B747-400 dispatched with a light fuel load and structural check fuel in the center tank develops an ...

Narrative:

We were dispatched with a non standard fuel load. Total fuel loaded was approximately 64.8 with just under 17.0 in the center tank. The flight manual limitation section notes: fuel in the center tank is allowed only when all main and reserve tanks are full except when center tank fuel is payload or structural. The flight plan did not indicate that the center tank fuel was payload or structural. I challenged the dispatcher and after he checked with load planning the release was amended to include the center tank fuel as structural and could be burned. Once in-flight and after the center tank fuel was burned to approximately 3000 pounds; we configured the fuel system to tank to engine. However; the scavenge pumps in the center tank delivered fuel to tanks #2 and #3. Tanks #2 and #3 began to increase as tanks #1 and #4 decreased. In an attempt to balance the fuel load; I opened the outboard xfeed valves and turned on the override/jettison in tanks #2 and #3. The override fuel pumps would not provide adequate fuel pressure because they were below standpipe fuel level. While we were trying to figure this all out; the outboard xfeed fuel valves were open. Since tanks #1 and #4 are higher than tanks #2 and #3; tanks #1 and #4 provided fuel to all engines further exacerbating the problem. We ended up getting out of balance with an EICAS message 'fuel imbal 2-3.' this whole event occurred during a busy time deviating around thunderstorms and close to the top of descent. Once on the ground; I briefed the duty manager; dispatch; and maintenance. Supplemental information from acn 697541: after completion of flight; captain called me and advised they had a hard time keeping the plane in balance limitations with such a low cleared fuel number; approximately 61.3. Once center tank fuel was burned down to 3.0; captain turned on scavenge pumps to #2 tank; but due to low fuel levels in all main tanks; override pumps were uncovered and they were unable to maintain proper balance.

Original NASA ASRS Text

Title: B747-400 DISPATCHED WITH A LIGHT FUEL LOAD AND STRUCTURAL CHK FUEL IN THE CTR TANK DEVELOPS AN OUT OF LIMITS QUANTITY DIFFERENTIAL BTWN THE INBOARD AND OUTBOARD MAIN TANKS.

Narrative: WE WERE DISPATCHED WITH A NON STANDARD FUEL LOAD. TOTAL FUEL LOADED WAS APPROX 64.8 WITH JUST UNDER 17.0 IN THE CTR TANK. THE FLT MANUAL LIMITATION SECTION NOTES: FUEL IN THE CTR TANK IS ALLOWED ONLY WHEN ALL MAIN AND RESERVE TANKS ARE FULL EXCEPT WHEN CTR TANK FUEL IS PAYLOAD OR STRUCTURAL. THE FLT PLAN DID NOT INDICATE THAT THE CTR TANK FUEL WAS PAYLOAD OR STRUCTURAL. I CHALLENGED THE DISPATCHER AND AFTER HE CHKED WITH LOAD PLANNING THE RELEASE WAS AMENDED TO INCLUDE THE CTR TANK FUEL AS STRUCTURAL AND COULD BE BURNED. ONCE INFLT AND AFTER THE CTR TANK FUEL WAS BURNED TO APPROX 3000 LBS; WE CONFIGURED THE FUEL SYS TO TANK TO ENG. HOWEVER; THE SCAVENGE PUMPS IN THE CTR TANK DELIVERED FUEL TO TANKS #2 AND #3. TANKS #2 AND #3 BEGAN TO INCREASE AS TANKS #1 AND #4 DECREASED. IN AN ATTEMPT TO BAL THE FUEL LOAD; I OPENED THE OUTBOARD XFEED VALVES AND TURNED ON THE OVERRIDE/JETTISON IN TANKS #2 AND #3. THE OVERRIDE FUEL PUMPS WOULD NOT PROVIDE ADEQUATE FUEL PRESSURE BECAUSE THEY WERE BELOW STANDPIPE FUEL LEVEL. WHILE WE WERE TRYING TO FIGURE THIS ALL OUT; THE OUTBOARD XFEED FUEL VALVES WERE OPEN. SINCE TANKS #1 AND #4 ARE HIGHER THAN TANKS #2 AND #3; TANKS #1 AND #4 PROVIDED FUEL TO ALL ENGS FURTHER EXACERBATING THE PROB. WE ENDED UP GETTING OUT OF BAL WITH AN EICAS MESSAGE 'FUEL IMBAL 2-3.' THIS WHOLE EVENT OCCURRED DURING A BUSY TIME DEVIATING AROUND TSTMS AND CLOSE TO THE TOP OF DSCNT. ONCE ON THE GND; I BRIEFED THE DUTY MGR; DISPATCH; AND MAINT. SUPPLEMENTAL INFO FROM ACN 697541: AFTER COMPLETION OF FLT; CAPT CALLED ME AND ADVISED THEY HAD A HARD TIME KEEPING THE PLANE IN BAL LIMITATIONS WITH SUCH A LOW CLRED FUEL NUMBER; APPROX 61.3. ONCE CTR TANK FUEL WAS BURNED DOWN TO 3.0; CAPT TURNED ON SCAVENGE PUMPS TO #2 TANK; BUT DUE TO LOW FUEL LEVELS IN ALL MAIN TANKS; OVERRIDE PUMPS WERE UNCOVERED AND THEY WERE UNABLE TO MAINTAIN PROPER BAL.

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.

Attributes
ACN	697806
Time
Date	200605
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : zdv.artcc
State Reference	CO
Altitude	msl single value : 40000
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 100 flight time total : 17000 flight time type : 1100
ASRS Report	697806
Person 2
Affiliation	company : air carrier
Function	other personnel
ASRS Report	697541
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather
Independent Detector	aircraft equipment other aircraft equipment : eicas
Resolutory Action	none taken : unable
Supplementary
Problem Areas	Company Aircraft
Primary Problem	Aircraft

B747-400 dispatched with a light fuel load and structural check fuel in the center tank develops an out of limits quantity differential between the inboard and outboard main tanks.