Method and apparatus for providing a dynamic thrust asymmetry rudder compensation command with no direct thrust measurement

A method and apparatus for producing a dynamic thrust asymmetry airplane rudder compensation command with no direct thrust measurement is disclosed. An excess thrust estimate based on measured acceleration along the flight path of the airplane and measured vertical speed of the airplane is low pass filtered (11) to attenuate noise from the inertially derived data. The low pass filtered data is further filtered by a washout filter (15) to produce data that is sensitive only to changes in the excess thrust estimate. The input to the washout filter is frozen (13) and the output of the washout filter reduced to zero if the go-around or flare modes of the control system of the airplane are active or if the thrust asymmetry compensation feature of the primary flight computer is armed. The output of the washout filter is also zeroed when both engines are running, or multiplied by either -1 or +1 when one engine is out. Whether the multiplication is by -1 or +1 depends upon which engine is out. The result is a rudder compensation command that is limited to prevent an excessive rudder compensation command from being produced.