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    Re: The development of bubble sextants
    From: Gary LaPook
    Date: 2009 Aug 15, 16:47 -0700

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