Abstract: A control system, such as for a gas turbine engine, prevents a parameter from exceeding a maximum, steady state limit using a topping loop. The topping loop compares the actual value of the parameter to a transient limit which is initially somewhat lower than the steady state limit, but can vary, at a selected rate, up to a maximum of the steady state limit. The difference between the actual value and transient limit may be used to control the system as the parameter approaches the transient limit. The transient limit, and how it varies, is selected to allow a sufficiently rapid approach of the parameter toward and up to the steady state limit, without overshooting such limit.

Abstract: A control system, such as for a gas turbine engine, prevents a parameter from exceeding a maximum, steady state limit using a topping loop. The topping loop compares the actual value of the parameter to a transient limit which is initially somewhat lower than the steady state limit, but can vary, at a selected rate, up to a maximum of the steady state limit. The difference between the actual value and transient limit may be used to control the system as the parameter approaches the transient limit. The transient limit, and how it varies, is selected to allow a sufficiently rapid approach of the parameter toward and up to the steady state limit, without overshooting such limit.

Abstract: A gas turbine engine control system operates based upon a synthesized value of a parameter upon loss of the actual measured value of the parameter. To provide smooth engine operation upon switchover to the synthesized parameter a fixed trim is applied to the synthesized parameter which, upon switchover, makes the synthesized parameter equal to the last known measured value of the parameter. Thus, the engine will see no sudden change in operation at the instant of switchover. Thereafter the trimmed synthesized parameter changes in value by the same amount as does the untrimmed synthesized parameter.

Abstract: A gas turbine engine control system which regulates fuel flow based upon a schedule which is a function of a primary parameter, such as engine pressure ratio, switches to a schedule based upon a secondary parameter, such as compressor speed, upon the inability to function in the primary parameter mode. Upon switchover to the secondary parameter mode the scheduled value of the secondary parameter is down-trimmed to make it equivalent to the last known good value of the primary parameter so that the engine will not experience a sudden change in power level upon switchover. The down-trim is limited. When the primary mode failure occurs during a transient the down-trim is limited to the difference between a scheduled reference value of the secondary parameter and a value of the secondary parameter calculated immediately preceeding loss of the primary parameter mode and based upon a known relationship between the primary and secondary parameter.