Description

On 19 June 2009 a Boeing 767-300 being operated by LOT Polish Airlines on a scheduled passenger flight from Chicago O’Hare to Warsaw was in the cruise at FL330 in night Instrument Meteorological Conditions (IMC) when the Captain's air speed indicator and altimeter suddenly displayed increased readings and an overspeed warning occurred. The crew responded by commencing a climb and reducing thrust which led to a continuous stall warning until descent to a level 5000ft below the previous cruise level had been made and thrust increased. A diversion to Toronto was made but whilst in the hold whilst in a hold to burn off fuel, thrust was reduced to idle with the AP engaged and ALT hold selected and the stall warning warning system was again activated. Recovery from this then led to a climb above the cleared level and a loss of separation occurred with another aircraft that responded to its TCAS RA to avoid the conflict.

Investigation

An Investigation was carried out by the Canadian TSB. Flight Data Recorder (FDR) data was available for the investigation but the 30 minute Cockpit Voice Recorder (CVR) was not stopped after the in flight events or after landing and was of no use to the Investigation.