Understanding ARINC 429 and Its Use in Avionics and Aircraft
ARINC stands for Aeronautical Radio Inc. and represents an organization of Major airlines and aircraft manufacturers. The purpose of this organization is to standardize all equipment used in aircraft. Part of this standardization is ARINC 429, which is one of the important bus systems in vogue for commercial aircraft. The word Bus is short form of Omnibus and in computer and digital systems it means a free data exchange between all components of a computer system. This system involves extensive cabling to have the data exchange system give its optimum efficiency.
Modern aircraft have complex electronics on board. Their purpose is that the entire data on board an aircraft is displayed to the pilot. This is done by a Flight Management computer and a display unit. This data is transmitted through a system of data buses. Data buses facilitate interchange of data with digital and other computerized systems and instruments. This system makes use of a unidirectional bus standard called the Mark 33 Digital Information Transfer System (DITS).
As already pointed out one of the important bus connections in a modern aircraft is ARINC 429. This is a two wire differential bus. That means that it connects a single transmitter to one or more receivers. The ARINC 429 will send or transmit data in packets of 32 bits at a speed of 100 kilobits per second. This will make the information appear in real time to the pilot, who really needs this information. This system is installed in most modern airliners like Boeing 737,747,757 and Airbus A 310, 320 and 330. The clue to ARINC 429 is the cabling, thus the latest aircraft use enhanced bus specifications to reduce the size length and corresponding weight of the cabling. This is one of the challenges for designers of aircraft and its importance cannot be underestimated.
ARINC messages generally consist of 32-bit data word. These data words are always 32 bits and consist of five field parity namely SSM, Data, SDI and Label. ARINC 429 has two speeds of data transfer, a low speed (12-14.5 Kb/s) for low critical applications and high speed bus for transferring large and critical data. Another point that must be mentioned is that ARINC429 has no means of error correction and can only communicate error detection. An error once observed will require manual or other methods for correction.
There have been further developments and there have emerged the ARINC 629 and MIL 1553B. Whereas the ARINC 429 operated from a single source and multiple sinks, the ARINC 629 and the MIL 1553B operates from multiple sources and multiple sinks.
In addition the highest rate of data transfer for an ARINC 429 is 100 K Bs/ sec. This is bettered by the ARINC 629 which operates at a speed of 2 Mbytes/sec and in real terms is 20 times faster than the ARINC 429. In addition the ARINC 629 can service 131 terminals on a data bus. ARINC 629 is used on the new Boeing 777 Aircraft. It uses a high-speed bi-directional bus capable of either regular or irregular transmissions. The MIL1553B is basically for military aircraft and the latest stealth fighters and bombers incorporate this technology. As safety measures for military and civil aircraft are different, the military standardization is MIL-STD, while for Civil it is ARINC.
ARINC is thus a very important part of the avionics bus system for transfer of information in a modern aircraft, military or civil