At 06:32 PM 21/06/05 -0500, you wrote:
>Why are we getting so focused on 200'?
Because people asked the question "how close is too close?" and I pointed
out what is apparently a little known "rule".
200 feet at least provides a guide - you want to miss the other guy by at
least that much. Of course popping up in front of or crossing 200 feet in
front as you enter will upset someone. I've always taken the 200 feet as
the desired minimum when established in a thermal. I know someone who had
two mid airs(both were just touches) which might have been avoided by more
sensible seperation. You want more seperation when relative speeds are high
How many glider midair collisions
>have there been from people misjudging how close they were?
See above and a few more at least I can think of in Oz in the last 15
years. Plus the near misses. And see below.
I would imagine
>that in most midair collisions, at least one pilot didn't see the other
>aircraft, therefore being at least 200' away from the other glider was a
>moot point.
???. If at least one pilot saw the other and a collision or near collision
developing he is required to take evasive action - no matter who had "right
of way" or thought he did.
Even from the perspective of the pilot who could see the
>approaching glider, waiting until 200' to initiate avoiding action could be
>too late.
Please spare us, who would do that if they saw a close call/collision was
imminent?
You take evasive action as soon as you see that the other guy is going to
come within 200 feet of you. He might be half a kilometer away at the time.
Increase that distance for certain rego's. You'll learn them quickly.
>
>I believe that lookout and recognition of collision potential are far more
>important.
So if you see someone coming a miss distance of 50 feet is OK? Knowing what
you want the miss margin to be is important.
Again 200 feet is a good guide to a reasonable MINIMUM.
If you are going to hit another aircraft, it will be stationary
>in the canopy - you won't hit another aircraft if the relative line of sight
>is moving. Therefore if you see an aircraft that is stationary in the
>windscreen at any distance you need to initiate avoiding action.
Absolutely and dangerously WRONG. What you describe is a special case where
both aircraft are flying in straight lines at constant speed.(mostly true
for power planes) There are other cases like being in formation (in a
thermal or not) where this is also true. It is NOT TRUE more generally when
at least one aircraft is accelerating. Circling is acceleration into the
center of the circle.
I encourage everyone to draw this:
If you approach a thermal at a tangent such that you and a glider in it
will arrive at the tangent point simultaneously, the glider in the thermal
has never been stationary in your field of view nor you in his, yet you
collide! I've never seen this described in any gliding publication. This
appears to be what happened in one fatal mid air in Oz.
See Chip Garner's description of the collision between his LS4 and a Navy
A7 about 12 years ago in California. The jet was on a curved flight path
and Chip didn't think a collision was developing until it happened. The LS4
lost 4 feet of one wingtip and the A7 recovered to base but the engine
didn't like the aileron hinges.
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
phone Int'l + 61 746 355784
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Int'l + 61 429 355784
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