NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The development of bubble sextants
From: Gary LaPook
Date: 2009 Aug 16, 01:51 +0200
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. 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 > > > > > > > --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---