Date: 201909
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: Cloudy
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pitot/Static Ice System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory; Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During the initial descent; I pulled up the PROG page 2 to monitor the OAT temps as we were in IMC. OAT temps were initially around -48c; coming down through FL280. Observing some impacted snow build up on the wipers; I notified the Captain. We opted to turn on TAI (Thermal Anti-Ice). We were handed off to approach and shortly after; we noticed an IAS DISAGREE on the PFD's. While the probe heat and TAI are different systems; we considered the possibility of ice accumulation and responded accordingly. When the IAS DISAGREE initially appeared; the flag quickly disappeared. There was about a 20 kt difference in airspeed at that time. When the flag came on the second time; we immediately ran the associated QRH; which directed us to the Unreliable Airspeed IAC/QRH. We then notified ATC and were given a vector to the west. At that time; ATC informed us of the severe weather closing in on the air field. Once we were able to determine that the Captain's airspeed was unreliable and the standby and First Officer's airspeed were reliable; we transferred controls; the Captain finished the QRH and notified ATC where we were vectored to the ILS XXR. During the approach; the Captain referenced my PFD to make the appropriate callouts. When the aircraft touched down; there was an approximate 40 kt disagreement. As we were taxiing to the ramp; the ENG annunciation light came on. We looked up to the aft overhead panel and saw both of the EEC ALTN lights illuminated.Once the aircraft was parked; the Captain wrote the aircraft discrepancies up. While describing this issue(s) to Maintenance; The maintenance person told us that our issue was normal. This is; indeed NOT normal.From running the QRH checklist; we were able to determine that the Captain's airspeed was unreliable with airspeed deviations of up to 50 kts. slow but the actual cause is undetermined. We were made aware that this is the second time this aircraft has experienced the IAS DISAGREE message and unreliable airspeed. Therefore; I do not believe weather or icing was a factor as the problem continued in to temperatures well above freezing.Do not place this aircraft back in service until this aircrafts pitot/static systems have been thoroughly inspected and resolved.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew reported failure of pitot-static ice protection system; resulting in unreliable airspeed indication.