What is ARINC 429? The most extensive communication standard used in aviation
Introduction to the ARINC protocol
ARINC is an aerospace standard that defines the characteristics of data transference inside aerospace avionic devices. The acronym ARINC is an abbreviation for Aeronautical Radio Incorporated and came into use in 1929. This technical standard was released by the Federal Radio Commission (which later became the Federal Communications Commission) with the purpose of serving as the airline industry's single licensee and coordinator of radio communication.
The protocol has acquired importance as it is the most extensive standard used by most manufacturers. Models should comply with these instructions in order to provide interchangeability. We can currently find it on Airbus A310/A320/A330/A340, Boeing 727,737,747,757,767 or McDonnell Douglas MD- 11.
The protocol defines the physical and electrical interfaces to support an aircraft's avionic local area network. It includes standards for all the different electronic devices in an aircraft such as mission control computers, inertial reference systems, air data systems, altimeters, radios, GNSS, and sensors. Thanks to this, every air data system will provide the barometric altitude as stated by the label 204.
The ARINC standard includes many different specifications regarding all the subsystems, wiring, data buses, and databases used in avionic communications: series 400, 500, 600, 700 and 800. As there are a limited number of labels, it is possible that the same label has different applications or effects depending on its use. According to our previous example, label 204 may be sent by a GNSS sensor or any other sensor providing altitude.
Among all the standards defined in ARINC, the most extensive specification is the ARINC 429.
ARINC-429
ARINC-429 establishes how avionic equipment and systems communicate on commercial aircraft. The specification defines electrical characteristics, word structures and protocol necessary to establish bus communication [1]. This standard became the most extensive and predominant data bus specification in complex avionic systems from the beginning of the XXI century and it expanded its business in aerospace and defense through its ARINC Engineering Services subsidiary. The methods described help reduce the electromagnetic interferences caused by onboard radio elements, cables, electric errors, or electrical interference noises.
Physical Layer & Word Format
The data protocol defines a unidirectional bus formed by two wires (ports TX and RX) that give support to a local network inside the aircraft.
It includes three parts:
- Part 1: Functional descriptions, electrical interfaces, etiquette, word formats (Update nº 18, 11/29/2012).
- Part 2: Discrete standard words (Update nº 16, 01/12/2004).
- Part 3: File transfer techniques (Update nº 19, 06/01/2009).
If we examine in detail the bit codification, ARINC 429 uses bipolar RZ (return to 0) codification. The transmitter voltage levels are +5V, 0V y ‐5V (respect to ground) and +10V, 0V y ‐10V between A and B conductors. On the other hand, the receiver uses bipolar RZ modulations with 3 states: “HI” (+7,5V to +11V range), “NULL” (+0,5V to ‐0,5V range) y “LO” (‐7,5V to ‐11V range) between conductors. [2]
On the other hand, when we analyze the ARINC 429 word format where each word represents a delivered engineering unit, we can see that the data bus is sent in a 32-bit word. The message is sent in different parts - as explained in the picture attached where the ARINC label number is specified in the Label field - so it is critical to understand the rest of the fields inside the message.
The rest of the fields are:
- SDI (Source Destination Identifiers): Used by a transmitter connected to multiple receivers. This field helps to identify which one should receive and process the message. If not needed, the bits may be used for data.
- Data: The information to deliver.
- SSM (Sign Status Matrix): Used to indicate sign or direction and to test if data is valid.
- Parity (odd): Used to detect possible errors inside the message. [3]
UAV Navigation and ARINC-429: POLAR-500 AHRS
UAV Navigation works every day to manufacture products easily integrable and compatible with the rest of subsystems inside aerospace platforms or devices.
Our most advanced AHRS inside the POLAR AHRS family, the POLAR-500 communication protocol includes the ARINC 429 using labels 144 and 152 to perform an accurate pointing transmitting azimuth and elevation.
This compatibility with the ARINC standard makes it, as we have stated in the previous lines, to be able to operate as an Antenna Pointing and Stabilization system, with an integrated Air Data Inertial Reference Unit (ADIRU) easy to integrate with the rest of the aircraft subsystems.
Thanks to the use of the ARINC protocol, the POLAR-500 can be used along with a satellite communication modem and provide azimuth and elevation angles through an ARINC 429 output to a range of antennas from different manufacturers.
