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Old August 19th 03, 06:17 AM
Chip Jones
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"blanche cohen" wrote in message
...
Um....Bob & Chip...could you explain in more detail the reason
for the "turn into traffic"? I'm having problems visualizing
it. And I have the most horrible feeling that someday I'll run
in the same problem and want to understand it.


To keep it simple, imagine two aircraft converging at 90 degree right
angles. One is heading northbound, one is heading east bound, on collision
courses. Assuming a vertical solution is not a viable option, the fastest
way to achieve separation is to turn one aircraft decisively behind another
aircraft. This kind of turn involves the nose of one aircraft swinging
through the vector (ie- the projected path) of the other aircraft. This
requires a turn towards the other guy. The closer the two aircraft are to
one another when the maneuver is initiated, or the narrower the angle of
convergence, the more of a turn is required. Aircraft types, winds aloft,
other traffic in the scenario etc all play a factor in who gets turned and
how much of a turn is needed. Generally, if all things are considered
equal, one turns the slower aircraft behind the faster aircraft.

This kind of turn can be be counter intuitive to the pilots involved. In
the case of the aircraft heading 090 and the aircraft heading 360, let's
suppose that I issue traffic traffic and then initiate an separation
resolution. To the north bound aircraft, I call traffic at ten o'clock and
ten miles, eastbound co-altitude. I then initiate a vector to put the north
bound airplane behind the east bound airplane. "Turn left heading 310,
vectors behind traffic." To the pilot, I have just issued a turn right into
the traffic I just called. In the controllers mind, I have taken other
factors into play. The east bound aircraft has a tailwind, so the 310
vector will aim the northbound guy into the wind, slowing him down. The
northbound guy was slower anyway. There is more traffic to the south,
precluding a southerly turn to the eastbound aircraft etc etc etc. The
pilot may say "Say again Atlanta? Isn't that where my traffic is?"

The very very basic idea is that assuming I have enough time to aim the nose
of one airplane at the point in space that the other airplane occupies when
I inititate the maneuver, then by the time his nose actually gets there, the
other aircraft has moved on. This assures that neither aircraft will hit
(assuming they don't get together in the turn.) Lots of variables too.

Chip, ZTL





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