A300
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance; Aircraft Equipment Problem Dissipated; Flight Crew Requested ATC Assistance / Clarification
Aircraft
Airspeed on final was locked in at 250 knots; could not move the speed/mach control knob from 250 preselected to 170 and aircraft never slowed after Alt* or glide slope * [altitude or glideslope capture].  Decided to do a left 360 east of the runway and tried to slow manually.  Speed control came back after about 3 minutes; normal operations and landing followed.
A300 Captain reports inability to control airspeed/thrust via MCP during approach.  Vectors off the approach course are requested and after several minutes MCP operation returns to normal.