Question about RNAV

[caucatc]

I have just got a question about RNAV , we were told that if controller vector aircraft leave the RNAV ,we should tell pilot direct to a fix when we want aircraft back to the procedure rather than a heading,like "XXX,direct to AA111 ,join DOGAR7A" ,but I asked a pilot if he can join the procedure if I just give him a heading not a fix ,the answer was affirm and he really did it ,the point he intercept the procedure is not any fix of the procedure ,can anybody tell me why can not use a heading to intercept the procedure ?

[Tipo83]

I am unsure but it might be to ensure correct waypoint sequencing. If you clear a pilot to intercept via a heading there is more work involved to ensure the FMS/GPS is positioned in the correct part of the flight plan so as the waypoints will sequence properly.

[Stoffel_KT]

I'm not exactly sure if what I'm gonna say is the what you are asking about since I'm talking about upper airspace and I think you might be talking about approach if I'm not mistaking.... But I guess this should be about the same.

When we vectored an acft we always had to make it resume it's own navigation direct to a point. If we wouldn't do this you don't officialy know what the acft will be doing. Normally it should be resuming his filed route in the shortest way possible when no direct to a point was given and this could give you an unexpected 90° turn to join his route again. This has led to near misses in the passed.
I guess that what you were saying regarding to give it a heading to resume it's route might be taken in the same way, think you might not for 100%sure know what the acft will be doing exactly, especially since I would guess you wanting it to give it that heading to resume there probably is a reason for this heading and in this case the acft might suddenly leave this heading while you might have still needed the heading for just a little bit longer. I would say the problem with this is that you don't know exactly when the acft will be leaving this heading.

But like I said it might as well be that you were talking about something completely different :D

[reynoldsno1]

With RNAV a pilot can still fly the aircraft manually on a heading to intercept a track to a waypoint - he does not have to actually fly to the waypoint (just like intercepting a radial). It's really no problem....

[DFC]

As the previous poster said, intercepting an LNAV route from a heading is absolutely no problem.

The problem arises in how you tell us to do it.
Some modern aircraft can display the airway structure as a background but you can take it that for the most part, we are not interested in the fact that we are flying along the UL159 ATS route but we are interested in the fact that we are routing from for example a navaid to a fix and then another fix and then another fix and so on along the route.

So if you vector us to one side and then say something like "ABC123 turn left heading 270 from the heading intercept UL159" then there can be a bit of a pause because we were not even thinking about what ATS route we were flying on.

If however, you say resume own navigation direct to POINT then we all know exactly what is required instantly.

If it is radar victors then you should be able to clear us to a suitable point down route when releasing us from the heading since anything else is less efficient but can be done.

It is the non-RNAV people that have a problem with direct to a fix because they need to use a VOR or an NDB to track to that point. However, there are very few around these days (and none above FL100)!!

So yes we can do it but why put us on a 30 degree intercept with an airway centerline when we can do a 5 degree interecept by routing to a fix further along the route.

[BOAC]

You mean you don't use charts or even a PLOG? Heaven help you when the wick goes out.

[Denti]

Charts are on the EFB (no paper charts on the aircraft anymore at all) which you might have to boot up, that takes around 5 minutes, oh, and you have to take the time pre-departure to load all the flight plans on the USB-stick (takes between 5 and 10 minutes, allowed briefing time is max 10 minutes), however flight plans might not be available during briefing time as they are only calculated up to 8 hours in advance, you do get them later on in paper-form, but that isn't readily usable on the EFB. PLOG is there of course, but it only lists major waypoints (boundaries and those with a large change of track), not every waypoint anymore.

[BOAC]

Better keep that wick trimmed, then Denti:)

Regardless of a 'paucity of waypoints' on your PLOG, I assume there is a track and an airway designator? Instant solution to whether or not "we are flying along the UL159 ATS route"?

Don't get me wrong, I lurv "direct tos", of course, but knowing which airway you are on (or off) is pretty basic, albeit a little 'old fashioned', of course.

[DFC]

You mean you don't use charts or even a PLOG? Heaven help you when the wick goes out.


Yes, OFP with ATS Flight Plan and every leg between waypoints with ATS route, track distance etc etc etc. Paper charts also.

However, FMS is point to point to point.

If ATC want us on our own nav going back towards the planned route then they can clear us to a point and see an (almost) instant reaction or clear us to intercept some ATS route and sit there waiting for us to consult the OFP / Paper charts and and making sure that the LNAV track we are going to intercept is indeed the ATS centerline etc etc etc.

-----------

ICAO DOC 4444 requires that when vectored off route and the vectors are no longer required the aircraft is instructed to resume own navigation, given current position as well as magnetic track and distance to a significant point, an enroute navigation aid or an approach aid.

(8.6.5.5 and 8.6.4.2 (b) )

[BOAC]

"ABC123 turn left heading 270 from the heading intercept UL159" is SOOOH easy for a child of the magenta line, though, isn't it? There on your screen is a magenta line which is the planned route along UL159 (yes, probably pretty close to the centreline of the airway too:confused:). So, if naughty ATC don't follow ICAO doc 4444 it should be a piece of **** to fly back onto that airway. You may not WANT to do it, but you can.

Granted ", FMS is point to point to point" but there in front of you is a ******* great picture of where you are and where UL159 is! Shucks, I could even do it with available VOR's, one hand tied behind my back and an eye-patch, not forgetting my trouser-leg rolled up, of course:)

Now, of course if some bright 'm' child has redrawn the route while displaced it takes a little more effort, but it is not impossible......................................

[DFC]

"ABC123 turn left heading 270 from the heading intercept UL159" is SOOOH easy for a child of the magenta line,


Indeed it can be - but have you ever asked yourself why for example London ATC clear you from point to point either through their airspace or to the start of an arrival route. Would it not be so much easier to say ABC123 route UA123 UB456? Most other ATS units also clear aircraft point to point so it isn't a UK thing.

Anyway the answer lies in DOC4444 as I posted above so it makes lettle difference what one can do.


but there in front of you is a ******* great picture of where you are and where UL159 is!


Very much depends on type.

Plenty of types (no so old) flying where you have to consult OFP and/or chart to find out what ATS route one is flying along.


Shucks, I could even do it with available VOR's, one hand tied behind my back


Yes, great but the question was about RNAV. :)