Just wondering if there are any current 747-400 combi operators using ballast fuel.
After the TWA explosion and prior to the new fuel management software/fuel system modifications, an AD was issued in 2002 telling the operators to turn off their CWT pumps prior to the pumps going low pressure. As a result, the scavenge system sometimes didn't work (the float valves in the CWT for the scavenge system didn't let the fuel into the scavenge at these higher CWT fuel levels).
A modification was carried out to the valves according to a Boeing Service Bulletin (keeping them open all the time) i.e. SB 747-28-2255 (Revision 2). This meant that only the fuel level in the main tanks inhibited the scavenge system. This mod, however, meant that any ballast fuel would be sucked out of the CWT. Combi operators would either have to inop their ballast systems (or deactivate their scavenge systems when ballast fuel was required).
These days, the Service Bulletin-modified aircraft still seem to be flying around (even after all the FAA required modifications to the fuel system). Do the combis still have their ballast systems inoped? (unless the scavenge system is deactivated)
Thanks
Rgds
NSEU