The document discusses electromagnetic interference (EMI) issues that can arise in modern aircraft systems. Modern aircraft incorporate many digital systems that increase EMI risks. Sources of EMI include electrical generators and radio/radar transmitters. Design approaches to mitigate EMI include using shielded, military-grade components; rigorous EMI testing of systems; proper grounding and shield termination in wiring; and performing checks of system performance both individually and collectively during aircraft integration and flight testing. These measures help ensure EMI compatibility of aircraft systems in electromagnetic environments.

1. 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.

2. 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.