Large Transport
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Critical; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem
Aircraft
We were leaving 29;000 feet for 32;000 feet in IMC conditions. Engine and wing heat was on. We just did a pitot heat check a few minutes prior. As we were climbing we get an overspeed warning with the clacker going off and a hard buffet. I immediately disconnected the autopilot and autothrottle. I lowered the nose and added power. I knew there was no way we were overspeeding at that altitude and climbing. I said 'I'm initiating stall recovery procedures.' As we got through the first stall I went through a secondary stall which I knew was coming. Upon getting through the secondary stall I continued descent and prepared the cabin for emergency landing. I had no reliable airspeed indicator working. Even the standby indicator did not look normal or match the feel of the plane. I immediately asked for a chase plane to help with airspeed. They tried to get [another] flight to me. He could not get to me as I was rapidly descending. At 14;000 feet all three airspeeds came back and paired up. We still did not trust them; but they acted normal. Made an emergency landing; which was uneventful.
After deviating around weather for most of the flight in IMC; ATC instructed a climb from FL290 to FL320. During the climb both CA (Captain) and FO (First Officer) airspeed indicators increased from 300 KIAS to 350 KIAS. The overspeed warning and clacker sounded during level off and shortly after a low speed buffet developed. The CA immediately turned off the autopilot and autothrottles and began a descent. We [coordinated with ATC] and were given FL260 initially. During the descent both airspeed indicators decreased. We diverted to [a nearby alternate] continuing the descent. Both airspeed indicators got as low as 200 KIAS. At 14;000 feet both airspeed indicators appeared to correct and agree with the standby airspeed indicator. All pitot heat sensors showed current before and after the event. The approach and landing were uneventful.
Air carrier flight crew reported diverting after experiencing unreliable airspeed readings during climb.