NavList:

   

Reply

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 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
--~--~---------~--~----~------------~-------~--~----~
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply