(R) Electronic Engine Control Design Guide for Electromagnetic Environmental Effects
|Publication Date:||1 February 2020|
The purpose of this document is to provide reference material for establishing compatibility of electronic gas turbine engine control systems and associated components with the electromagnetic environment and achieving compliance with associated airworthiness requirements.
The modern gas turbine engine used for aircraft propulsion is equipped with an ever increasing variety of electrical and electronic systems which provide for engine control, instrumentation, and auxiliary functions.
Today's aircraft engines currently in service or in development employ full authority digital engine control (FADEC) systems. The criticality of the electronics employed in these systems, with regard to continued safe operation of the aircraft, has led to a greater emphasis on ensuring that the equipment is immune to both natural and man-made electromagnetic environments.
Some engine control systems employ electronics in a less than full authority role in the form of "supervisory" or "trimming" controls or limiters. Such systems are still required to be compatible with the electromagnetic environment although the allowable effects on the system and the pass/fail criteria for system testing may differ.
In addition to the control system itself, typical aircraft gas turbine equipment includes many other electronic or electrical devices; these include solenoid operated valves to control anti-icing or environmental air supplies, position indicating and pressure operated switches, ignition systems, permanent magnet alternators, etc. Many engines are also equipped with engine monitoring systems or data concentrator units which provide a digital data bus interface to other aircraft electronic systems.
Signal control and power levels range from a small fraction of a milliwatt to several hundred thousand watts during ignition discharges. Acquiring, understanding, and efficiently applying the assortment of specifications, both civil and military, can be a daunting prospect for the engine component supplier or the equipment designer. Applying stringent electromagnetic compatibility (EMC) requirements to individual components and subsystems may result in unnecessary size, cost, and weight penalties; however, if sufficient margin is not included in early requirements before actual threat levels can be known, the design may not meet final engine level EME requirements. The project engineer or engineering manager is frequently called upon to make decisions and judgments for which some basic knowledge of electromagnetic environmental effects and associated design, test, and certification compliance is essential.
This document aims to be a central source of information, providing reference and guidance material into each electromagnetic phenomenon. The electromagnetic environment is divided into its main constituents, these being:
a. Electromagnetic interference (EMI), including high intensity radiated fields (HIRF)
c. Electromagnetic pulse (EMP)
Within each chapter, the topic is broken down further into the following main sections:
b. Description of the environment
d. Design considerations
e. Compliance methods
A bibliography is provided for those seeking a more detailed treatment of any given topic, and references are made to any appropriate industry specification where applicable.
Electromagnetic compatibility is essentially an air vehicle issue; for a subsystem, such as the engine control, compatibility must be established with other equipment in the aircraft, but it is the complete air vehicle which is exposed to, and must be certified/qualified for, the external HIRF or lightning/EMP threat. A definition of requirements at the subsystem level is required in order to design and test the equipment, prior to the availability of the full-up aircraft, and/or to substitute for full-up aircraft testing. Testing and analysis at the subsystem level is also required in order to achieve engine certification (FAR Part 33 or EASA CS-E) or qualification. However, the subsystem levels are dependent upon other equipment electrically connected to the engine, cable routing and shielding, and the effectiveness of the aircraft structure as an electromagnetic shield.