Overview of Electromagnetic Interference & Compatibility – Aircraft Issues By Mr V.T. Ananda Krishna The author is a consultant at AXISCADES, Bangalore and possesses 35 years of experience in the field of Avionics System Design, Development & Integration activities on various fighter aircraft platforms. He earlier discharged his duties in the capacity of AGM (Electrical & Avionics) at ARDC HAL Bangalore.

Background: The aircrafts currently being designed incorporates Avionics LRUs with the state of the art processors to perform high speed computations to realize Digital fly by wire Flight controls, Navigation, Weapon Stores etc. (applicable to military aircrafts). In this context number of digital signals in the data bus of aircraft wiring is quite large and are more prone to Electromagnetic Interference during operation. The problem becomes more complex during the integration of the aircraft when all the systems are powered on simultaneously. Further some EMI problems are encountered only during the flight trials and not reproducible on the ground. Hence in order to address these issues few guidelines to be followed during the design stage of the aircraft. Sources: The main sources of EMI are identified as Electrical Power Generators & Radio / Radar Transmitters. The typical interference can be categorized as follows. a) Radiated Emission (RE) b) Radiated Susceptibility (RS) c) Conducted Emission (CE) d) Conducted Susceptibility (CS) Design Criteria: Most of the EMI issues are likely due to LRU Design or Electrical wiring implemented on the aircraft which are as follows. LRU Design: Ensure the use of MIL grade components in the LRU hardware which were screened for the compatibility of EMI parameters to provide the required compatibility. Further subjecting the LRU for EMI tests during qualification tests in accordance with the applicable clauses stipulated in the MIL STD 461 will ensure the proper functionality of the hardware interface in the EM environment. However these measures are applicable when the LRU is being tested in the standalone mode.

AXISCADES Overview of Electromagnetic Interference &

Compatibility – Aircraft Issues

Page 2 of 2

Wiring Design: Grounding: Ensure proper grounding of power/signal returns & use of junction modules at various locations on the aircraft. Shielding: Ensure the shields are terminated effectively and no shield to be open ended. This is likely to increase the EMI problems. Performance Analysis: It is essential to monitor the performance of the systems in the integrated mode when the aircraft is equipped with all the systems and powered on in the flight configuration. The Intra & Inter system checks on the aircraft enable full compliance of the EMI/EMI issues. INTRA System Checks: Intra system check to be performed when the aircraft is equipped with all systems and operationalized in the flight configuration & powered ON simultaneously. The abnormal noise in head set or flickering of cockpit display symbologies confirm the interference. This is to be addressed by isolating the individual systems and monitoring the performance. INTER System Checks: Inter system checks to be performed by exposing the aircraft to various levels of radiated emission simulated in the ground by different signal generators and RF transmitters. These checks are essentially to check the compliance with the Radiated Susceptibility (RS) checks and will be in accordance with the MIL Std. 464E. These checks are required to be carried out by identifying the aircraft zone wise and performance of the systems located in the respective zones to be monitored. The above measures and checks ensures the optimum EMI/EMC compliance of the Systems and Aircraft in the ever increasing Electromagnetic environment.