FMC Discontinuity - do I have to fix this or wait until I receive vectors?

I had a recent flight into YSSY. Star: Boree3A Rwy: 16L
The last point of the Star is OVILS. The IAF for the ILS is TONUX (about 1 NM apart.
The 737-800 FMC shows

OVILS
158deg track
(Vector)
183deg 1.0NM
TONUX

The Vector is a Discon. My question is do I solve that pre or in-flight, or do I wait for an ATC vector that may or may not come. It leaves LNAV/VNAV unprescribed and a further problem with this approach is possible conflict with Rwy16R, if no path or HDG is selected.

So what should I do? thanks anyone

IRL you would leave the disco in the plan and SYD Approach would tell you what to do, could be a vector, could be tracking direct TONUX. In the sim I’d probably delete the disco so you get a bit of a turn to TONUX for the approach, or go direct TONUX sometime before you get to OVILS.

As for the conflict with 16R, there’s a blurb about parallel runway operations at Sydney, a prominent point is that you must not fly through the centreline of your assigned runway, even if Approach haven’t cleared you to intercept final yet. So if you’ve been assigned 16L and you’re on a heading that takes you through the centreline, arm LOC so it captures the Localiser. Once Approach clear you for the approach you can arm the glideslope.

If Sydney Approach want you to fly through the centreline, they will specifically tell you that. Obviously this wouldn’t be simulated by the SIM ATC, so you just have to do your own thing to simulate those rules yourself.

For exactly this reason I remove all discontinuities before departure… However others may take a different approach.

In terms of receiving vectors from ATC, I tend not to rely on this actually happening during the approach. Generally in game ATC tends to allocate some sort of arrival procedure and then waits until the aircraft is somewhere close to where ATC thinks the aircraft should be before transferring to the tower frequency. (ATC has also been known to issue bizarre altitude instructions during an arrival procedure, sometimes involving a climb to an unrealistic altitude. I find it best to ignore such instructions and continue to follow VNAV and ATC usually sorts itself out and transfers me to the tower when getting close to the final approach track. Another useful tip is maybe to select your own approach from the ATC option window when allocated an approach, usually selecting an ILS approach without a procedure allows for “self positioning”, i.e. follow the STAR and approach plate as planned.)

As DashQuickly said in the post above, in real life this discontinuity would be left in the FMC and ATC will offer instructions at the appropriate point as to what to do. In MSFS it is the pilot who will have to take the initiative on this one and make up their own mind as how to procede. Removing the discontinuity prior to departure allows for a fully prepared flight path in the FMC to runway threshold and prevents the aircraft flying away from the airfield on autopilot.

excellent response thanks. I’ll follow that.

yes agree with your notes too. Thanks so much. I should have mentioned I’m flying with Vatsim so instruction is clear and unambiguous. Great thanks

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Yes, if flying on VATSIM do not clear the discontinuities, unless you enjoy being corrected by the controllers :slight_smile:

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true, but then I ended up in ‘no man’s land’ without VNav/Lnav engaged and no heading…so at least with the discon’s gone, the FMC will follow some path until changed…I think I agree with the above. I don’t mind over-riding with HDG select at any time as a controller wants

You aren’t “overriding” exactly, you are flying the flight plan. There is a disconnect between the Departure and your en route course, or the course and your arrival.

The charts (SID’s/STAR’s) will tell you what headings to fly and the altitudes along with “unless instructed by ATC”.

So if you aren’t using VATSIM, or Pilot2ATC, Etc… then yes, fly the SID / STAR as per the chart and then you can vector yourself (heading) to intercept your course. And in that instance, you could also just clear it and have a complete track, that is up to you :slight_smile:

If you are on VATSIM, the controller will give you a heading to fly when they are ready, or tell you “direct on course” meaning you can fly to whichever waypoint directly and then continue your filed flight plan.

I hope that makes sense :slight_smile:

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Well in the Sydney example you should be tracking 158º from OVILS, so you leave the disco in and then either let the FMC provide the 158º track, which it looks like the 737 is doing for you, or adjust heading to maintain the 158º track.

It’s only a 1NM gap to turn 158, so if selecting HDG manually, it’s pretty tight of course. But wouldn’t removing the discont, ‘automatically’ do this anyway? i.e. LNav will turn as it links the two waypoints?

The STAR is to hit OVILS then track 158º and wait for vectors, you ignore TONUX unless told to go there. The fact there’s only a mile between them is irrelevant because TONUX is not part of the procedure. If you remove the disco then it will track to TONUX and that is not correct. IRL you would be getting vectors or other instructions before reaching OVILS but I don’t know how the VATSIM guys are handling it. Either way, tracking 158º from OVILS is all you are authorised to do until given further instructions.

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OK. that’s clear and I see where you’re going with that. True - you don’t have clearance to track differently.

The reason why discontinuities and vectors exist is because IRL the sky is filled with aircraft coming and going. ATC uses STARs to funnel traffic to the approaches/runways in use. ATC and the FAA in the US do their best to keep airliner traffic moving smoothly to meet their schedules. The are times when too many aircraft want to land at 5:00 PM when there are two active runways. ATC has tools to accommodate large amounts of traffic. One tool ate holding patterns. Another tool is discontinuities and vectors. ATC uses that break in the flight plan to turn aircraft in different directions to delay them a few minutes. Other times like 2:00 AM there isn’t much traffic. If weather conditions are good, ATC can give vectors to the runway to speed things up by not having to fly the complete ILS or RNAV approach.

In MSFS, using real-time traffic, MSFS ATC can’t issue vectors to real aircraft to sequence you correctly onto the approach. But MSFS ATC isn’t sophisticated enough to sequence all aircraft correctly. If using MSFS ATC it is okay to remove discontinuities. Other 3rd party ATCs probably manage traffic differently and need the discontinuities left in the FMS.

Yes thanks…I only use Vatsim, so a degree more of realism in flying of course. It seems there are mixed forms of advice re this event, so I’ll go by Vatsim’s rules…I appreciate all the comments made.

Do not delete the discontinuities. They are there for a reason.
All of the people who are telling you to delete them so that the FMC computes a path to the final are 1000% incorrect. This action is exactly what the procedure does not want you to do, hence why the discontinuity exists. The procedure wants you to continue flying on a heading or some other indefinite course until you are turned back in by ATC.

If you’re not operating with ATC, then you can simulate this action by flying your heading and then turning yourself back in at some point. Don’t let the FMS create a path without the discontinuity.

yes. thanks. As someone else said, the STAR is a clearance - the FMC is a tool…a good thought!