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Thread: Saftey - the high risk of a mid-air collision - 8/10/2019

  1. #1
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    Saftey - the high risk of a mid-air collision - 8/10/2019

    There is an extremely high risk of a mid-air collision at choke points along the Mendos.

    Due to the terrain, the lines of lift often run in narrow corridors along mountain ridges. Back in the early 1990's, Robert "Bob" Seamans developed and published a procedure for the White-Inyo Mountain range on the east side of the Owens Valley. See a PDF of that procedure here:
    http://www.pacificsoaring.org/docume...re-alpha-c.pdf That procedure comes to mind when I fly from Williams.

    I believe flights along the Mendos present an even greater risk than did the Whites. Two common choke points worth mentioning, especially for tomorrow's flights (Saturday, 8/10 2019) are:

    • From St John turnpoint (TP) to Alder Springs TP
    • From Yolla Peak TP to and past the T-15 TP


    The forecast for tomorrow indicates the lift will be in an especially narrow corridor. The corridors between those points are the strongest lines of lift, the highest potential for clouds, and the width of those corridors are approximately between two and three miles wide.

    If you are flying on the Mendocino Mountains (the Mendos) and you know there are other gliders flying also flying from Williams on that same day, then you should religiously broadcast your position while on high speed runs traveling along the Mendos. I use the format of "Call sign, location (the prominent TP that I am near), Altitude (rounded to nearest 500 ft), and direction of flight.

    Example - "Glider 88, St John, 10,000 ft, northbound"

    very short! very informative!

    A couple of obvious statements:
    • gliders coming directly at each other on a collision course are EXTREMELY difficult to see (even on a clear day)
    • most gliders are equipped with FLARM (anti-collision device)
    • FLARM is not totally reliable due to:
    • There are blind spots that FLARM does not see
    • FLARM sometimes malfunctions
    • you may not always hear the warning (especially cruising at high speed, loud radio, loud vario)
    • you may not always see the warning (sun glare on the display screen)


    • (some) glider pilots often violate the FAA Rules of cloud clearances
    • even if both pilots are in compliance with cloud clearance Rules, you still may not see the other glider due to camouflage effect ( a white glider with a white cloud background)


    Flying at an altitude of 11,000 feet, with an indicated airspeed of 70 knots (80 MPH), then adding 10 MPH for correction of air density makes it a speed of 90 MPH for each ship, thus the collision speed is double 90, which is 180 MPH, or a nominal closure speed between the two ships of 264 feet per second ( and you will require about 5 seconds to avoid the crash (1 to interpret what you see, 1 second to decide your action, 3 seconds to alter your flight path or a total of 5 seconds (264 x 5 = 1320) - a quarter of a mile before the crash)).

    If you are the pilot in one of the two ships that are on a collision course, each traveling towards each other at 90 MPH, then...
    - you have 60 seconds before the crash, when still 3 miles apart
    - you have 20 seconds before the crash, when still 1 mile apart
    - you have 10 seconds before the crash, when still a half mile apart
    - 5 seconds before the crash, it's a done deal...


    Fly safely
    Peter Kelly

  2. #2
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    Re: Saftey - the high risk of a mid-air collision - 8/10/2019

    Excellent points! The risk seems remote until it happens to you. I will announce positions.

  3. #3
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    Re: Saftey - the high risk of a mid-air collision - 8/10/2019

    RASP for tomorrow has been updated.
    I have captured and abbreviated the convergence line display.

    The three mile wide corridor that most pilots will be flying from St John, to Alder, to Yolla, to T-15 is now more narrow than ever. Cloud base will be less than 10,000 ft along most of that corridor, and high speed travel will be easy to do. Be careful out there.

    Click image for larger version. 

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    Peter Kelly

  4. #4
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    Re: Saftey - the high risk of a mid-air collision - 8/10/2019

    Thanks Peter for the reminder about the high risk of collision. Of course there is nothing more effective than functional powerflarm to avoid mid airs.
    On many days we have a narrow area to fly as Peter described, although today is not a good example. The forecast for today is for clouds anywhere from the coast to the Sierras, so a perfect day to fly elsewhere. There is no need to stick to a narrow convergence line like in many other days. Fly the valley, or across the valley, there is no need to congregate along the crest where the working band will be much smaller than further away.
    My glider is at Truckee so I am not flying today. I will be visiting clearlake so come fly over my head and make me jealous.

    Ramy

  5. #5
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    Re: Saftey - the high risk of a mid-air collision - 8/10/2019

    Key and Ramy,

    Thanks for adding emphasis to this threat to our safe flying. We all just need to remind ourselves of these hazards, and do what we can to mitigate the threat.

    Yes, the fcst has fizzled out, so today is not a good practical example, but there are many days when the actual fcst does evolve as I had described and as it was programmed to do, based on last nights RASP.
    Peter Kelly

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