B737-700
Flight Crew Last 90 Days 162
Aircraft Equipment Problem Less Severe
General Maintenance Action
Aircraft
Weather was low overcast with tops around 1400 feet and aircraft ahead of us reported breaking out at 300 feet with winds steady at six knots. Vectors to final approach course for the ILS.  Aircraft configured for landing; on Vtarget speed and completely steady at 1000 feet with autopilot and autothrottles engaged with all checklists complete. Passing 600 feet; the red 'speed tape' on the flight display climbed up within one second to the Vtarget with rudder shakers engaging.  There was no gust of wind felt; no aircraft pitch; roll; or yaw.  The aircraft was completely stable and on speed.  I initiated a stall recovery by adding power and was about to disengage the autopilot when the speed tape receded to its previous position (which provided a good stall margin).  I eased off on the power and the aircraft felt stable and on glide path with speed about Vtarget plus five knots.  Passing 400 feet the speed tape again climbed rapidly to the Vtarget.  The aircraft was still stable in pitch; roll; and yaw with no gusts in the winds.  I again added power to initiate a stall recovery. As speed built; I was about to disengage the autopilot.  The speed tape again receded quickly to a normal indication.   We descended out of the overcast at 350 feet AGL.  The visibility was clear underneath the overcast with the aircraft on glide path for landing with the speed now Vtarget plus 10 KIAS.  The Captain spun the Vtarget speed up 10 knots and stated 'Let's carry 10 extra.'  I disengaged the autopilot; the Captain called 'Approaching minimums' and I replied 'Landing.'  I landed in the touchdown zone with autobrakes three selected; and allowed the autobrakes to slow the aircraft.  Uneventful rollout and taxi to gate.Maintenance called and personally briefed on malfunction with a logbook discrepancy written.
A B737-700 First Officer reported airspeed indicator anomalies; including a stall indicator (rudder shakers) activation; on an ILS approach.