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Odd ATC Transmissions

Tue Aug 15, 2006 2:09 am

This is a random question but a few months back I was on a united flight, listening to channel 9, at phx, sitting in a long line, roughly 10-15 jets, waiting to take off. As I sat there and listened, the tower was clearing the jets for takeoff and then instructing the following jet to position and hold. However, what I found odd is that for roughly 4 or 5 of these exchanges after the jet was cleared to position and hold, it was instructed to acknowledge sight of the jet that was now rolling down the runway..something like "report company CRJ in sight"......then, after those 4 or 5, the rest of the position and hold instructions had no more need to acknowledge the plane in front on them in sight. It was a clear night, ceiling of maybe 9,000 feet and absolutely no fog or haze or anything.....any reason why this would happen and then they would just stop asking for that acknowledgement, or do they do this often...any ideas? thanks in advance
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RE: Odd ATC Transmissions

Tue Aug 15, 2006 2:23 am

It is an indication that the following aircraft will be given its takeoff clearance with regard to confirmation of sight the preceding aircraft. In visual flight conditions, ATC can allow more aircraft to take off if the following aircraft accepts responsibility for traffic separation from the preceding aircraft. It is not as haphazard as it sounds, as all aircraft are roughly the same speed, following roughly the same track.

This tactic is quite common at PHX, an airport geared for visual flight conditions, (for obvious reasons). Then look at the opposite .... under IFR conditions, see how traffic backs up for departure.
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RE: Odd ATC Transmissions

Tue Aug 15, 2006 2:24 am

As crazy as this might sound in order to apply visual separation between 2 aircraft the pilot must acknowledge sighting the other plane......so, thus the reason for the transmissions you heard, the controller had planned on using visual separation. Not often used like that on runways but it is the correct application.

Hope this helps.
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