McDonnell Douglas Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Situational Awareness
Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Flight Crew Landed As Precaution; Flight Crew Diverted
Aircraft
Just prior to descent; got a Level 1 alert: 'Tank 1 Tip Fuel Trapped; 5;800 lbs. of fuel is unusable'; and shortly thereafter; 'Tank 1 Pumps off' and then 'Tank 1 Fuel Qty Low'.  One of the first things I did was select 'Closest Airports'. After consulting the QRH; the First Officer and I discussed the situation. I called a captain jumpseater to the front to assist us. We noticed that the fuel system (in Auto) was transferring fuel and was over 2;000 pounds out of balance and still transferring (2;900 the limit). I subtracted 5.8 from the ETA fuel of 19 and pointed out we'd land with about 13 - 'if all goes well'. But we both agreed that we couldn't see how to manually run the fuel keeping an extra 5.8 in tank 1 and not go either out of balance limits or get dangerously low in a tank or risk flaming out an engine. We agreed to 'figure this out on the ground (at the nearest suitable airport)'. I advised Center that 'We have a fuel system problem and would like to go direct'. Which we did. Landed uneventfully.
[Report narrative contained no additional information.]
DC-10 crew diverted to a nearby airport because of a fuel malfunction that trapped 5;800 pounds of fuel in the tip tank making it unusable.