Description

For a number of years, it has been apparent that the detail design of some gas turbine engines has made them vulnerable to the risk of sudden loss of engine thrust if high densities of small ice crystals are encountered in very cold air. This Ice Crystal Icing (ICI) hazard has not usually resulted in complete engine failure (although there have been such instances) but more than one engine may be affected simultaneously. The risk occurs outside of flight conditions which are currently defined by the regulatory authorities as "icing conditions" and therefore defined as such in the applicable Aircraft Flight Manual (AFM). In the light of evidence found during investigations of in-service occurrences of the phenomenon by engine manufacturers and the relative success of design modifications, which have resolved problems with particular engine types, the main regulatory agencies have been considering how to respond to this situation for a number of years now and have, at various points, issued interim operational guidance.