By John McHale
Historically the commercial avionics designers have preferred Arinc 429 and other databus protocols for their systems, but databus manufacturers say they are seeing growing interest in MIL-STD 1553 for use in commercial aircraft cockpits.
"We're seeing 1553 getting a lot of interest right now from the commercial aircraft industry," says Mike Hegarty, principal marketing engineer at Data Device Corp. (DDC) in Bohemia, N.Y. Traditionally 1553 was not used in flight critical systems on commercial aircraft but now system integrators are finding it meets their needs in newer systems such as the Airbus A350 XWB, he adds.
Airbus and companies like them are "very risk adverse" and do not want to invest in a technology that may hurt them safety wise down the road, Hegarty says.
The architecture of safety critical systems, such as flight control systems, in new aircraft is moving from centralized processing toward distributed processing in which a redundant array of processors are used to control intelligent actuators over a digital communication bus, Hegarty says. "MIL-STD-1553 is an ideal choice for the databus between the processors and actuators because of its robust performance and deterministic protocol."
They like 1553 because it is a recognizable standard, rugged, and reliable, which also translates to a lower cost of ownership over the life of the product, he continues. Also, 1553 has a track record of more than 30 years of in service history which is invaluable when it comes to safety certification to Federal Aviation Administration (FAA) standards such as DO-254 and DO-178B, he adds.
"I find it curious," says Bill Schuh, vice president of sales at Ballard Technology in Everett, Wash. The commercial aircraft industry "spent all this money on developing AFDX and now they are coming back to 1553."
It tells you a lot about 1553 and what the technology can do and how reliable it is, Schuh says. It may not have the high-speeds of other databus protocols, but many applications do not need that kind of throughput and avionics designers find that for systems that only need the 1 megabit per second performance, nothing is better than 1553, he adds.
"We see 1553 in a number of application cases other than military test, simulation, and embedded," says Ben Daniel, business manager for avionics at GE Intelligent Platforms in Santa Barbara, Calif. "One of these is a recently publicized civilian aircraft and we have been involved in the development, test, and simulation there for quite a while. There are other applications as well that come up which at first may seem surprising but in fact are based on fundamental benefits that 1553 offers."
Daniel also says the market is starting to pick up.
"We still see some commercial reserve regarding speculative investment by many, but at the same time our customers are increasing dialog regarding what can be done for upcoming demand," he says. "They are looking to us to continue technical, price, and product availability responsiveness and we have received numerous plaudits for maintaining that attention to them even in today’s somewhat more subdued operational tempo."
During the last decade there have been various efforts to improve the speed of the venerable 1553 databus. While actual products have yet to be developed and fielded in deployed systems, the efforts continue.
Hegarty says DDC is still developing 1553 technology and has demonstrated it flying on a F-15 fighter. The next phase will be to turn it into a product which will require a program and specific requirements such as form factor, etc., he adds.
"We're optimistic that it will move forward," Hegarty says. It will function with speeds between 50 and 100 megabits per second, depending on the system, he adds
GE has "business in 10 megabits per second 1553, which swells and ebbs with particular specific program phases," Daniel says. "There is some reinvigorated activity recently which we are supporting."
Other databus trends
"We see continuing migration into new host platforms, including Windows flavored operating systems and PCIe backplanes," Daniel says. "We see PCMCIA slowing down (not surprisingly) and ExpressCard increasing. ARINC 664 is also paying off in adoption by the developing market new airframe projects."
GE has released AMC, XMC, and PCIe for 1553, he continues. "We’ll release PCIe for Arinc 429 next. Along the way we're adding features to both Arinc 429 and 1553 functionality to give the test and simulation customers more tools to work with."
Many of Ballard's commercial avionics users still go with Aring 429 products, Schuh says. Ballard's latest is a member of their AB-2000 family and it is called the AB2- AID Box and is already used by Cathay Pacific for an interface between and electronic flight bag and the aircraft's regular avionics, he adds.
Another trend Hegarty says he is seeing is the adoption of technology from the automotive industry for use in commercial aircraft.
Components used in the car industry such as CANBUS are low-cost because the industry's very high volume, but there have always been reliability and ruggedization issues when transitioning the technology to commercial aircraft.
DDC is working within a Society of Automotive Engineers (SAE) standards development process to use automotive databus protocols on the 1553 physical layer -- transceivers, Hegarty says. The engineering behind it is based on TTTech's Time Triggered Protocol (TTP) technology, he adds. TTTech is leading the SAE effort.
The product DDC is developing today runs at 4 megabits per second, Hegarty notes.
GE also has a relationship with TTTech, and is "successfully serving demand for TTEthernet and TTP product into various market areas," Daniel says. "We are paying close attention to where the customers want to go with these and intend to be there for them for the emerging time triggered protocols. To date it is not clear that TTP adoption would be accelerated by changing the physical layer."