EMI problems during system integration of a modern fighter aircraft-a case study

Summary form only given. A modern fighter aircraft is an electronics-intensive weapon platform with attendant EMI problems. The problem is exacerbated by the use of digital fly by wire flight control system, electronics nose wheel steering and brake management systems, and digital engine control systems. All these systems are safety critical and malfunctioning of these systems due to EMI from onboard electronics systems or due to external electromagnetic environment would lead to loss of aircraft. The Indian Light Combat Aircraft (LCA) which incorporates all the modern technologies has to be designed to ensure that the EMI problems are minimised. EMC engineering was adopted as part of the overall aircraft design, fabrication and testing. This includes formulation and implementation of a comprehensive EMI control plan incorporating various EMC guidelines at subsystem level and system level. Special EMC features include a hybrid grounding system using Single Ground Reference Point (SGRP) concept wherein the return current (power and signal) do not flow through the aircraft structure resulting in elimination of the troublesome common mode ground loop coupling at low frequencies. EMC analysis and prediction techniques were used at the early project definition phase for optimum location of all antennas to minimise mutual interference between various RF system onboard aircraft. Test Plan at LRU level conforming to MIL-STD-461C was strictly enforced and waivers were granted only after aircraft level analysis of the effect of waiver on other system. Aircraft level intra system and inter system EMC Tests are now in progress. As a result of systematic EMC analysis, design and test methodologies at various levels, very few EMI problems were observed during aircraft system integration and testing phase which is now in an advanced stage. However, a few problems which were discovered during the system integration were solved using the EMI Fix method. This paper describes the EMC design and analysis techniques adopted, the EMI tests conducted during the system integration phase of LCS, the EMI problems faced during the system integration, analysis of the problems and the solution to the EMI problems.