Situational Awareness; Troubleshooting
Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Aircraft Equipment Problem Dissipated; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; General Maintenance Action
Aircraft; Weather
During cruise flight at FL370 Captain's airspeed and altitude disagree indicators illuminated followed by EEC failure to soft mode. Suspected pitot blockage from icing; followed Unreliable Airspeed checklist and EEC procedure in QRH and began descent to FL270. Passing through FL290 all indications returned to normal and remained that way for duration of flight.
The reporter stated that at the time of this event; they were IMC just in the tops of clouds. He stated that the first few minutes of this event were exciting but after the descent was in progress things returned to normal. This event was the third time the Captain's pitot system was unable to prevent ice accumulation so Maintenance replaced the pitot system which corrected the failing.
A B737-800 Captain pitot tube failed to prevent ice accumulation at FL370 resulting in the Captain's Altitude and Airspeed disagree and EEC failure to soft mode. The pitot system was replaced after this event and the third maintenance log entry.