MD-80 Series (DC-9-80) Undifferentiated or Other Model
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 8000
Confusion; Troubleshooting
Aircraft Equipment Problem Critical; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control; Flight Crew FLC Overrode Automation; Flight Crew Became Reoriented
Weather; Aircraft
While in cruise at FL310 we were given a descent to FL250. As pilot flying I started down using vertical speed set to 1000 fpm as I wanted to keep our speed at 290 kts. Approaching FL280 Center asked us to expedite through FL270 for traffic. Wanting to stay speed protected I selected IAS mode with 290 kts selected. I retarded to throttles slightly to increase the rate of descent but to keep enough air for the anti-ice system that was activated. The vertical speed indicator showed a rapid increase in descent and I could see the nose was pitched down more than expected. To arrest the descent rate I increased the throttles slightly but that had no effect on the rate of descent. At about this time I said 'What the heck;' and the CA (Captain) started cross checking airspeed indicators. Both FO (First Officer) and CA airspeeds were indicating about 230 kts and aircraft was in a buffet. At the same time the aircraft had begun to capture FL250 and the throttles went forward to accelerate to the speed selected of 290. As the level off continued the autothrottles disengaged. The CA noted that the standby airspeed indicator showed 350 while both primaries showed 230. At level off the CA airspeed indicator moved rapidly from 230 to 350 in about 1 to 2 seconds. The FO airspeed indicator did the same a second or two later. The overspeed warning sounded and I pulled the throttles back to about 60% N1. As the speed slowed the CA called for 80% N1 while we continued to cross check the instruments. Everything stabilized to normal settings. The CA called ZZZ Ops to get Maintenance started as the rest of the flight was uneventful.The entire flight was spent in IMC deviating around a line of weather. I feel both primary pitot tubes collected enough moisture to obstruct airflow until a change in atmospheric pressure or enough ram pressure cleared them. There were no flags on any of the instruments during the entire event. One thing I noticed in vertical speed mode during the initial part of the descent it seemed like the airplane was a little harder than normal to increase the rate of descent. As I added about an extra 200 fpm descent rate it seemed to push against me. I believe it was increasing thrust to maintain the speed selected as we descended.
MD-80 pilot reported both primary airspeed indicators were temporarily incorrect.