Fiber Optic Unit Promises More Crash Data

Joseph L. Tilton

Airplane crash investigations have been hindered by limited flight data, prompting the National Transportation Safety Board and the Federal Aviation Administration (FAA) to push for more recorded information so they can determine the causes of accidents. Raytheon Commercial Electronics has developed a fiber optic flight data acquisition and recording system that monitors 88 parameters, and it does so at a relatively low cost and weight.

The FAA has mandated that passenger aircraft built after mid-August 2000 must monitor and record 57 critical flight parameters (88 parameters by mid-August 2002). Some of today's flight recorders operate with as few as seven to 11 parameters. "Recent incidents like Swiss Air 111, which stopped recording five minutes before the crash, have heightened the call for better data and ultrareliable power systems," said Brian D. Morrison, director of Raytheon's Control-by-Light division. "Our system can continue operation even after a total loss of electrical power."

Typically, fiber optics has been expensive, with transceivers used in some aircraft architectures costing $5000 to $10,000 each. Raytheon's Distributed Flight Data Acquisition Unit lowers the incremental cost of fiber to less than $100 per transceiver. Each box, weighing about 2 lb, transmits data to a crash-survivable digital data recorder. The bidirectional optical units transmit and receive on the same cable, and form a ring connecting all boxes with one another while allowing each to work independently.

Off-the-shelf parts

Raytheon managed to bring the transceiver cost down so much through economies of scale, Morrison said, by designing a high-end transceiver that works with the same chips and optical parts as those in high-volume commercial applications. To meet high-reliability requirements, the company added features such as determinism and electromagnetic immunity where necessary.

Competing products generally evolve from military standards, he said. "Our experience has been that it's far more effective to grow a widely used commercial standard to meet aircraft safety and reliability requirements than it is to try and force-fit a military-derived product by pushing it down into commercial uses."

Morrison expects the units to be FAA-certified by December. Besides meeting agency standards, he anticipates other commercial uses for the technology, including ships and highway vehicles.