The ATOPS program did not actually conduct any dedicated research into data bus design. But in 1983, the aerospace engineers who were responsible for the 737's research systems began looking for a better way to integrate the various system components. To make the experimental systems work, the flight control, navigation and display computers and any experimental equipment being tested on the airplane had to communicate with each other. Up until that point, each separate computer or component that needed to exchange information with any other system or equipment had to have a dedicated wire for each connection. In other words, if a computer had to give information to three other components and receive information from three others, it had to have a total of six cables connected to it. This limited the number of elements that could be integrated into the system, and made the installation of any experimental equipment a timeconsuming job.

David C. Holmes, who was chief engineer of the Experimental Flight Systems Section (EFSS), came across an experimental concept that he thought might be a great improvement to this cumbersome system. The new technology, called Digital Autonomous Terminal Access Communication (DATAC), was being developed at Boeing by an engineer named Hans Herzog. It was a design for a single, global data bus that would carry all the information between the different components of the airplane systems. The data bus consisted of a single twisted pair of wires, to which all the components that needed to exchange information were connected. Instead of mechanical splices, all the coupling was magnetic, and each "box" or computer needed only a single clip connection to the data bus. To keep the data from each component from getting jumbled with the other information being exchanged, each component's data was coded and "broadcast" in a synchronized order. All the information was transmitted on the data bus, and each computer or component could be programmed to pull off whatever information it needed. [Ref 6-2]

The DATAC system was a perfect design for the NASA 737. It would allow a far greater number of components to be integrated into the aircraft systems, and it would greatly reduce the amount of time required to add or exchange experimental equipment. Since the data bus had fewer wires and components, it would also be lighter and would require less maintenance than a conventional system. The only problem was that in 1983, DATAC existed in concept only. Herzog was working with it in a lab at Boeing, but the technology was far from fully developed. Nevertheless, Holmes presented the potential benefits of the system to William E. Howell, who was the chief of the Langley ATOPS program at that point, and Howell approved the idea. [Ref 6-3]

Putting experimental equipment on the TSRV airplane was nothing new. But this case was different. The data bus was part of the airplane's basic infrastructure. If it did not work, none of the experimental systems, including the navigation, flight control and display computers, would be able to function. In addition, there was a time element to be considered. The 737 was expected to be grounded for the upgrade and an engine repair for about a year. But that was not very much time to develop the technology for a new data bus, build aircraftcompatible equipment, design whatever software it needed to operate and install it in the airplane. If the airplane was ready and the data bus was not, it would set all the ATOPS research projects behind schedule. Yet the potential benefits seemed worth the risks involved.

The development of the DATAC data bus became a joint effort between Boeing and NASA. Herzog and his team designed and built the data bus itself and the terminals that provided the interface between the data bus and the computers or components using the system. NASA engineers designed interface boxes and software that would convert the data from the format needed for transmission on the data bus to a format the 737's computers and experimental systems could understand.

Boeing first had to create crude laboratory versions of the terminals to send to the Langley Research Center so the engineers there could begin developing the software. The Boeing researchers then worked on designing aircraft versions of the terminals, which had to be smaller by two thirds than the laboratory equipment. In the summer of 1984, after a yearlong effort, the data bus, the magnetic couplers and the aircraft versions of the terminals were ready. Herzog and several of his coworkers travelled to Langley with the equipment to help integrate it with the NASAdesigned interface boxes and software and install the system in the airplane.

The equipment still needed a fair amount of finetuning, however, and time was getting short. The rest of the upgrade was nearly finished, and the 737 was scheduled to begin flight testing again in a few weeks. As a result, the BoeingNASA crew spent many long hours in Langley's Experimental Avionics Simulation and Integration Laboratory (EASILY) working out bugs in the system, including one memorable weekend when the power went out in the building. Time was too precious to wait until maintenance crews could fix the problem Monday morning, so the crew set up a generator in the parking lot and continued working with flashlights and small work lights throughout the weekend. [Ref 6-4]

By the beginning of August 1984, DATAC was installed and working in the airplane. The 737 made an excellent test bed for a new data bus, because the equipment in the front cockpit remained conventional. If the DATAC system had ever developed a problem in flight, the safety pilots could have taken over and flown the airplane. The system never had any such problems, however. The Langley engineers and technicians were extremely pleased with its operation and reliability, as well as the ease with which new experiments or systems could now be integrated into the airplane.

In September 1985, after the DATAC system had flown on the 737 for over a year, a team of engineers working on Boeing's new transport design, designated the "7J7," visited Langley to look at some of the new technologies the ATOPS program was exploring. Howell was giving them a demonstration of the equipment on the TSRV airplane, when one of the engineers asked if DATAC was being used for data recording. Howell told him it was being used not only for data recording, but for the full experimental flight control system. The Boeing engineers became more interested, and asked how many problems the NASA crew was experiencing with the data bus. "None," Howell replied. In that one simple interchange, a significant amount of the NASA work on DATAC was successfully transferred to industry. [Ref 6-5]

Boeing actually owned the DATAC technology. But the system might not have been developed enough to use in the 7J7 design had NASA not supported Herzog's work. By the same token, the design team working on the 7J7 might not have had the confidence to use a dramatically new technology for something as important as the basic system architecture of a new airliner if it had not proven itself first on the TSRV airplane. Although the 7J7 was never built, the DATAC technology was incorporated into Boeing's next jet transport design, the B777.

DATAC worked so well, in fact, that Aeronautical Radio, Inc. (ARINC) used it as the basis of a new industry data bus standard. ARINC is a notforprofit organization owned and supported by the airlines that sets standard specifications for technology, so the products developed by different manufacturers will be compatible with all commercial transport aircraft. The specification for the new data bus, called ARINC 629, was adopted in September1989. [Ref 6-6]

The DATAC research was a somewhat unusual joint partnership between Boeing and NASA. The bulk of the development work was done by a Boeing engineer, and the work was supported by NASA primarily because the data bus could give NASA's own B737 test airplane enhanced capability. In the process, however, the TSRV 737 played a crucial role in gaining acceptance for the data bus in not only Boeing's newest airliner, but the entire next generation of transport airplanes.