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The ARIC 429 is a standard specification for the two-wire data busses that avionic systems use to communicate with each other in commercial airplanes.
The ARINC, which stands for the Aeronautical Radio INC, is a private organization comprising members from the airlines, and manufacturers of aircraft and avionics equipment. The organization promotes standardization of aircraft systems by defining various technical requirements for the aircraft industry.
One of these standards is the ARINC 429; this is also referred to as the MARK 33 DITS specification and is the most widely used data bus specification for the aircraft.
Why are the ARINC 429 specifications important?
The standard specifies the requirements for an avionics communication line in terms of electrical, physical, data format, protocol and other characteristics. This allows compatible avionic systems that range from sensors to computerized control equipment, to communicate with ease regardless of the manufacturer and complexity.
The ARINC 429 allows interoperability and co-existence of different parts from manufacturers. Making it possible for navigation systems, GPS, autopilot, fuel management, climate control, cabinet oxygen control, and computerized systems in an aircraft to interface and talk to one another.
Even though this is a global standard for commercial aircraft, it is not mandatory, and there might be cases where manufacturers develop incompatible components that are not governed by the standard.
Typical characteristics
The ARINC 429 governs the point-to-point data communication bus in which the transmitter connects to one of more receivers through a wired connection. The standard defines the physical, electrical and protocol requirements.
Physical link
The standard recommends a simplex, twisted pair transmission data bus. This comprises of a 78 ohm shielded twisted pair cable. And the cable shield must be grounded at all junctions along the bus and at each of the cable ends to minimize the RF interference.
Electrical characteristics
The standard allows a 10-volt differential voltage; that is +/- 5 volts of the signal voltage. This allowance makes it possible to reliably transmit data that is 5 volts, lower or above, the average signal; - ensuring reliable system communications and operations even at extreme or emergency conditions.
Further, the data encoding is based on the complementary differential bipolar return-to-zero modulation. The BPRZ modulation which helps to reduce the EMI emitted from the cable.
Word length and data format
The data is transmitted in 32-bit words where the actual data or information is transmitted in the 24-bit portion while a label describing the data uses the remaining 8-bit portion.
Data Speed
The standard specifies two data transmission speeds; a low speed of 12.5 kHz and a high speed of 100 kHz with a ± 1% deviation allowed. However, only one rate can be used on a transmission bus.
Advantages
- Allows digital systems in commercial aircraft to communicate with each other using standard data formats and structures over a standard physical communication bus and interfaces
- The universal structures for data and power systems give the designers of aircraft and avionics
systems the freedom to develop and create a wide variety of innovative products.
- Makes it easy to fit new technologies into the existing systems
- Simplifies the designing and implementing complex data and control systems in the aircraft as well as making it easy to maintain, repair and upgrade the systems.
Here you will find the Advantages and Drawbacks of the ARINC 429 Avionics Data Bus Framework.
Applications
The standards are used in various onboard applications in commercial aircraft. The common applications include
- Guidance systems
- Navigation Systems
- Communications
- Flight Control
- In-Flight Entertainment Systems
- Flight Data
Conclusion
The ARNIC 429 standard defines the signal levels, physical characteristics, cables, timing, protocols and other parameters that enable a variety of avionics technologies to talk to each other. This allows development of complex systems to monitor and control a wide range of functions in the aircraft. Further, the ARNIC 429 reduces the workload for the pilot, hence improving reliability and safety of the aircraft.