B737-800
Aircraft Equipment Problem Critical
General Declared Emergency; General Maintenance Action
Aircraft
Approximately 2 hours into flight during cruise flight at FL380 Airspeed Disagree Caution appeared. The First Officer airspeed display was stuck at approximately 235 KIAS/.74 Mach. After minor adjustments to cruise speed and careful cross checks; it was determined that the Captain's airspeed was properly functioning; but the First Officer airspeed was not. The flight used the satphone to call Dispatch and asked for a conference call with Maintenance to see if any additional information was available; solutions or ideas to correct it; or if any additional concerns might be warranted. Nothing was provided by Maintenance and Dispatch provided an updated VFR weather report for [destination]. As the aircraft began the descent the First Officer's indicated airspeed decreased through the red stall range to 45 KIAS (zero); and the First Officer Altitude Disagree Caution also displayed at this time.Shortly after both of the aircraft engine EEC's went to alternate mode and several related VNAV features and displays went blank; while Autopilot A reverted to CWS for pitch. The First Officer's altimeter continued to descend slower than the Captain's; and the First Officer's primary altitude indication at 8;000 FT MSL was approximately 800-900 FT higher than the Captain's. The flight declared an emergency during descent; and landed on a visual approach without further event. During final approach at approximately 1;000 AGL; the First Officer's instruments returned to normal readings. After landing the Maintenance Representative told us that the aircraft had experienced a similar event that occurred earlier in the month; but this information was not relayed until after the flight had landed. In addition the Maintenance Representative at [destination] had not been notified of the inbound aircraft problems. The logbook write up for the previous event was recorded in an older section of the active logbook; and was not mentioned by Maintenance when the flight called [Operations] requesting assistance.
B737-800 First Officer reported a number of Air Data Computer related failures or malfunctions; including First Officer's airspeed indicator; altitude disagree; EEC to alternate mode; and autopilot issues. Flight declared an emergency and on final everything returned to normal.