Single point of failure?Apr 14, 2008
Yet I was concerned that no mention was made of the fact that this to-be-applauded approach to an integrated instrumentation display actually constitutes a single point failure mechanism — all the navigational eggs are now in one basket — and that, unless provision is made for a backup system, its failure could well jeopardize the well-being of vessel and crew.
A real-world example of such a situation occurred a few months ago on a well-found ketch on a passage down the West Coast to Mexico. In severe weather conditions, a boarding sea destroyed most of the cockpit instruments, including the integrated display. The skipper was an experienced and competent navigator, but weather conditions precluded the taking of star sights. It was only the availability of a hand-held GPS and radio that enabled an intercept to be made by a U.S. Coast Guard cutter for a tow of some 80 miles to the nearest harbor.
In recommending navigation systems to my clients, I stress the need for individual readouts of each sensor before consideration of any integrated display and then only its use as a “slave” instrument.
There is an analogy to this in current air transport design: glass cockpit-type displays provide a very comprehensive display of all critical data, but tucked into the corners of the instrument panel are individual instruments displaying the fundamental flight and navigation parameters essential to safe passage — just in case.
I don’t think it’s necessary for every data source to have an individual readout, provided the vessel’s position is always available on a hand-held unit or the equivalent.
The analogy to the design of modern aircraft instrumentation is useful, however. These days redundancy is most often (and always in commercial aircraft) achieved with the use of complete duplicate systems, with crossover and data swapping capability. The data available to the pilot in the event of a malfunction of a system is hardly diminished. But this is aviation where the cost of the glass panel in even a light aircraft can easily exceed $40,000.