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Elevator feel is provided by the elevator feel computer. Inputs of airspeed (from the elevator pitot
system) and stabilizer position (center of gravity) enable the computer to simulate aerodynamic
forces. Feel is transmitted to the control columns by the elevator feel and centering unit. The feel
computer utilizes system A or B pressure to operate the feel system. Whichever system is providing
higher pressure is the only one utilized by the feel computer.
If either system A or B fails, the computer senses the imbalance, and the FEEL DIFF PRESS Light
illuminates when the flaps are up, The light also illuminates if one of the elevator feel pitot systems
fails or a frozen pitot probe results in a difference in elevator feel computer output pressures. The
feel system operates normally with only one hydraulic system operating.