Narrative:

While at cruise; at approximately takeoff plus 55 minutes; we were at FL320; and M.76. We entered the clouds maybe 5 minutes earlier. We felt the aircraft change attitude and noticed that VNAV was disconnected; along with the altitude (altitude) and auto speed (a/south) readouts not even close. There were the associated 'altitude disagree' and 'a/south disagree' warnings on both displays. My altitude reading was FL312; while the first officer's was still at FL320; but diverging. His auto speed reading was dropping and settled at 190 KTS; plus or minus 20 KTS; while my airspeed was stable. We verified with ATC our altitude; airspeed and ground-speed readouts from him; and he said we were still at FL320; and at a constant speed. Not being sure if we could maintain rvsm; or even close; we asked for a block altitude and received the block FL320-330. We later expanded our request to FL310-330. The co-pilot was hand flying at this point; since the autopilot disconnected. He was flying off his altitude display and my airspeed display at this time; I believe. He was doing a very good job of flying; especially considering we were verifying our instruments with ATC and going with the 'best info' off the most correct readout. At this point; I declared an emergency. I felt we could not maintain rvsm standards; and we had way too much incorrect information to check; cross-cockpit; and as far as we could tell; we had major instrument problems! We checked the overhead panel and verified that all probe heat was on and all switches were in the correct positions. It was during this check; we found the eec (electronic engine control) 'altn' (alternate) lights on in both the engine 1 and 2 switches. We accomplished both the eec fail/altn checklist and the display source checklist. We came out of the clouds and within about 2 minutes the readouts started to return to normal; but we could see that we were going to go back in again. We started down for warmer air and asked for FL240 initially with clearance to deviate as necessary; but we reentered the clouds and the instruments again diverged; so we asked for lower. We ended up at FL200; where the sat (saturation) was -09. We remained clear of the clouds; and were able to remain that way for the duration of the flight. We landed at the planned destination with all instrument readouts seemingly back to normal. It is my opinion [that] had this event occurred during colder weather operations; in the clouds; and/or IMC conditions during the approach and landing phase; this may have resulted in a more serious event! As an aside; we had a jumpseat occupant who said he had been on the 737 for many years and for all our work and checklist work; said he 'could find nothing to add to our efforts'. The first officer was flying the aircraft for the leg and did an outstanding job under the confusing circumstances and landed as the winds were approaching 30 KTS. He did a great cross-wind landing; and I would like to make sure he is commended for his work; assistance and professionalism during this event.

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Original NASA ASRS Text

Title: A B737-800's Captain's altimeter and the First Officer's airspeed as well as both engine's EECs developed anomalous behaviors at FL320 in cruise with all other systems appearing normal. During descent into warmer air the system errors dissipated.

Narrative: While at cruise; at approximately takeoff plus 55 minutes; we were at FL320; and M.76. We entered the clouds maybe 5 minutes earlier. We felt the aircraft change attitude and noticed that VNAV was disconnected; along with the altitude (ALT) and auto speed (A/S) readouts not even close. There were the associated 'ALT disagree' and 'A/S disagree' warnings on both displays. My altitude reading was FL312; while the First Officer's was still at FL320; but diverging. His auto speed reading was dropping and settled at 190 KTS; plus or minus 20 KTS; while my airspeed was stable. We verified with ATC our altitude; airspeed and ground-speed readouts from him; and he said we were still at FL320; and at a constant speed. Not being sure if we could maintain RVSM; or even close; we asked for a block altitude and received the block FL320-330. We later expanded our request to FL310-330. The Co-pilot was hand flying at this point; since the autopilot disconnected. He was flying off his altitude display and my airspeed display at this time; I believe. He was doing a very good job of flying; especially considering we were verifying our instruments with ATC and going with the 'best info' off the most correct readout. At this point; I declared an emergency. I felt we could not maintain RVSM standards; and we had way too much incorrect information to check; cross-cockpit; and as far as we could tell; we had major instrument problems! We checked the overhead panel and verified that all probe heat was on and all switches were in the correct positions. It was during this check; we found the EEC (Electronic Engine Control) 'ALTN' (alternate) lights ON in both the engine 1 and 2 switches. We accomplished both the EEC FAIL/ALTN Checklist and the Display Source Checklist. We came out of the clouds and within about 2 minutes the readouts started to return to normal; but we could see that we were going to go back in again. We started down for warmer air and asked for FL240 initially with clearance to deviate as necessary; but we reentered the clouds and the instruments again diverged; so we asked for lower. We ended up at FL200; where the SAT (saturation) was -09. We remained clear of the clouds; and were able to remain that way for the duration of the flight. We landed at the planned destination with all instrument readouts seemingly back to normal. It is my opinion [that] had this event occurred during colder weather operations; in the clouds; and/or IMC conditions during the approach and landing phase; this may have resulted in a more serious event! As an aside; we had a jumpseat occupant who said he had been on the 737 for many years and for all our work and checklist work; said he 'could find nothing to add to our efforts'. The First Officer was flying the aircraft for the leg and did an outstanding job under the confusing circumstances and landed as the winds were approaching 30 KTS. He did a great cross-wind landing; and I would like to make sure he is commended for his work; assistance and professionalism during this event.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.