Narrative:

We were cleared direct to an arrival waypoint and to descend via the RNAV arrival. We were in the weather and had the engine anti-ice switches on. Passing 18;000 ft; I called for the descent checklist. As we accomplished the checklist; my first officer said; 'whoa look at your airspeed.' I looked down as we got a buffet alert on the FMC and an aural airspeed low warning and saw about 120. I disengaged all automation; but continued to comply with the RNAV ground track and altitude restrictions. My first officer then made a great call; 'my airspeed's fine indicating 250 KTS.' about that time; we had a master caution light and noted that both eecs had gone into the soft alternate mode. We followed the QRH and; when we put the eecs into the hard alternate mode; my correct airspeed indications came back. The rest of the flight was uneventful. When we landed; maintenance found an adiru fault in both engines and grounded the aircraft. I think crews need to know that this could possibly happen with incorrect data inputs to the engines. The airspeed low warning definitely got my attention; but good pilot not flying skills by my first officer allowed us to properly handle the problem quickly. We initially thought something might have iced up in the weather; but the anti-ice was on and maintenance told us the faulty airspeed indication was due to the eec problem. The issue was loss of accurate airspeed indication on captain's side.

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Original NASA ASRS Text

Title: A B737-800 had a dual ADIRU fault in icing conditions during descent which resulted in both engine EEC's reverting to the Soft Mode and the Captain's airspeed falling to about 120 KTS with a buffet alert and aural low speed warning.

Narrative: We were cleared direct to an arrival waypoint and to descend via the RNAV Arrival. We were in the weather and had the engine anti-ice switches on. Passing 18;000 FT; I called for the Descent Checklist. As we accomplished the checklist; my First Officer said; 'Whoa look at your airspeed.' I looked down as we got a buffet alert on the FMC and an aural airspeed low warning and saw about 120. I disengaged all automation; but continued to comply with the RNAV ground track and altitude restrictions. My First Officer then made a great call; 'My airspeed's fine indicating 250 KTS.' About that time; we had a Master Caution light and noted that both EECs had gone into the soft alternate mode. We followed the QRH and; when we put the EECs into the hard alternate mode; my correct airspeed indications came back. The rest of the flight was uneventful. When we landed; Maintenance found an ADIRU fault in both engines and grounded the aircraft. I think crews need to know that this could possibly happen with incorrect data inputs to the engines. The airspeed low warning definitely got my attention; but good pilot not flying skills by my First Officer allowed us to properly handle the problem quickly. We initially thought something might have iced up in the weather; but the anti-ice was on and Maintenance told us the faulty airspeed indication was due to the EEC problem. The issue was loss of accurate airspeed indication on Captain's side.

Data retrieved from NASA's ASRS site as of July 2013 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.