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In August and November 2004, two Bombardier DHC8-315 aircraft, VH-SBJ and VH-SBW, experienced similar abnormal airspeed indications during flight. At the time, both aircraft were being operated in instrument meteorological conditions in cloud and conditions conducive to icing. Examination of flight data recorder information suggested that the pitot heads had become blocked, most probably by ice, preventing air pressure being sensed by the instruments.

The investigation found that the aircraft maintenance manual contained inadequate guidance regarding the continued airworthiness of the pitot head and associated electrical system and that the Quick Reference Handbook for the DHC8-300 did not contain adequate guidance for the flight crew to resolve the abnormal operation of the aircraft systems.

Following the reported incidents, Bombardier, the manufacturer of the DHC8 series aircraft, published a service letter, DH8-SL-34-023. The service letter advised of new procedures regarding the maintenance of pitot head assemblies and associated electrical connectors.

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