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Gary L, you wrote:
"I have been a flight instructor for 37 years. We demonstrate to all student 
pilots that they can't use their natural balance sense to determine which way 
is "up" while in flight. We demonstrate this by having the student close his 
eyes and then we maneuver the aircraft and ask the student to tell us what 
the airplane is doing. We then tell them to open their eyes and they are then 
surprised that they were completely wrong in their estimate based on their 
semi-circular canal senses."

And this reveals a fascinating cultural difference between traditional 
mariners and traditional aviators. From the earliest lessons, aviators are 
taught that the instruments, the "black box" instruments (!), can be trusted 
while the "mark one accelerometers" in our heads cannot be trusted at all. By 
contrast, as we've seen in a number of posts in the past few months on 
NavList, many mariners believe that the "black box" instruments should be 
treated with suspicion while the "mark one eyeball" is always your friend. 

For mariners, in today's increasingly electronic navigational world, I have a 
feeling that the experience of aviators is going to become more relevant. The 
electronic navigational tools work 99.99% of the time. What's required is not 
more "mark one human sensor" instrumentation, but rather the error-detection 
skills, which depend heavily on the last redoubt of the skilled navigator -- 
the human brain itself, that let us identify those rare circumstances when 
either the electronics or the biological sensors are giving us incorrect 
information. The key is knowing that there is something wrong. And if you can 
detect an instrument problem, you can switch to backups. 

This all leads to the subtle problem of false alarms. Reading more on the 
grounding of USS Port Royal, it appears that the "Voyage Management System" 
aboard these vessels is notorious for frequent alarms. When the VMS warned 
them that the inertial system and the GPS did not agree, the navigators that 
day did what experience had taught them to do: they ignored the alarm. It's a 
case where the vessel had thee complete, highly accurate systems which could 
almost instantly read out position: GPS, radar, and inertial (while there 
were no radar repeaters on the bridge, the radar was active and functioning). 
Unfortunately, the crew for some reason (random bad luck? poor training? 
deliberate sabotage of a commander they disliked?) chose to trust the one 
system that wasn't working that day. They didn't have, or didn't use, the 
skills that would have allowed them to detect the failure of one of their 
navigational systems.

-FER



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