Narrative:

Approximately 1 hour into the flight; I noticed a message on my side captain (ca) that there was an airspeed disagreement. After checking the caution panel; I also found that there was a second problem indicated by an engine caution light (eec went to alt mode). My airspeed indicator showed about 10-15 kts slower than the first officer (first officer) side. The first officer was the flying pilot at this time. I went through the ep for IAS disagree; then airspeed unreliable. It appeared that the first officer side was working properly but the ca side was reading low. After about ten minutes. The problem went away. We elected to continue with the use of the auto-throttle and auto-pilot on the right side. The same problem came back about an hour later; then went away again. With systems set up for the first officer flying; we had no problems during the climb or cruise (to include a couple cruise climbs and descents.)during the first descent in the cruise phase; both airspeed indicators started malfunctioning with wide swings in airspeed indications of up to 40 kts difference; the nose pitched down; and actual airspeed started increasing (VNAV also kicked off). The airspeed disagree message now showed on both ca and first officer sides. We turned off auto-pilot and auto-throttle; and used the standby airspeed indication because it was the only one that seemed to be working properly. We switched controls to the ca side since the standby airspeed indicator is on that side of the panel. The plane flew fine; but there was a very strong tendency for me to pull the malfunctioning airspeed indicator back into my scan; coupled with the small size of the standby indicator; which made it a challenge to keep the desired airspeed. A short while later; we had to react to a TCAS RA. Weather was VMC in ZZZ; but they were calling possible windshear and were reporting gusty crosswinds. Traffic was heavy coming into ZZZ; so we were getting large vectors and speed changes to put us in line for landing.

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Original NASA ASRS Text

Title: B737NG flight crew reported unreliable airspeed indicators on both the Captain and First Officers side.

Narrative: Approximately 1 hour into the flight; I noticed a message on my side Captain (CA) that there was an airspeed disagreement. After checking the Caution panel; I also found that there was a second problem indicated by an ENG caution light (EEC went to alt mode). My airspeed indicator showed about 10-15 kts slower than the First Officer (FO) side. The FO was the flying pilot at this time. I went through the EP for IAS disagree; then airspeed unreliable. It appeared that the FO side was working properly but the CA side was reading low. After about ten minutes. The problem went away. We elected to continue with the use of the auto-throttle and auto-pilot on the right side. The same problem came back about an hour later; then went away again. With systems set up for the FO flying; we had no problems during the climb or cruise (to include a couple cruise climbs and descents.)During the first descent in the cruise phase; both airspeed indicators started malfunctioning with wide swings in airspeed indications of up to 40 kts difference; the nose pitched down; and actual airspeed started increasing (VNAV also kicked off). The airspeed disagree message now showed on both CA and FO sides. We turned off auto-pilot and auto-throttle; and used the standby airspeed indication because it was the only one that seemed to be working properly. We switched controls to the CA side since the standby airspeed indicator is on that side of the panel. The plane flew fine; but there was a very strong tendency for me to pull the malfunctioning airspeed indicator back into my scan; coupled with the small size of the standby indicator; which made it a challenge to keep the desired airspeed. A short while later; we had to react to a TCAS RA. Weather was VMC in ZZZ; but they were calling possible windshear and were reporting gusty crosswinds. Traffic was heavy coming into ZZZ; so we were getting large vectors and speed changes to put us in line for landing.

Data retrieved from NASA's ASRS site 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.