MD-11
Flight Crew Air Transport Pilot (ATP)
Confusion
Aircraft Equipment Problem Less Severe
Flight Crew Returned To Departure Airport; General Declared Emergency
Aircraft
On climb passing 17;000 FT max airspeed tape dropped from 360 KTS to 285 KTS; also got overspeed warnings.  This event happened 9+ times; max time length was 15 seconds.  In cruise when this happened the throttles started retarding; crew intervention was required.  I decided to select airspeed 280 KTS this way speed tape would not be an issue.  Ran Airspeed Erratic checklist.  We made a SATCOM with SME; Maintenance and Flight Control.  After discussion we felt the best course of action was return to base.  We also declared an emergency. At lower altitudes we turned the AFS override to off and flew manual throttles back to [departure airport].  No other airspeed issues on final.  Weather was clear and we were not in turbulence.  This was a repeat write up!  Did extensive debrief with tech support team.  Maintenance found PSEU and autothrottle issues.
At approximately FL320 the throttles started to retard while still climbing; I immediately pushed them up almost through the over boost bar because the aircraft kept slowing. [I] disconnected the autopilot [and] then leveled off at FL325.  When the aircraft was stabilized; Captain called Maintenance and Operations on the Satcom phone. They tried to troubleshoot the problem. It was determined that there may be some sort of problem with the pitot static system or the FMS; however they thought that the standby airspeed was giving correct information.  The solution was then to disconnect the autothrottle (AFS) and autopilot and fly the aircraft.
MD-11 flight crew reported anomaly that caused multiple false overspeed warnings. They chose to declare an emergency and returned to departure airport.