According to investigators studying flight data recorders and crew observations from previous engine-loss events, all took place at high altitudes and cold temperatures. Incidents struck regional jet aircraft at median altitudes and temperatures of 29,000 ft. and -32C, while for larger jet transports, medians for most events were at altitudes and temperatures of around 26,000 ft. and -21C. All events occurred near convective clouds and/or thunderstorms, in air significantly warmer than the standard atmosphere and in clouds or visible moisture. Common to all were anomalous TAT readings with no significant airframe icing and no weather radar returns.
To find out exactly what is happening inside the convective systems that most frequently cause core icing, particularly in mid-latitude and tropical regions, an international team plans to conduct the High Ice Water Content (HIWC) test campaign in Darwin, Australia. The team includes NASA, FAA, Environment Canada, Transport Canada, Airbus, Boeing, the U.S. National Center for Atmospheric Research and the Australian Bureau of Meteorology. Also joining the effort will be the European Union's High Altitude Ice Crystals (HAIC) project, which will be contributing a specially configured Falcon 20 research aircraft.
The European effort also builds on the European Aviation Safety Agency's (EASA) High Ice Water Content program, which itself used data collected on a series of flight-test campaigns conducted by Airbus in 2010 in the wake of the Air France 447 A330-200 accident in June 2009. The investigation determined the chain of events leading to the crash began with the “likely” obstruction of the pitot probes by ice crystals. As part of its safety recommendations, the French air accident investigation agency, BEA, proposed in July 2012 that EASA “undertake studies to determine with appropriate precision the composition of cloud masses at high altitude,” and based on these results, modify certification criteria for air data probes. The HIWC/HAIC campaigns are therefore intended to provide better understanding of glaciated icing conditions that could also affect air data probes.
Originally planned for early 2013, the timetable for HIWC was slipped to 2014 after delays to the modification of the NASA Gulfstream II—originally designated as the primary test platform. However, further delays to the Gulfstream modification have forced HIWC planners to consider contingency plans under which the Falcon 20 will become the primary aircraft, possibly flying with a scaled version of a research instrument originally intended for the larger NASA aircraft.