MD-82
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Aircraft; Weather
Started getting moderate turbulence at FL330. Asked ATC for FL240 since we were approaching TOD. FO started a gradual descent and noticed that the airspeed was slowly decreasing so FO increased the vertical speed down. We cross checked the air speeds and mine was the same as FO's; 235 KIAS and decreasing. Aircraft started a buffet much like the speedbrakes were extended so I cross checked standby airspeed indicator and it read 310 KIAS (actually approaching an over speed). FO decreased the vertical speed. We decided to run the Airspeed Unreliable Quick Action checklist. FO turned autopilot; auto throttle; and FD off. I checked Meter SEL and Heat switch not off. We decided both primary airspeed indicators were faulty. FO transferred control of aircraft to me so I could fly by standby airspeed indicator. FO asked for descent to 10;000 feet. Contacted dispatch; informed FA's; and briefed PAX. ATC cleared us direct to the airport. Several minutes after attaining VMC the primary instruments started to return to normal parameters. Landed without further problems.Fix the airplane. It had numerous write ups.
We were flying at FL330. The anti-ice and pitot heat were on and there were no indications of any anti-ice or pitot heat system failure. We were flying in IMC and we started to pick up ice and turbulence. Captain asked Center for lower. The clearance was for us to descend to 24;000 feet. I was the flying pilot; so I put 1;000 feet down in the vertical speed window. During the descent we started to feel some shaking. At one point the Captain checked the lights (which hang down) and asked about the speed brakes and checked them to make sure they were stowed and they were. I noticed my airspeed was getting slow and I pointed it out to the Captain who confirmed that his airspeed indicator was in agreement. We noticed the speed decreasing to around 235 at that time. Captain noted the standby airspeed and said that it was showing fast (around 300 IAS is what I saw across the cockpit). That made sense to me given that the aircraft should not be slow with the established pitch and power. We started to pick up more of the shaking or buffeting. I turned the autopilot and auto throttles off and smoothly but firmly pitched up a slightly nose high attitude to slow the aircraft. I held the pitch until the aircraft buffeting stopped. A crosscheck of the standby airspeed confirmed that the speed was back in a normal range. I returned the aircraft to normal pitch and power settings. We talked to ATC and continued our descent using the standby instruments. I transferred the control to the Captain because he has a better view of the standby flight instruments. We accomplished Airspeed Unreliable Checklist and nothing fixed the primary airspeed indicator problem. After descending out of the clouds into the clear air; all of the flight instruments starting working properly again and were in agreement. Captain transferred the controls back to me and we landed the aircraft safely. There were no lights on the annunciator panel or aural warnings such as overspeed to alert us to this condition.
MD82 flight crew reported unreliable airspeed indications during descent from FL330. Both primary pitot systems showed signs of icing as airspeed decreased with altitude and showed 235 knots while the standby showed 310 knots. After descending out of IMC; airspeed indications returned to normal.