What Is ARINC 429?

ARINC 429 is the avionics data bus standard that lets equipment on an aircraft share data such as airspeed, altitude, heading and engine parameters. Its formal title is the Mark 33 Digital Information Transfer System (DITS). It was published by Aeronautical Radio, Incorporated (ARINC), the airline-owned company behind many avionics standards, through the Airlines Electronic Engineering Committee (AEEC). It came into service in the late 1970s and early 1980s on the Boeing 757 and 767 and the Airbus A310 generation, and since 2014 the AEEC work has been administered by SAE Industry Technologies Consortia (SAE ITC).

The bus is simplex: one transmitter drives a shielded twisted pair, and up to 20 receivers listen on it. A receiver can never talk back on the same pair, so two-way traffic needs a second bus running the other way. Each transmitter broadcasts a stream of 32-bit words, and every word starts with a label that says which parameter it carries. Receivers simply pick out the labels they need and ignore the rest.

Electrically, ARINC 429 is differential like RS-422 differential serial links, but it uses bipolar return-to-zero encoding with three levels: HI at about +10 V, NULL at 0 V and LO at about −10 V between the two wires. Every bit returns to NULL halfway through, so the signal carries its own clock, and words are separated by a gap of at least four bit times.

Every ARINC 429 word has the same 32-bit layout. The label is written in octal, and its eight bits are sent most significant bit first, while the rest of the word is sent least significant bit first.

The data field is coded in one of a few ways. BNR is two’s-complement binary for continuous values such as altitude. BCD suits values shown on displays, such as radio frequencies. Discrete words pack individual on/off flags. Larger blocks of data, such as flight plans, travel as a series of words using a file transfer protocol defined in the specification. Label assignments and scaling are set by the specification and by each equipment’s interface control document, so two boxes only work together when both follow the same definitions.

An ARINC 429 link has few parts, which is a large part of its appeal.

ARINC 429 carries most of the routine data on commercial aircraft, and on many military transports and helicopters derived from them. Typical links include:

The strengths of ARINC 429 are simplicity and fault isolation. With one transmitter per bus there is no arbitration or collision, timing is predictable, and a failed receiver cannot block the others. The protocol is easy to certify and has decades of in-service history, so equipment from different suppliers works together.

The limits are speed, direction and weight. At 100 kbit/s a bus carries only a few thousand words a second, every transmitter needs its own cable, and parity detects single-bit errors but corrects nothing. Large modern aircraft therefore moved their backbone to faster networks: ARINC 629 on the Boeing 777, and AFDX, a deterministic switched Ethernet defined in ARINC 664 Part 7, on the Airbus A380 and A350 and the Boeing 787.

ARINC 429 is still widely used, though. Sensors and many line-replaceable boxes still speak it, gateways connect it to AFDX, and new avionics for retrofits and business jets keep it. On military aircraft the equivalent role is usually taken by the command/response MIL-STD-1553 bus.

Outside the avionics boxes themselves, ARINC 429 shows up on test benches, flight simulators, ground support equipment and mission systems that read aircraft data. The computer needs an interface card: ARINC 429 boards come in PCIe, Mini PCIe, PMC and XMC, PC/104 and USB formats, with several channels per board, transmit and receive scheduling, label filtering and time-stamping done in hardware.

On the aircraft, the host computer also has to survive the installation. That means shock and vibration testing, aircraft power to the MIL-STD-704 aircraft power standard, and electromagnetic compatibility testing, which our guide to US military standards covers in more detail. Our military computers list MIL-STD-810H and MIL-STD-461 compliance, and our military and aerospace computing page shows how they are deployed.

We build rugged and military computers with the slot, power and I/O an avionics interface card needs, fit the card your programme specifies, install the drivers and test each channel before the system ships. Tell us your channel count, card format and installation, and we will specify the computer to match.