as it reduces trim drag; and hence; increases miles per gallon.5) the delays in this case could have been made shorter if the crew could have been assured the center of gravity was correct and/or the aircraft sensing system was incorrect sooner. I do not have a solution for either of those problems. 6) the flight manual needs to suggest that perhaps the advisory message could be correct -- call dispatch and load planning and get help to ascertain if the center of gravity really is where you were told that it is; before you go taking off with a sensor system that could be telling you the truth! 7) maintenance is a little too quick to defer. I guess they assume by the time you call them; you're convinced the plane is broken; and it's either fix it; of defer it; or stop/don't fly it. There just may be other circumstances that could cause the advisory message that we receive.

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Original NASA ASRS Text

Title: B747-400 RECEIVES STABILIZER TRIM GREEN BAND WARNING ON TAXI OUT. FLT CREW DELAYS DEP TO DETERMINE PROPER CTR OF GRAVITY.

Narrative: ACFT CTR OF GRAVITY LOADING BECAME SUSPECT WHEN WE RECEIVED 'STABILIZER GREEN BAND' EICAS ADVISORY MESSAGE. THE AIRPLANE DID NOT LIKE THE CTR OF GRAVITY SETTING AND HENCE; THE TRIM SETTING FOR THE WT AND BAL AS RECEIVED IN THE FINAL MANIFEST DURING TAXI OUT. THE FLT MANUAL PROC SIMPLY LEADS YOU TO CALL MAINT AFTER STERNLY TELLING YOU 'DO NOT TAKE OFF!' MAINT IS SPRING-LOADED TO SIMPLY ASSUME IT IS AN ACFT SENSOR ERROR; AND THEN TO DEFER THE SYS. WE CALLED DISPATCH IMMEDIATELY; AND ASKED INSTEAD FOR A PHONE PATCH TO LOAD PLANNING; AND ASKED THEM TO GET OPS (OR WHOMEVER PROVIDES LOAD PLANNING THE DATA FROM OPS) TO CONFIRM THAT; YES INDEED; THE AIRPLANE TRULY WAS LOADED WITH A CTR OF GRAVITY THIS FAR FORWARD. OUR CONCERN WAS THAT PERHAPS THE PLANE HAD BEEN LOADED INCORRECTLY (WITH A FURTHER AFT CTR OF GRAVITY; AS IT USUALLY IS ON THESE FLTS AT THOSE WTS -- SOMETHING LIKE 23-24% IS MORE COMMON) AND THAT THE WARNING SYS WAS WORKING CORRECTLY. WE FELT THE PLANE (WT COMPRESSION SENSORS ON THE LNDG GEAR THAT DETECT A CTR OF GRAVITY) WAS PERHAPS TELLING US THE TRUTH; AS IT WAS INTENDED TO DO; AND WARNING US THAT THE CTR OF GRAVITY WAS NOT AS WE WERE BEING TOLD BY OPS AND LOAD PLANNING. FOR SOME REASON; THE AIRPLANE SENSING SYS DID NOT LIKE A CTR OF GRAVITY INSERTED IN THE FMC FORWARD OF ABOUT 22% MAC. WE EXPERIMENTED WITH 22%; 23%; 24% AND FOUND THE ADVISORY MESSAGE DISAPPEARED. PERHAPS THE PLANE REALLY WAS LOADED MORE AFT THAN RPTED. UNTIL WE COULD GET THAT MYSTERY SOLVED; OR UNTIL MAINT COULD CONFIRM THE WT/BAL DETECTING SYS WAS IN ERROR; MALFUNCTIONING; OR INOP; WE WERE NOT READY TO ACCEPT A SIMPLE DEFERRAL AND TKOF -- AND PERHAPS GET A SURPRISE PITCH-UP OR INABILITY TO ROTATE FOR TKOF. DO YOU SEE OUR PROB? WE DIDN'T KNOW IF THE PLANE WAS TELLING US THE TRUTH; OR IF LOAD PLANNING WAS CORRECT AND THE PLANE WAS WRONG. WE EVENTUALLY (AFTER FAR TOO MANY PHONE CALLS; SOME OF WHICH WERE DROPPED BY SATCOM) TAXIED BACK TO A GATE FOR CONFIRMATION FROM THOSE WHO LOADED THE PLANE AND FROM MAINT AS TO WHAT HAD TRANSPIRED SO THAT WE COULD MAKE A DECISION TO EITHER DEFER AND TAKE OFF; OR START OPENING CARGO HOLDS TO SEE JUST WHERE THE CARGO WAS LOADED. WE ALSO WONDERED WHY 'NO FAIL FUEL' HAD BEEN LOADED -- THE SAME QUESTION WAS ASKED BY LOAD PLANNING. HE WAS AS PERPLEXED AS WE WERE; ALTHOUGH I HAD A FEELING THE TOTAL FUEL LOAD PROBABLY DIDN'T REQUIRE IT. LOAD PLANNING DID POINT OUT THAT THE FUEL QUANTITY WE WERE CARRYING COULD HAVE SOME OF IT LOADED IN THE TAIL AT THE PROPER RATIO OF TAIL-CTR TANK FUEL; AND THAT WOULD HELP THE CTR OF GRAVITY. UPON RETURN TO THE GATE; THE STATION MGR INSISTED HER CARGO LOADERS DID IN FACT LOAD THE PLANE AS RPTED -- WITH A 15% CTR OF GRAVITY (WE WONDERED WHY THEY WOULD DO THIS; AS WE ALL CONSIDER AN AFT CTR OF GRAVITY AS FAR MORE DESIRABLE) AND SHE WAS NOT GOING TO OPEN CARGO HOLDS TO CHK. SHE HAD A PIECE OF PAPER SIGNED BY THE CARGO/BAG LOADERS AND THAT WAS ALL THE PROOF SHE NEEDED. I FELT THIS WAS KIND OF AN IN-YOUR-FACE-CAPT ATTITUDE; 'WE'RE TELLING THE TRUTH; NOW TAKE THE PLANE AND GO FLY' WAS THE IMPRESSION I WAS GETTING. BOTTOM LINE: 1) THE PLANE; AND THE PLTS; WERE NOT COMFORTABLE WITH SUCH A 'FORWARD CTR OF GRAVITY.' 2) THE FLT MANUAL PROC WOULD LEAD ONE TO BELIEVE THE PROB IS ALWAYS A MAINT PROB -- AN ERROR IN THE CTR OF GRAVITY SENSING SYS -- AND NOT PERHAPS A TRUE CARGO/FUEL/BAGS LOADING PROB AND AN INCORRECT CTR OF GRAVITY RPTED TO THE CREW BY LOAD PLANNING. 3) THERE DID NOT SEEM TO BE ANY METHOD TO VERIFY THE TRUE LOADING; WITHOUT OPENING CARGO DOORS; AND YANKING OUT BAG CONTAINERS. I WAS TOLD PEEKING IN WOULD TELL YOU NOTHING. 4) ALL EFFORTS SHOULD BE TOWARD LOADING A MORE AFT CTR OF GRAVITY (THE AIRPLANE SEEMS TO BE MORE CONTENT WITH THOSE -- IT OBVIOUSLY REBELLED AT A VERY FAR FORWARD CTR OF GRAVITY IN OUR CASE); ESPECIALLY FOR LONG INTL FLTS (OURS WAS OVER 13 HRS). AFTER ALL; WE ARE TRAINED THAT AN AFT CTR OF GRAVITY IS FAR PREFERABLE; AS IT REDUCES TRIM DRAG; AND HENCE; INCREASES MILES PER GALLON.5) THE DELAYS IN THIS CASE COULD HAVE BEEN MADE SHORTER IF THE CREW COULD HAVE BEEN ASSURED THE CTR OF GRAVITY WAS CORRECT AND/OR THE ACFT SENSING SYS WAS INCORRECT SOONER. I DO NOT HAVE A SOLUTION FOR EITHER OF THOSE PROBS. 6) THE FLT MANUAL NEEDS TO SUGGEST THAT PERHAPS THE ADVISORY MESSAGE COULD BE CORRECT -- CALL DISPATCH AND LOAD PLANNING AND GET HELP TO ASCERTAIN IF THE CTR OF GRAVITY REALLY IS WHERE YOU WERE TOLD THAT IT IS; BEFORE YOU GO TAKING OFF WITH A SENSOR SYS THAT COULD BE TELLING YOU THE TRUTH! 7) MAINT IS A LITTLE TOO QUICK TO DEFER. I GUESS THEY ASSUME BY THE TIME YOU CALL THEM; YOU'RE CONVINCED THE PLANE IS BROKEN; AND IT'S EITHER FIX IT; OF DEFER IT; OR STOP/DON'T FLY IT. THERE JUST MAY BE OTHER CIRCUMSTANCES THAT COULD CAUSE THE ADVISORY MESSAGE THAT WE RECEIVE.

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.