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    Re: The development of bubble sextants
    From: Gary LaPook
    Date: 2009 Aug 16, 01:51 +0200

    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
    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 
    > 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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