CURRENT RETURN PATH or Electrical Structure Network (ESN) The ESN is a passive metal- lic grounding network made up of thousands of structural elements of the airframe as well as additional conductive components—including ground straps and cables—bonded together and connected to the aircraft’s overall grounding / bonding system. As described in the sidebar, the key function of the network—particularly from the perspective of regulatory agencies—is passenger and crew protection from lightning strike or other surge-currents. The ESN also plays a crucial role in mitigating EMI by helping to direct errant electrical energy away from sensitive systems, again, ensuring the safety of the aircraft and its occupants.
In summary, bonding in aircraft systems plays a vital role in ensuring electrical continu- ity and mitigating EMI. It helps establish electrical continuity between components, creates low-resistance paths for current flow, and enhances the effec- tiveness of grounding systems. Additionally, bonding techniques contribute to EMI mitigation by establishing common electrical reference points, forming ESD dissipation paths, and minimiz- ing the formation of ground loops—essential for maintaining electrical integrity, optimiz- ing system performance, and ensuring the reliable opera- tion of aircraft systems.
Grounding Principles Grounding in aircraft systems is based on the implementa- tion of several fundamental electrical principles: Point of Voltage Reference (PVR): The PVR in aircraft systems is the zero volt refer- ence shared by all aircraft equipment. The neutral of the aircraft’s alternating current (AC) power sources, and the cold point of the aircraft’s direct current (DC) sources, are elec- trically connected to the PVR, serving as a common refer- ence for electrical potential. The PVR is connected to the Earth’s ground during refuelling and ground maintenance, provid- ing a stable and consistent fault current grounding path. Equipotentiality: The principle of equipotentiality ensures that all metallic components that can be touched simul- taneously, or can come into contact during normal opera- tions, are electrically bonded
Transient Voltage Suppression (TVS) Connectors are
another tool used to protect mission-
critical avionic equipment by clamping and diverting excessive energy to ground.
Mission-Critical SYSTEMS Here are some examples of mission-critical systems isolated and protected from voltage surges by the current return path (Electrical Structure Network)
Power Distribution Systems: The power distribution system supplies electrical power for all critical operations on the aircraft. Surge protection is necessary to prevent voltage spikes from interrupting power supplies and damaging electrical equipment on increasingly all-electric aircraft.
Avionics Systems: Avionics encompass a wide range of electronic LRUs, including communication, navigation, and flight management. Avionics provide essential data and functionality for flight operations. Surge protection in avionics equipment helps safeguard sensitive electronics, prevent data corruption, and ensure accurate functioning of critical instrumentation.
Flight Control Systems: These systems, including fly-by-wire control surfaces and related components, are vital for maneuvering and navigating the aircraft during flight. Ground system surge protection is crucial for uninterrupted control and helps prevent fault current malfunctions that could jeopardize flight safety.
QwikConnect • July 2023
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