Narrative:

The flight from ZZZ to ZZZ1 was empty ferry flight. In the [flight plan]; 3672 kg of fuel was listed as an extra ballast to reach minimum zero fuel weight of 163838 kg. Our block fuel was 51600 kg. I recall the captain requested 52000 kg as our final fuel load.as I entered the cockpit; the mechanic was just finishing transferring fuel to the center tank. This was unusual since a 52000 kg fuel load should not have any fuel in the center tank. I inquired about it with the captain and he stated the extra fuel in the center tank is for the weight and balance purpose for the takeoff.during the cruise fuel low center left; right advisory messages came on. At the time the captain and I discussed that we do not have any control over extra (ballast) fuel in the center tank since it will eventually scavenge out into main tank 2 and 3. The captain stated the extra fuel in the center tank is for the weight and balance for takeoff cg purpose and not for landing. We continue to ZZZ1 and landed.weeks after this flight; I mentioned about this ferry flight unusual ballast fuel loading to different captain and he suggested to me to look at weight and balance manual.in weight and balance manual; I found the following statement under ballast fuel section: 'the simultaneous loading of ballast and mission fuel in the center tank is not allowed; because there is no indication to the flight crew when to turn off the center tank pumps.''ballast fuel on all company aircraft must be loaded on the main tanks only. Do not load ballast fuel in the center tank. The loading of ballast fuel in the center tank is not allowed; because there is no indication to the flight deck crew when to turn off the center tank pumps.'I looked in the fcom (flight crew operations manual) and [company] fom ballast fuel section(s) since the airplane I ferried was a [company] airplane. However; neither the fcom nor fom have any warnings or statements regarding ballast fuel loading restrictions.thinking about it now; I think I should have researched more about ballast fuel and checked all pertinent company manuals since I rarely do this type of (ferry flight) flight.I recommend fcom sp fuel section and/or fom include all pertinent ballast fuel information and restrictions.

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Original NASA ASRS Text

Title: First Officer reported a conflict regarding the location of fuel used for ballast as stated by maintenance personnel and the operations manual.

Narrative: The flight from ZZZ to ZZZ1 was empty ferry flight. In the [Flight Plan]; 3672 kg of fuel was listed as an extra ballast to reach minimum zero fuel weight of 163838 kg. Our block fuel was 51600 kg. I recall the Captain requested 52000 kg as our final fuel load.As I entered the cockpit; the Mechanic was just finishing transferring fuel to the center tank. This was unusual since a 52000 kg fuel load should not have any fuel in the center tank. I inquired about it with the Captain and he stated the extra fuel in the center tank is for the weight and balance purpose for the takeoff.During the cruise FUEL LOW CTR L; R Advisory messages came on. At the time the Captain and I discussed that we do not have any control over extra (ballast) fuel in the center tank since it will eventually scavenge out into main tank 2 and 3. The Captain stated the extra fuel in the center tank is for the weight and balance for takeoff CG purpose and not for landing. We continue to ZZZ1 and landed.Weeks after this flight; I mentioned about this ferry flight unusual ballast fuel loading to different Captain and he suggested to me to look at Weight and Balance Manual.In Weight and Balance Manual; I found the following statement under Ballast Fuel section: 'The simultaneous loading of ballast and mission fuel in the center tank is not allowed; because there is no indication to the flight crew when to turn off the center tank pumps.''Ballast fuel on all Company aircraft must be loaded on the main tanks ONLY. Do NOT load ballast fuel in the center tank. The loading of ballast fuel in the center tank is not allowed; because there is no indication to the flight deck crew when to turn off the center tank pumps.'I looked in the FCOM (Flight Crew Operations Manual) and [Company] FOM ballast fuel section(s) since the airplane I ferried was a [Company] airplane. However; neither the FCOM nor FOM have any warnings or statements regarding ballast fuel loading restrictions.Thinking about it now; I think I should have researched more about ballast fuel and checked all pertinent company manuals since I rarely do this type of (ferry flight) flight.I recommend FCOM SP Fuel section and/or FOM include all pertinent ballast fuel information and restrictions.

Data retrieved from NASA's ASRS site 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.