Airborne_Again wrote:
Is the instruction to leave on a radial or on a heading?
Sorry, I wasn’t awake. Good question. The instruction is always to leave on a radial. I have have never heard an instruction to leave a waypoint on a specified heading.
Generally when you get that instruction it is a relatively small turn and it makes no odds, but if it were a big turn and you flew over you would be significantly displaced. I think that the reason you leave on a heading, not a radial or track, is because it marks the start of radar vectoring as opposed to own navigation and tighter separation can be applied.
huv wrote:
We get that kind of ATC instruction all the time here at EKRK since the arrival routes have no name and begins at one of two different VORs.
Is the instruction to leave on a radial or on a heading? If instructed to leave on a radial, then fly-by would certainly make sense. If instructed to leave on a heading, I would fly over.
RobertL18C wrote:
However if ATC say leave WPT x on heading 230 degrees it would be treated as as fly over.
We get that kind of ATC instruction all the time here at EKRK since the arrival routes have no name and begins at one of two different VORs.
I have always performed turn anticipation just like I would when passing any other en-route waypoint.
Although they probably exist, I have never seen a fly-over waypoint on an en-route or arrival chart.
I would think that in most GA scenarios the speed is so low that it makes no practical difference whether a waypoint is fly-by or fly-over. Maybe a fraction of a mile…
The time it makes a big difference is when you are turning through a huge angle, say 300 degrees, but in IAP the max angle is roughly 90 degrees.
Or if there is a lot of wind; then you need to do a complex computation, and there may not be a solution within the constraints of a Rate 1 turn, or some equivalent roll angle. Then this is relevant…
Timothy wrote:
Treated by whom? I think that if I had that instruction, I would treat it as fly-by, or you would be displaced from the line they were expecting.
I always treat that instruction as fly over. In the UK it is usually “depart OX on heading of 360”. If it isn’t, when do you commence the turn?
RobertL18C wrote:
However if ATC say leave WPT x on heading 230 degrees it would be treated as as fly over.
Treated by whom? I think that if I had that instruction, I would treat it as fly-by, or you would be displaced from the line they were expecting.
It depends on ATC sometimes.
So leaving an airway the end point is typically a fly by and the GPS will treat it as such.
However if ATC say leave WPT x on heading 230 degrees it would be treated as as fly over.
AeroPlus wrote:
With some autopilots such as the STEC55, you have to press the NAV button twice (display will show GPSS) for the AP to anticipate the fly-by waypoints.
If you mean, how to engage GPSS/Roll Steering, there are many different ways:
Button on panel
On Gx00 hold down HDG button
On Aspen press GPSS button
etc.
That is a rather different matter from Balliol’s question (which has also exercised me for my PBN teaching.)
With some autopilots such as the STEC55, you have to press the NAV button twice (display will show GPSS) for the AP to anticipate the fly-by waypoints.
