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I know that TCAS are used to get 'Traffic Alerts' as well as 'Resolution Advisories'. But an RA seems to only provide instructions to avoid vertical collisions. How about the horizontal separation, how do we manage that ?

Ralph J
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Smile LiaZ
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2 Answers2

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A TCAS Resolution Advisory directs a vertical vector such as climbs and descents, but it is aware of both the horizontal and vertical position of other aircraft. After all, a collision is a collision, and the distinction between "horizontal collision" and "vertical collision" is a little artificial. TCAS uses vertical vectors to avoid any collision, whether or not there was any vertical component in the original collision-course vectors.

As far as systems that direct horizontal (ie heading) changes to avert a collision, that's ATC's role, and of course navigation systems to keep everybody "where you're supposed to be" will prevent all sorts of potential problems. But no on-board systems direct heading changes in response to another aircraft in the same way that TCAS does in the vertical dimension.

Ralph J
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To avoid colliding, two aircraft need horizontal separation or vertical separation, not both. If two aircraft are on a collision course, this means that their tracks and altitudes are converging. An RA will provide altitude separation. Their tracks will still cross but this is fine and normal.

Chris
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