Six years after the DATAC system was installed on the 737, the ATOPS program researchers began working on a joint project with the McDonnell Douglas Corporation that showed potential of someday usurping the ARINC 629 standard. The project was called the Optical Propulsion Management Interface System (OPMIS), and it represented a first step toward a concept called flybylight technology. Flybylight systems would use fiber optic cables instead of electrical wires to transmit signals to operate the flight and engine controls of an airplane.

Front view of NASA Langley's 737 Flying Laboratory.

Fiber optic technology had several potential advantages. The most significant one was that it could eliminate problems with electromagnetic interference (EMI) that often occurred with closely grouped electrical wires. Fiber optic cables could also carry much more information than electrical wires, so a flybylight system would have expanded capabilities. In addition, the technology was lighter weight than comparable electrical systems, which would translate into increased efficiency in aircraft performance.

McDonnell Douglas had been working on flybylight technology since 1987 and wanted to test the concept on an airplane. The McDonnell Douglas engineers decided to start with a fiber optic engine control system, because it would be a manageable project and it would be safer than experimenting with an entire flight control system. Even if a flybylight system failed, the test airplane would still have at least one good engine and all its flight controls functioning, so it could land safely.

The OPMIS project was actually a joint effort among several entities. McDonnell Douglas worked with United Technologies, Inc. to develop the basic flybylight technology. The big hurdle in the flybylight system, however, was the development of optical sensors to interface with the engine itself, and five different companies built experimental sensors to test during the research program. NASA engineers at Langley then integrated the OPMIS technology into the TSRV 737 airplane.

OPMIS used optical sensors installed in a bracket on the throttle controls to pick up any changes in throttle position. That change would be transmitted by fiber optic cable to the engine, where an engine controller would translate the optical signal to an electrical one which, through an actuator, would move the engine controls to correspond with the throttle position. Data on the operation of the OPMIS equipment would then be sent via fiber optic cables, but in the ARINC 629 data bus format, to the research pallets in the back of the 737 airplane. Although the point of the research was not to investigate data bus technology, the OPMIS research was the first time an optical ARINC 629 data bus had ever been flown on an airplane.

Developing the system presented some new technical challenges, because fiber optic cables had to be handled differently than electrical cables. Working with fiber optics required new techniques, as well as different connections, harnesses, and hardware. The NASA engineers also decided to incorporate shear fuses into the system that allowed the safety pilots to physically disconnect the OPMIS system from the engine in case of a problem or equipment failure. If the OPMIS equipment was disconnected, the engine control would revert to its baseline mechanical system.

Finally, in the spring of 1993, an operational OPMIS system was installed on one of the TSRV 737's two Pratt & Whitney JT8D7 engines. The research flights began in May 1993, and the researchers planned to fly OPMIS on the airplane on all its research flights. [Ref 6-7] Results would not be available for some time, but the TSRV 737 was continuing to play an important role in exploring the frontier boundaries of advanced aircraft systems.