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An integral part of a new engine certification process is the test verification of satisfactory operation in icing conditions. Icing conditions for this test, which is often conducted at sea level, need to meet or exceed conditions that would be experienced within the flight envelope. In order to assure this fact, manufacturers use analytical tools to conduct a critical point evaluation of engine over the range of flight operation for purposes of comparison to sea level testing. The recent concern for operating in ice crystals places new requirements on icing codes within the industry. One such code is used herein to describe these requirements and to illustrate the critical point evaluation procedure.

Engine manufacturers recognize that either a variable pitch fan blade or a variable area fan nozzle can provide the necessary fan stall/flutter margin to take the next step in engine cycle improvement with enhanced propulsive efficiency and low noise level. The patented Rotating Composite Technologies, LLC variable pitch fan design uniquely offers the same or lower fan hub/tip radius ratio of conventional fixed pitch designs and, with its light weight composite fan blades integrated with an even smaller disk, offers weight savings as well. A variable fan nozzle conversely adds additional weight to the propulsion system and notably will complicate aircraft installation issues relative to competitive manufacturer's engines.