B737-800
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Workload; Confusion; Distraction
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action
Aircraft
While descending through about 7000 ft. MSL in IMC; PM (Pilot Monitoring) noticed his airspeed immediately dropped to 100 kias. PF (Pilot Flying) Airspeed was normal. PM was also PIC. PM immediately pushed power up and closed [the] throttles. At this point I saw the IAS disagree light and determined my IAS was correct. I disconnected [the] autopilot; said my aircraft and attempted to rejoin the STAR. During the event airspeed accelerated to almost 300 kias. We received a frequency change and slowed back to 250 kias. ATC did not notice the airspeed deviation. The CA (Captain) airspeed indicator recovered after about 40 seconds and worked for the remainder of the flight.Something caused the CA airspeed indicator to malfunction. The startle factor caused the Captain to assume [the] worst case and push power up before we were able to determine that his indicator was malfunctioning. By the time we knew all the information we had accelerated above 250 knots.
B737-800 First Officer reported the Captains airspeed indicator malfunctioned on the descent.