An apparatus comprising: a processor (202, 1012) and a memory (1013, 1014, 1016), the processor (202, 1012) including a model generator configured to: generate an engine load model for an engine using flight information, weather information, passenger information and/or cargo information to predict a load on the engine from an engine subsystem utilization modeled for a flight; incorporate the engine load model into an engine model, the engine model representing engine behavior for the flight; determine a first measure of thrust from the engine and a second measure of fuel flow to the engine using the engine model with the engine load model, the engine load model to modify engine behavior by the predicted load on the engine from the engine subsystem utilization; and generate flight parameters for a flight path using the first measure of thrust and the second measure of fuel flow for the predicted load on the engine based on the engine load model; characterised in that the engine load model includes at least one of: when the engine subsystem comprises one or more electrical subsystems, an electrical load model representative of a generation and a transfer of electrical energy from the engine to the one or more electrical subsystems; when the engine subsystem comprises one or more hydraulic subsystems, a hydraulic load model representative of an amount of power from the engine used to power the one or more hydraulic subsystems; and when the engine subsystem comprises one or more pneumatic subsystems, a pneumatic load model representative of an amount of air that is routed from the engine to the one or more pneumatic subsystems. generate an engine load model for an engine using flight information, weather information, passenger information and/or cargo information to predict a load on the engine from an engine subsystem utilization modeled for a flight; incorporate the engine load model into an engine model, the engine model representing engine behavior for the flight; determine a first measure of thrust from the engine and a second measure of fuel flow to the engine using the engine model with the engine load model, the engine load model to modify engine behavior by the predicted load on the engine from the engine subsystem utilization; and generate flight parameters for a flight path using the first measure of thrust and the second measure of fuel flow for the predicted load on the engine based on the engine load model; characterised in that the engine load model includes at least one of: when the engine subsystem comprises one or more electrical subsystems, an electrical load model representative of a generation and a transfer of electrical energy from the engine to the one or more electrical subsystems; when the engine subsystem comprises one or more hydraulic subsystems, a hydraulic load model representative of an amount of power from the engine used to power the one or more hydraulic subsystems; and when the engine subsystem comprises one or more pneumatic subsystems, a pneumatic load model representative of an amount of air that is routed from the engine to the one or more pneumatic subsystems. when the engine subsystem comprises one or more electrical subsystems, an electrical load model representative of a generation and a transfer of electrical energy from the engine to the one or more electrical subsystems; when the engine subsystem comprises one or more hydraulic subsystems, a hydraulic load model representative of an amount of power from the engine used to power the one or more hydraulic subsystems; and when the engine subsystem comprises one or more pneumatic subsystems, a pneumatic load model representative of an amount of air that is routed from the engine to the one or more pneumatic subsystems.