1. An engine control system for managing a schedule of execution of engine control tasks comprising: request receiving means for receiving requests to initiate engine control tasks; and scheduling means for scheduling execution of the engine control tasks, when said request receiving means receives the requests, said scheduling means determining a sequence of execution of all the engine control tasks which are requested to be initiated and allocating execution times for which the engine control tasks requested to be initiated are to be executed within a constant reference time frame, said scheduling means performing the execution of the engine control tasks cyclically and altering lengths of the allocated execution times, within the constant reference time frame, depending upon a number of the engine control tasks requested to be initiated.