Difference between TO TO and TO FROM modes, and why care?

[GregP]

Perhaps my confusion is based on my perception that these modes are very confusingly named: what exactly does "TO TO" mean, especially as it requires a FROM point to be set, while the "TO FROM" mode apparently somehow allows navigation TO or FROM a waypoint, although the manual never explicitly states how you choose between TO or FROM? To make matters worse, the manual doesn't describe the situations in which one or the other might be used, or why.

 

By way of providing some foundational definitions for the following discussion, I quote these comments from the 1.1.1.1 manual:

 

Page 226 ("NAV / Attributes Sub-Page"): "By default, a waypoint's attributes are: Steer: TO FROM"

 

Page 229: "TO FROM - the commanded course is the great circle path along the course entered via the HSI COURSE SET knob to/from the selected steerpoint."

 

Page 229 : "TO TO - the commanded course is the great circle path from the designated From point, displayed on the CDU FROM Page, to the selected steerpoint."

 

I have of course seen

, and I've read and re-read the relevant sections of the manual. Fish's video is an invaluable addition to the manual; however, I've begun to wonder whether maybe some of these things have changed since 1.0.0.8 (the version used when Fish made his video), thus confusing things further for the new learner. For example, from the 1.1.1.0 patch notes:

 

"• Waypoint attributes from ATTRIB page are now correctly applied to a newly created waypoint or markpoint.

• Waypoint attributes are now correctly applied to ADI/HSI steering when the steerpoint altitude/coordinates, current fly-to DB, or current steerpoint number have been changed, or when the ANCHOR point has been set as the steering destination via the NMSP.

• Many fixes have been made to the ADI steering bars logic. Pitch steering will work for the anchor point now. Pitch steering was improved and is less sensitive. Bank steering bar will properly steer to the course set via HSI. Bank steering pointer will no longer generate strange steering commands.

• Course set display on ATTRIB page will refresh when FROM point has been changed."

 

In particular, that second bullet ("Waypoint attributes are now correctly applied to ADI/HSI steering when...current steerpoint number has been changed") would seem to possibly invalidate some of Fish's video because it would imply that in 1.0.0.8 we could never be completely sure whether our choice of TO TO or TO FROM for a selected steerpoint was actually being applied to that steerpoint.

 

I also noticed (see attached pic) that while in the NAV/ATTRIB page, the tooltip over the CDU's LSK L5 (STEER mode) says "Current waypoint steering mode (only TO FROM functional". Is that a remnant of limited functionality from an earlier version? Perhaps related to the second bulleted fix from 1.1.1.0 quoted above? Or is this true for version 1.1.1.1?

 

So, given all the above sources of confusion, my current understanding of the way the TO FROM and TO TO modes work in 1.1.1.1 is as follows (please correct me if I'm wrong -- that's the whole point of my thread):

 

It makes sense to me that the TO FROM mode should be the default waypoint attribute: absent any other information, it seems logical to generally assume that if my current steerpoint is waypoint B, I am probably coming from waypoint A. Since both these points were set up prior to takeoff, it can just be assumed that my FROM point is waypoint A (i.e. I don't need to manually set my FROM point) and thus the course between them is known a priori.

 

If the above is true, I would think that the desired course setting for waypoint B (i.e. coming from waypoint A), moreover, could be found on the NAV/ATTRIB page, and I would need to manually dial this into the HSI in order for the CDI to be referenced properly. However, this mode also gives me the flexibility of allowing manual (i.e. not having been calculated a priori by my known previous waypoint) specification of my desired inbound course toward waypoint B, in case I want to approach from some other direction than from waypoint A. In that case, rather than enter the course shown in the NAV/ATTRIB page into the HSI, I enter whatever course I want, and the CDI will be properly referenced to that course.

 

The TO TO mode, in contrast, seems to me to be primarily useful in a situation where I know I want my current steerpoint to be waypoint B, but I am not coming from waypoint A and would like to manually a choose a different waypoint instead. Thus I manually set my FROM point in the NAV/FROM PT sub-page; a course would be calculated between these two points and would be shown on the NAV/ATTRIB page; and from there I would enter that course into the HSI in order for the CDI to be properly referenced.

 

So -- is anything wrong with what I've written above? In some sense this is probably a minimally-relevant issue for many Hog drivers since, as long as you have a functioning HUD and TAD, you don't really need to ever refer to the HSI or ADI in order to navigate between your waypoints. But I've avoided the intricacies of the CDU for too long and have finally decided to tackle it, so I'm trying to figure this all out. My feeling is that if different modes are provided, there must be some good reason for it; and that if I don't see any need to understand or use them, I'm probably missing something.

Edited May 2, 2012 by GregP

[hassata]

No that's a question lol. Hope someone can shed some light as well.

[BlueRidgeDx]

I'm writing from memory, on my iPhone, in class, so I'll have to check the Dash-1 when I get home to make sure I'm not remembering it wrong.

 

TO FROM mode treats the steerpoint just like a VOR. You can set the HSI Course knob to whatever "radial" you want, and the HSI will act just like when navigating TO/FROM a VOR.

 

In TO TO mode, it assumes you want to fly a great circle route between a known waypoint or markpoint and the current steerpoint. You need to manually set the HSI Course knob to the course indicated by the CDU. This is not strictly required because the CDI will indicate correctly regardless of the Course set, but you don't want to fly around with the Course pointer pointing in the wrong direction.

[Fish]

Think its covered in detail here.

 

Edited May 2, 2012 by Fish

[GregP]

Think its covered in detail here.

 

 

Didn't actually read my (admittedly long) post, did you? :)

Edited May 2, 2012 by GregP

[GregP]

TO FROM mode treats the steerpoint just like a VOR. You can set the HSI Course knob to whatever "radial" you want, and the HSI will act just like when navigating TO/FROM a VOR.

 

In TO TO mode, it assumes you want to fly a great circle route between a known waypoint or markpoint and the current steerpoint. You need to manually set the HSI Course knob to the course indicated by the CDU. This is not strictly required because the CDI will indicate correctly regardless of the Course set, but you don't want to fly around with the Course pointer pointing in the wrong direction.

 

Yup, that all sounds pretty much in agreement with what I thought. Thanks!

 

That still leaves me with the question though, about whether that CDU tooltip is correct or not, i.e. is it really true that only the TO FROM mode is currently functional?

 

And also, if the 1.1.1.0 patch fixed a bunch of previously broken functionality regarding steer modes and ADI/HSI/CDI indications, perhaps Fish's video isn't quite showing us what it should be, at least as of 1.1.1.1 (through no fault of his own, obviously). In that case ... hey Fish, any chance you'd remake it? :)

[Fish]

Didn't actually read my (admittedly long) post, did you? :)

 

Apologies, my bad, i diden't :doh: and thanks for your kind comments.

Edited May 2, 2012 by Fish

[BlueRidgeDx]

To the best of my knowledge, all of the modes work correctly now, though some were bugged at release, chiefly SCS and the 3D function. I also haven't seen Fish's video, so I can't comment on that until i do.

 

You should see the difference in HSI and CDI behavior described above, as well as different CDU prompts. In TO TO mode, it should tell you to "SET HSI COURSE TO xxx", where xxx is static and represents the course between the two waypoints (remember that the CDI will indicate correctly regardless of the set course), whereas TO FROM will display "HSI COURSE SET TO xxx", where xxx changes to reflect the course set via the course knob.

 

Again, from memory, so I don't remember if this is displayed on the ATTRIB page or the WP page. I'd have to double check the book at home.

Edited May 2, 2012 by BlueRidgeDx
Punctuation

[Fish]

Edit,

I have changed the bold text below, from NAV to WP.

 

In particular, that second bullet ("Waypoint attributes are now correctly applied to ADI/HSI steering when...current steerpoint number has been changed") would seem to possibly invalidate some of Fish's video because it would imply that in 1.0.0.8 we could never be completely sure whether our choice of TO TO or TO FROM for a selected steerpoint was actually being applied to that steerpoint.

 

Have revisited this and done some testing with 1.1.1.1, but cannot comment on the manual.

 

1. 3 ways to change the steer attributes, a) plan screen, b) CDU-FPM, c) CDU-WP, only a and b work (same as 1.08 ).

2. Only the current SP matters for TO-TO or TO - FROM mode. (don't think TO-TO is releavnt for anchor points).

3. The CI is slaved to the course between the last and the current SP, IF the current SP is in the TO-TO mode. Say we have wp1,wp2, and wp3. if we select wp1 as sp, then cycle on to make wp2 sp, the CI will use this course between 1 and 2 IF wp2 is in TO-TO mode. Similarly to slave the CI to the other course between wp2 and wp3, we must cycle through wp2 then set wp3 to sp (wp3 must be TO-TO mode). Or you could cycle forward to wp3, then back to make wp2 current sp. This would have the same effect.

 

You can be sure that you are in the correct mode if these rules are applied, AND, you use options a or b for setting the Steer Attribute.

 

The qouted statement above suggests that you would only have to 'change the current' steerpoint. That's not correct. It matters from which wp you cycle to the current SP, because for non terminal wp's, there always to courses leading to/from them.

 

 

Hope this helps.

 

 

 

From what i can see this functionality is the same as it was in 1.08

Edited May 3, 2012 by Fish

[GregP]

Thanks Gerry! Unfortunately I have less time to actually FLY the sim than to think and type about it, so I haven't been able to verify what you found, but it sounds about right. In that case, my earlier description of my understanding of the modes should be modified to say that TO-TO mode assumes by default that your previous waypoint was the one indicated sequentially previous in your flight plan (i.e. that if your current steerpoint is waypoint N, your previous waypoint was N-1, and N-1 is therefore your FROM PT--I wonder if it shows up on the NAV/FROM PT sub-page automatically?), and that's how the proper course is calculated; but you also have the freedom to designate any other waypoint as your desired FROM PT, and then a new course will be calculated and shown on waypoint properties page.

 

To summarize:

 

TO FROM mode: the default waypoint mode; path to current steerpoint from any desired radial, which must be entered manually via the CRS knob in order for the CDI to be properly referenced.

 

TO TO mode: the path to the current steerpoint from 1) by default the previous waypoint, or 2) from any other waypoint designated as the FROM PT. In this mode, CDI will be properly referenced even without manually entering the course via the CRS knob, but it's a good idea to do so anyway so that your Course pointer is pointing in the right direction.

[Fish]

 

To summarize:

 

TO FROM mode: the default waypoint mode; path to current steerpoint from any desired radial, which must be entered manually via the CRS knob in order for the CDI to be properly referenced.

 

TO TO mode: the path to the current steerpoint from 1) by default the previous waypoint, or 2) from any other waypoint designated as the FROM PT. In this mode, CDI will be properly referenced even without manually entering the course via the CRS knob, but it's a good idea to do so anyway so that your Course pointer is pointing in the right direction.

 

Looks like u got the hang of it now.

 

Its unfortunate the attributes from the NAV page does not work, as this would be the most sensible place to change it, and you have the required course visible, to allow you to tune the course dial.

[GregP]

Looks like u got the hang of it now.

 

Its unfortunate the attributes from the NAV page does not work, as this would be the most sensible place to change it, and you have the required course visible, to allow you to tune the course dial.

 

I've been thinking about that, and wondering if it maybe has to do with the position of the AAP dial; p. 229 of the manual, regarding attributes that can be assigned via the CDU when on the NAV / ATTRIB sub-page states:

 

"Waypoint Specific Attributes. These are used when the AAP STEER PT dial is set to MISSION or MARK. These can be uploaded from the DTS or entered from the Waypoint page (new or modified).

 

Flight Plan Specific Attributes. These are used when the AAP STEER PT dial is set to MISSION or MARK. These can also be uploaded from the DTS or created/modified from the Waypoint Attributes (WPTATT) page."

 

That seems to say that waypoint attributes cannot be changed when AAP is set to FLT PLAN (which, on second thought, makes perfect sense). Do you remember how your AAP dial was set?

[BlueRidgeDx]

To clarify:

 

Waypoint specific attributes are used only when the AAP STEER PT knob is set to MISSION or MARK, as you stated. Waypoint specific attibutes are set using the WAYPT 2/2 page. If no attributes have been specifically entered using the WAYPT 2/2 page, then the default attributes in the ATTRIB page will be applied.

 

Flight Plan specific attributes are only used when the AAP STEER PT knob is set to FLT PLAN. Flight plan specific attributes are set using the WPTATT page. If no attributes have been set using the WPTATT page, then the default attributes in the ATTRIB page will be applied.

 

So, for each position of the STEER PT knob, there is a primary and a secondary source of attributes. In each case, the ATTRIB page contains the default fall-back attributes to be used in case they are not specificaly entered using the primary method.

 

An example:

 

Using Flight Plan specific attributes allows you to use the same waypoint more than once in a flightplan, and each occurance of that waypoint can have its own unique attributes. In this case, you would need to have the STEER PT knob set to FLT PLAN, and the attibutes for each occurance of that waypoint would need to be set in the WPTATT page.

 

With any other combination of STEER PT knob position, the waypoint's attributes are set globally through either WAYPT 2/2 (or ATTRIB) pages, and each occurance of the waypoint in the flightplan would be assigned identical attributes.

[GregP]

To clarify:

 

Flight Plan specific attributes are only used when the AAP STEER PT knob is set to FLT PLAN. Flight plan specific attributes are set using the WPTATT page. If no attributes have been set using the WPTATT page, then the default attributes in the ATTRIB page will be applied.

 

Ah-HA! So then not only is that line in the manual incorrect, it's also incredibly confusing. Your explanation makes much more sense.

 

And this gets at a higher-level concept regarding waypoints that I think I've only just now finally grasped: all waypoints originally exist independently of flight plans (i.e. flight plans are always considered to be choosing from a set the same size or larger than the total number of waypoints included in the flight plan), and when you pull a waypoint into a flight plan and change any of its attributes, that attribute change does not get back-propagated to the original waypoint that exists outside of the flight plan. By including it in a flight plan, you're essentially creating a copy of that original waypoint, so that any change you make to the copy does not actually affect the original.

 

Example: AAP STEER PT dial is set to FLT PLAN and I'm looking at my flight plan on the TAD. My flight plan includes 3 waypoints: 0 (INIT POSIT), 1 (MSN001), and 2 (MSN002). By pressing the FPM FSK and then selecting my flight plan, I can look at each waypoint's attributes. Assuming that their default steer modes were TO-FROM, I could change them all to TO-TO. I confirm here that all 3 waypoints are now using TO-TO mode -- but importantly, this only tells me the mode that these waypoints are in when they're part of my flight plan.

 

If I exit out of FPM and press the WP FSK and then go into the WAYPOINT sub-page, I will see that waypoint 1 (MSN001) is still in steer mode TO-FROM. How can this be? It's because that change I made before from TO-FROM to TO-TO only affected the instance of waypoint 1 (MSN001) that exists inside my flight plan -- it did not affect the 'original' waypoint.

 

On a related note, one thing that confused me about Fish's video was that, when he's demonstrating the TO-TO mode, his CDU screen shows TO-FROM. But this is because he's on the NAV/ATTRIBUTES sub-page, which only shows the default steer mode for all waypoints -- it will not indicate what the current steerpoint's steer mode is. To see that, he'd have needed to be on a different CDU page, according to the position of the AAP STEER PT dial: if it was on FLT PLAN, he'd have needed to be on the FPM/WPTATT page; if it was on MISSION or MARK, he'd have needed to be on the WP/WAYPOINT/PG2of2 page. The reason why that was so confusing for me in his video was because even though the steer mode continues to show TO-FROM as he cycles though waypoints, an updated "DIAL HSI TO XXX" message would show for every waypoint he cycled through (indicating that TO-TO mode was being used on each waypoint). But, again, this is because the steer mode shown on the NAV/ATTRIBUTES page is only the default steer mode for all waypoints, and does not indicate anything about the actual current steerpoint.

 

So Gerry, your comment above that "CDU-WP doesn't work as a means of changing a waypoint's steer mode" is (I presume) explained by the fact that you probably had your AAP STEER PT dial set to FLT PLAN, in which case, it makes sense that changing the steer mode there was not affecting the waypoints that were in your flight plan.

 

Also, I agree with your comment that "Its unfortunate the attributes from the NAV page does not work, as this would be the most sensible place to change it, and you have the required course visible, to allow you to tune the course dial"; or, stated maybe more clearly, it would be nice to have some CDU page that both allows you to change a flight plan waypoint's steer mode AND gives you the "DIAL HSI TO XXX" message; it's strange that that message ONLY shows up on a page that does not reflect current steerpoint information.

[Fish]

......So Gerry, your comment above that "CDU-WP doesn't work as a means of changing a waypoint's steer mode" is (I presume) explained by the fact that you probably had your AAP STEER PT dial set to FLT PLAN, in which case, it makes sense that changing the steer mode there was not affecting the waypoints that were in your flight plan.

 

Yes, that was my bad, and i did not see the significance of changing the attributes in anything other than the FLT PLAN mode. I have now tried making some marks, and changing the attributes, and can confirm that TO-TO and TO-FROM work. While we might not often need to change these attributes, i could see the sense in being to change for example the 2D/3D attributes.

 

 

So another summary.

 

1. You can change the attributes only on a per waypoint basis, and how you do it depends on the waypoint type.

2. You change a default flight plan wp's attributes through the WPATT page (from the FPMENU), in the FLT PLAN mode.

3. You can change the mark wp's attributes through the WAYPT page 2 (frm the WP MENU), in the MARK mode,

4. You can change the added wp's attributes, through the WAYPT page 2 (frm the WP MENU), in MISSION mode.

 

I'm still not clear about is the function of the attributes on the ATTRIB page (from the NAV page).

[GregP]

I just did a whole bunch of testing in-game, and wanted to comment on earlier statements:

 

Waypoint specific attributes are used only when the AAP STEER PT knob is set to MISSION or MARK, as you stated. Waypoint specific attibutes are set using the WAYPT 2/2 page. If no attributes have been specifically entered using the WAYPT 2/2 page, then the default attributes in the ATTRIB page will be applied.

 

Agreed and verified in-game.

 

Flight Plan specific attributes are only used when the AAP STEER PT knob is set to FLT PLAN. Flight plan specific attributes are set using the WPTATT page. If no attributes have been set using the WPTATT page, then the default attributes in the ATTRIB page will be applied.

 

Agreed and verified in-game.

 

1. You can change the attributes only on a per waypoint basis, and how you do it depends on the waypoint type.

2. You change a default flight plan wp's attributes through the WPATT page (from the FPMENU), in the FLT PLAN mode.

3. You can change the mark wp's attributes through the WAYPT page 2 (frm the WP MENU), in the MARK mode,

4. You can change the added wp's attributes, through the WAYPT page 2 (frm the WP MENU), in MISSION mode.

 

Agree with all the above.

 

I'm still not clear about is the function of the attributes on the ATTRIB page (from the NAV page).

 

The function of the attributes on the NAV/ATTRIBUTES page is that, as BlueRidgeDX stated, these serve as the default attributes for any new waypoint that you add (MARK, MISSION, or FLT PLAN).

 

Some other interesting things I found:

 

- If I create a new mission in the mission editor, all the waypoints default to TO-TO mode and 3D. If I then go in-game and check their attributes on the WP/WAYPOINTS page, they all say TO-FROM and 2D; but if I check them via the FPM FSK, they all show properly as TO-TO and 3D (with the exception of the very first waypoint, which as Gerry pointed out in his video will always be TO-FROM since there is no FROM PT defined for this waypoint). Isn't that strange, though? It seems that the default attributes set in the NAV/ATTRIBUTES page, which should only apply to new waypoints, also affect the waypoints created in the mission editor when they are viewed from outside their flight plan.

 

- If I change a waypoint's steer mode via the WP/WAYPOINTS page, then go into FPM and insert a copy of this waypoint (as opposed to creating an entirely new waypoint) into the current flight plan, the newly-created waypoint's steer mode is not the one that I just set; rather, it's the one specified in the NAV/ATTRIBUTES page which (I thought) should only apply to completely new waypoints. That doesn't seem right either, does it?