B757-200
Flight Crew Air Transport Pilot (ATP)
Workload
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; General Declared Emergency
Aircraft; Procedure
Aircraft had four (4) flag MEL items including 27-41-02 Stab Trim Primary Center Channel inop; 22-10-01-C Autopilots All inop; 22-3--01 Autothrottle inop; and 28-22-02-A Center Tank Fuel Pumps inop.  Had flown the same aircraft this morning and had no problem except that the Captain's yoke stab trim was slow; but the alternate trim worked fine (this was covered in the MEL as a possibility).  On descent; passing about 12;000 MSL; the stab trim quit working and stopped at about 4.5.  The alternate trim switches did not work; nor did the First Officer trim switches.  With the other MELs [we] had to hand fly the rest of the approach and landing.  Declared an emergency due to the heavy yoke forces from the out of trim condition.  Landed uneventfully and terminated the emergency.The combination of MELs was the primary factor in the problem.  Before the previous flight the First Officer and I had talked to the Dispatcher and Duty Officer and since the weather was VFR; we decided to fly [the scheduled leg].  I was told that [destination] Maintenance would work on the aircraft during the layover.  However; when we landed the Maintenance Technician indicated that he was not qualified to work on the autopilot system.  Nothing was done during the layover.  After having flown the aircraft on the previous flight and the return weather being VFR; we elected to fly back to [departure station]. Suggestions: Not schedule an aircraft with this many flag MEL items.  The combined effect of the MELs must be considered.  If the weather had been IFR; I would not have taken it for the first flight.  I did feel somewhat pressured to take the aircraft; since there were no spares available.
[Narrative 2 had no additional information]
B757-200 flight crew described operational complications arising from flying the aircraft with multiple MELs.