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Turbine engines are affected by a large variety of weather-related factors. This is the reason for the redundancy requirements that have been determined by different institutions and authorities. The ICAO prescribes the following in Annex 6, 5.1.2:
Single engine aircraft shall only be operated in conditions of weather and light, and over such routes and diversions therefrom, that permit safe forced landing to be executed in the event of engine failure.
A unique problem of many weather factors (e.g. rain, hail, ice buildup) is that they affect all engines of multi-engine aircraft simultaneously. This increases the risk of multiple engines failing (for example, see Chapter 5.1.4). This must be closely considered with relation to ETOPS ratings, for example.
The rating process for new engines takes this danger into account and requires extensive performance verifications through testing rig trials under extreme conditions (Ref. 5.1.1-2). The following table shows typical requirements. The current state of the rating requirements can be looked up in the corresponding regulations, such as military MIL-E-8593 or commercial JAR-E540,790,800.