Md-80 flight crew experienced a faulty airspeed indicator.

Narrative:

In IMC; fl 320; moderate chop (borderline moderate turb); captain's (ca) window (L1) started to ice up. (Repeat write up) we had all the anti-ice on and the meter sel positions all showed positive current. We were focused on that item.we had been cleared to descend via the RNAV arrival.first officer (first officer) advised me that the autopilot had kicked off. I thought that it had kicked off due to the moderate chop. I took the controls and maintained wings level; climbed back up to altitude (100 feet) and maintained our (on ca's indicator) speed of about 280 knots. I tried to re-engage the autopilot and noticed that the auto throttles had kicked off too. First officer called out 'you are slow' I replied something to the effect 'my speed is good; 280.' he called again and I (we) began trying to identify which airspeed indicator was lying to us; if any. We realized that the first officer and stby air speed indicators agreed and that we were at or below 210 knots. I began to add power. It happened very quickly and was pretty confusing. The first officer called for a descent right as we got just a touch (tickle) of low speed airframe buffet. I added more power and lowered the nose (we had been cleared for the descent).we advised ATC that we were descending and that we would be un-able the RNAV. They cleared us to 11000 feet. At 11000 feet; we changed controls and the first officer flew the approach.

Original NASA ASRS Text

Title: MD-80 flight crew experienced a faulty airspeed indicator.

Narrative: In IMC; FL 320; Moderate chop (borderline Moderate Turb); Captain's (CA) window (L1) started to ice up. (Repeat write up) We had all the anti-ice on and the Meter Sel positions all showed positive current. We were focused on that item.We had been cleared to descend via the RNAV arrival.First Officer (FO) advised me that the Autopilot had kicked off. I thought that it had kicked off due to the moderate chop. I took the controls and maintained wings level; climbed back up to altitude (100 feet) and maintained our (on CA's indicator) speed of about 280 knots. I tried to re-engage the autopilot and noticed that the auto throttles had kicked off too. FO called out 'You are slow' I replied something to the effect 'My speed is good; 280.' He called again and I (we) began trying to identify which airspeed indicator was lying to us; if any. We realized that the FO and Stby Air Speed indicators agreed and that we were at or below 210 knots. I began to add power. It happened very quickly and was pretty confusing. The FO called for a descent right as we got just a touch (tickle) of low speed airframe buffet. I added more power and lowered the nose (we had been cleared for the descent).We advised ATC that we were descending and that we would be un-able the RNAV. They cleared us to 11000 feet. At 11000 feet; we changed controls and the FO flew the approach.

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.

Attributes
ACN	1359154
Time
Date	201605
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Airspeed Indicator
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Speed All Types Inflight Event / Encounter Other / Unknown