Factual Information
A Boeing 757-224, registration N41140, operated as a scheduled passenger flight from an undisclosed origin to an undisclosed destination. At 05:05 UTC on 20 October 2013, while approximately 80 nautical miles southwest of Dublin, Ireland, the crew encountered an anomalous situation involving unreliable airspeed indications and an erroneous stall warning. The aircraft sustained significant damage, and minor injuries were reported among 4 crew members and 13 passengers.
History of the Flight
According to the report, the flight crew consisted of a Commander (male, aged 59, with 11,606 hours as Pilot-in-Command) and a First Officer. During the flight, the crew observed discrepancies in the indicated airspeed readings. The Flight Data Recorder (FDR) data indicated that the aircraft entered an unusual attitude, and the stall warning system activated incorrectly. The crew executed procedures for unreliable airspeed and stall recovery.
Injuries to Persons
Of the 8 crew and 131 passengers on board, 4 crew members and 13 passengers sustained minor injuries. No fatalities were reported.
Damage to Aircraft
The aircraft suffered significant damage. The nature of the damage is not further specified in the provided excerpt.
Meteorological Information
The meteorological documentation indicated the presence of ice crystals in the atmosphere at the time of the occurrence. The aircraft manufacturer's atmospheric analysis confirmed conditions conducive to ice crystal icing, which can block pitot probes.
Aircraft Systems
The investigation focused on the pitot probe system. The aircraft was equipped with a standard pitot-static system. The stall warning system and the engine indicating and crew alerting system (EICAS) were also examined. The IAS DISAGREE alert, which warns of inconsistent airspeed readings, was triggered during the event.
Analysis
The Air Accident Investigation Unit (AAIU) analysis determined that the pitot probes had become blocked due to ice crystals, leading to erroneous airspeed indications. This blockage caused the stall warning system to activate incorrectly, prompting the crew to respond to a perceived stall that did not exist. The startle factor and crew communication were also considered, but no causal links are explicitly stated in the provided source.
Probable Cause
The report does not provide a single probable cause statement in the provided text. The analysis identifies the blocked pitot probes as a key finding, but no definitive causal conclusion is given.