Thompson Arrivals and Departures
Moderators: sky's the limit, sepia, Sulako, North Shore
-
groundtoflightdeck
- Rank 6
- Posts: 416
- Joined: Sun Feb 15, 2004 9:56 pm
Thompson Arrivals and Departures
How come the radar is such that aircraft can get vectors in YTH, but you cannot have an aircraft on approach to one runway and another depart?
Alright, I'm not a Winnipeg North Low controller, nor am I familliar with the in's and out's of how they do things at YTH, but here's a stab at the reasoning based on my limited knowledge. Anyone feel free to correct me.
First of all, the aircraft departing must be airborne 3 minutes before the arriving aircraft reaches the runway, and the arriving aircraft must be clear of the departure path before the clearance can be issued. This leaves a pretty limited window to get a clearance and get into the air if the arriving aircraft is doing anything other then a strait-in approach. The other problem comes in trying to figure out what the clearance cancelled time is, based on the 3 minute rule. How do you know at what time an aircraft is going to be 3 minutes from the end of the runway? Do you use the aircraft's estimate for the navaid, which is going to add quite a bit of time, since the aircraft is going to slow down and manuever for the approach? Do you use his estimate for the navaid, plus 8 minutes for a standard procedure turn? What if the aircraft doesn't do a standard turn and only takes 6 minutes? Or 2 minutes?
This by itself isn't a huge deal, but the bigger problem is that the North Low controller who's working the traffic in and out of YTH is also working all the traffic into and out of YYQ, YNE, YIV, and about a hundred other small towns, as well as working all the en-route aircraft just passing through the airspace. They just don't have the time to vector everyone and work out arrival vs. departure separation with exact clearance cancelled times for everyone going into or out of YTH right down to the minute. They are not terminal controllers, working with a tower.
In a tower/terminal environment, much tighter arrival vs. departure separation can be used, as the tower has positive control over when aircraft enter the runway, and when they are permitted to take off. As such that 3 minute requirement can be shaved down to as little as 2 miles, and since the tower controller is looking at a radar screen, as well as looking out the window, he can (being a controller himself) monitor the aircraft on final and issue takeoff clearances or hold short instructions as per the situation, as well as issue go-around instructions to the aircraft on approach if the departure doesn't get airborne quick enough. Something that is not at all possible with FSS at YTH.
First of all, the aircraft departing must be airborne 3 minutes before the arriving aircraft reaches the runway, and the arriving aircraft must be clear of the departure path before the clearance can be issued. This leaves a pretty limited window to get a clearance and get into the air if the arriving aircraft is doing anything other then a strait-in approach. The other problem comes in trying to figure out what the clearance cancelled time is, based on the 3 minute rule. How do you know at what time an aircraft is going to be 3 minutes from the end of the runway? Do you use the aircraft's estimate for the navaid, which is going to add quite a bit of time, since the aircraft is going to slow down and manuever for the approach? Do you use his estimate for the navaid, plus 8 minutes for a standard procedure turn? What if the aircraft doesn't do a standard turn and only takes 6 minutes? Or 2 minutes?
This by itself isn't a huge deal, but the bigger problem is that the North Low controller who's working the traffic in and out of YTH is also working all the traffic into and out of YYQ, YNE, YIV, and about a hundred other small towns, as well as working all the en-route aircraft just passing through the airspace. They just don't have the time to vector everyone and work out arrival vs. departure separation with exact clearance cancelled times for everyone going into or out of YTH right down to the minute. They are not terminal controllers, working with a tower.
In a tower/terminal environment, much tighter arrival vs. departure separation can be used, as the tower has positive control over when aircraft enter the runway, and when they are permitted to take off. As such that 3 minute requirement can be shaved down to as little as 2 miles, and since the tower controller is looking at a radar screen, as well as looking out the window, he can (being a controller himself) monitor the aircraft on final and issue takeoff clearances or hold short instructions as per the situation, as well as issue go-around instructions to the aircraft on approach if the departure doesn't get airborne quick enough. Something that is not at all possible with FSS at YTH.
-
groundtoflightdeck
- Rank 6
- Posts: 416
- Joined: Sun Feb 15, 2004 9:56 pm
Actually, we used to be able to do exactly that. The departing aircraft would be given "Do not depart until ABC123 reports the fix outbound, clearance cancelled when ABC123 reports the fix inbound."
This worked quite well, until there were a couple incidents in which the arriving aircraft was "too busy" (read forgot) to report the fix and proceeded to break cloud and find his traffic still on the runway. That separation standard was quickly taken away, and now we can only use it when we have a tower.
This worked quite well, until there were a couple incidents in which the arriving aircraft was "too busy" (read forgot) to report the fix and proceeded to break cloud and find his traffic still on the runway. That separation standard was quickly taken away, and now we can only use it when we have a tower.
