Electrical wiring interconnect system (EWIS) is both a concept and practice encompassing every wire, cable, harness, connector, terminal, attachment and allied electrical device installed anywhere in the airplane to transmit electrical energy, data and signals between intended termination points. EWIS therefore underlies power distribution, avionics, lighting, control and communication networks, and its disciplined treatment as a single system is vital to safe, reliable aircraft operation and maintenance.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is an EWIS in aviation?
EWIS stands for Electrical Wiring Interconnection System, which embraces wires, cables, harnesses, connectors, terminals, attachments, and all other electrical devices found on aircraft as part of a system. Electrical wiring interconnection system (EWIS) means any wire, wiring device, or combination of these, including termination devices, installed in any area of the airplane for the purpose of transmitting electrical energy, including data and signals, between two or more intended termination points. The term originated in the aviation industry but was originally designated as Electrical Interconnection Systems (EIS); the change was done to emphasize the focus on the actual wires and wiring of the systems throughout aircraft.
Why is EWIS important in aviation?
EWIS is important in aviation because the performance and safety of an aircraft are dependent upon the integrity of the electrical system. Faults in wiring cause equipment failures, in-flight fires, or complete system shutdowns; therefore, every harness and connector must remain rugged and reliable from first flight to retirement.
The Swissair Flight 111 accident involved wiring failure, and TWA Flight 800 accident was caused by explosion of the center wing fuel tank resulting from ignition of the flammable fuel/air mixture in the tank. These events prove that a single degraded wire endangers the entire aircraft, making disciplined selection, installation, inspection and maintenance of electrical components a life-or-death matter.
What are the components of EWIS?
The components of EWIS are listed below.
- Wires, cables, and bus bars
- Termination points on electrical devices
- Connectors, and connector accessories
- Electrical grounding and bonding devices and their connections
- Electrical splices
- Wire protection materials, including insulation, sleeving, and conduits
- Shields or braids
- Clamps and other devices used to route and support the wire bundle
- Cable tie devices
- Labels or other means of identification
- Pressure seals
- Shelves, panels, racks, and junction boxes
Correct engineering design, planning and coordination with manufacturers secures proper installation of each part. Extra wire length is supplied to allow at least two re-terminations. For systems for which redundancy is required, EWIS components associated with those systems must be specifically identified with part number, function and separation requirement for bundles.
How is EWIS maintained in aircraft?
EWIS maintenance personnel need to be aware that aircraft EWIS must be maintained with the same level of attention and intensity as any other system in the aircraft. Programme AMC 20-21 is programme to enhance aeroplane EWIS maintenance, and the objective is to enhance the maintenance of aircraft EWIS through adoption of Enhanced Zonal Analysis Procedure (EZAP).
Inspection and maintenance practices focus on keeping wire bundles backed by suitable clamps, grommets, or other devices at intervals of not more than 24 inches (60.96 cm), and stand-offs are used to maintain clearance between EWIS and structure. Regular inspections keep electrical wiring systems reliable for every flight, yet visual inspection of wiring has inherent limitations and small defects like breached or cracked insulation will not always be apparent. To mitigate these issues, live-wire testing can detect intermittent faults that cannot be located during maintenance on the ground, and automated wire system testing has been shown to be effective because it supplies the best data available from Navy Air Systems.
