Post by CoolP on Dec 7th, 2011 at 11:53am
Think of the transitions as a funnel-like segment to get all the planes on the actual STAR route being active. So no 'Monday we take this one, Tuesday the other one and at the weekends we fly direct' or something, but more or less a logical step concerning your route before the STAR. It won't be necessary all the time and it also won't be available at all airports.
The selection of the transition depends on your related position in regard to the desired STAR procedure.
Using the KORD arrival boeing247 was on, you could aim for PAITN where the actual STAR starts. Now when coming from the East, you may choose ASP as it offers a valid route to PAITN.
If ATC has cleared you for this, they know what you are doing in the lateral aspect of your route for the rest of your flight. That's vital as you may not have filed that segment, which can be long at some destinations.
Still the same STAR in mind, but coming from the North, you may choose TVC as it offers a northbound starting point for you.
Note the similar segment after PAITN for both directions.
As a matter of fact, all planes will later fit into the corridor the STAR describes, the transition segment just collects them. ATC then watches the separation, so not all of you will arrive at PAITN at the same time and/or altitude unless you are flying F-18 formations. :D
You will find your FMC being smart enough to 'connect the dots' if the desired route segments fits the current one. Otherwise it will give you a discontinuity and therefore ask for some more pilot input. Charts help or some programs do, as shown above.
If ATC clears you to a certain waypoint or even drops transitions, that's another beast. But your pilot made choice is based on that simple method. You look up the best fitting transition to get on the later procedure.
For SIDs, it's the other way through the funnel. All planes more or less depart in the same corridor and later transition to their planned enroute waypoints. The vectored segment then needs some interaction from ATC to turn you while keeping separation. So the 'uncommon' waypoint in the FMC is there for a reason as you will be in HDG select there and may later receive a direct-to.
The selection of the transition depends on your related position in regard to the desired STAR procedure.
Using the KORD arrival boeing247 was on, you could aim for PAITN where the actual STAR starts. Now when coming from the East, you may choose ASP as it offers a valid route to PAITN.
If ATC has cleared you for this, they know what you are doing in the lateral aspect of your route for the rest of your flight. That's vital as you may not have filed that segment, which can be long at some destinations.
Still the same STAR in mind, but coming from the North, you may choose TVC as it offers a northbound starting point for you.
Note the similar segment after PAITN for both directions.
As a matter of fact, all planes will later fit into the corridor the STAR describes, the transition segment just collects them. ATC then watches the separation, so not all of you will arrive at PAITN at the same time and/or altitude unless you are flying F-18 formations. :D
You will find your FMC being smart enough to 'connect the dots' if the desired route segments fits the current one. Otherwise it will give you a discontinuity and therefore ask for some more pilot input. Charts help or some programs do, as shown above.
If ATC clears you to a certain waypoint or even drops transitions, that's another beast. But your pilot made choice is based on that simple method. You look up the best fitting transition to get on the later procedure.
For SIDs, it's the other way through the funnel. All planes more or less depart in the same corridor and later transition to their planned enroute waypoints. The vectored segment then needs some interaction from ATC to turn you while keeping separation. So the 'uncommon' waypoint in the FMC is there for a reason as you will be in HDG select there and may later receive a direct-to.