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But there are three independent gyro instruments, the attitude indicator 
(AI) and the directional gyro (DG)driven by a vacuum pump on the engine 
and the turn coordinator (TC) driven by electrical power. This provides 
several levels of redundancy. If you lose the vacuum pump, you lose only 
the DG and the AI and if you lose electrical power you lose the TC. 
Pilots are taught to compare the three instruments against each other so 
as to identify a possibly faulty instrument or power source so we don't 
take the "black boxes" on faith.

 Other flight instruments are driven by sensing atmospheric pressure 
compared to ram pressure detected by the pitot tubes. The recent loss of 
an Air France flight over the Atlantic points to erroneous information 
from the pitot tubes, (but this might just be an attempt by Airbus to 
avoid responsibility for a weak tail structor, only time will tell) but 
there were several accidents in the '90s involving Boeing 757 aircraft 
in which tape over the static ports (for washing the aircraft) caused 
erroneous airspeed and altitude displays that the flight crew didn't 
cross check against the other flight instruments and resulted in the 
loss of the airplanes and all aboard. A well known incident involved an 
Airbus flying across the Atlantic. A fuel line broke to the right engine 
which allowed a lot of fuel to escape overboard. The flight crew noticed 
a fuel imbalance and pumped fuel from the good side of the aircraft over 
to the leaking side which eventually caused to plane to run out of fuel. 
After both engines quit after all the fuel had been pumped overboard the 
pilots were able to glide over one hundred nautical  miles and landed 
safely (only some damage to the plane itself) in the Azores. The pilot 
didn't believe that the fuel could be being lost as indicated by his 
fuel gauges and suspected that it was just a computer glitch.

gl

So modern pilots  may be relying too much on the black boxes and not 
doing the basic check of "does this make sense?" and doing the 
conservative thing of assuming the worst and taking action on  that 
assumption.

There have been some recent major crashes where the well trained airline 
pilots have forgotten this basic cross check.

gl



On Aug 15, 5:53 pm,  wrote:
 > Gary L, you wrote:
 >
 > "I have been a flight instructor for 37 years. We

frankreed@HistoricalAtlas.com wrote:
> 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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