FMC option on DES page: Vertical bearing (V/B)

[turbodiddley]

Yes, the V/B and V/B are extremely shallow early in the flight. Those examples I sent were in climb phase or early in cruise phase. The WPT/ALT contraint is very far away, so very shallow descent. It is in real time, from where you are, to the next descent contraint altitude, with no regard to what the active mode is.

[turbodiddley]

Outstanding illustration, by the way!

[Hardy Heinlin]

This quote from the 748 FMC manual is driving me crazy:

3R WPT/ALT - This line displays the reference vertical bearing waypoint identifier and altitude. This line defaults to the same waypoint/altitude restriction displayed on the AT line on 1R but can be overwritten by pilot-entry.

I can't believe that 3R always agrees with 1R when no pilot entry exists. If you are at FL300 and on-path, and 2 nm in front of you is a 170/2000A constraint (2000A just entered to allow a speed constraint entry in the legacy FMC), and 3R would now refer to 1R, it would indicate a V/B greater than 50° and a V/S greater than 9000 fpm. Why should the crew be interested to know the required path to this useless altitude constraint of 2000 ft? If I were on the deck I'd like to know what the current VNAV guidance is doing -- what is its true target fix and altitude for its path deviation indicator, and what is the target angle and V/S to get there?

Same for AB constraints. If something like 30000B20000A is one mile in front of me and I'm at 25000, why should I be interested to see the required path from here to 30000 or 20000? And which of the two values would it use anyway?

I think the text in that manual is not accurate. Also, it doesn't explain all valid entries: If you just enter a fix without an altitude, does the fix entry require a trailing slash? Or does it automatically detect a fully numerical, slash-less entry as an altitude entry, and any slash-less, alpha-numerical entry as a fix entry?

What if there is no manual entry? Is the data then displayed in small font? Edit: Yes, small.

How can the pilot-entry be deleted? By the DELETE key? Or by leaving the DES page?

Honeywell doesn't answer all these questions.


Regards,

|-|ardy


And what if you enter a fix and no altitude over the default data? Will it keep the default altitude with the pilot-entered fix? Or will the altitude field be dashed? Or is it invalid to enter just a fix without altitude?

[Hardy Heinlin]

Regarding the data blanking: Apparently, the FPA data is blank when in climb. I guess the V/B and V/S data is blank as well when the V/B is a climb bearing.

Obviously, the are no plus/minus signs. All values displayed are unsigned positive and refer to the descent. Hence, if they were able to indicate climb bearings as well, those would have to be negative, and that would look unusual. To avoid this, any climb related data is blank instead of adding a minus sign.

Just a theory ...


|-|

[Hardy Heinlin]

Several new V/B features are now available in PSX 10.80:

http://aerowinx.com/board/index.php?topic=4191.0


Regards,

|-|ardy

[emerydc8]

Hi Hardy and sorry for the late reply on this. I had to wait until I was on an aircraft that actually modeled the V/B. I did a video between SFO and LAX last night. We were at FL290 on the IRNM2 arrival. CROWY is the first altitude constraint and, as you can see, it displays under WPT/ALT as well. You can manually insert another fix and altitude but when you delete it, it goes back to the "AT" fix in 1R on the DES page. I inserted SYMON, which has an altitude restriction of 13000B12000A and then CLIFY which has a constraint of 8000B7000A. I don't know if this helps but here's the video. https://youtu.be/vSuOT5W9om4

And what if you enter a fix and no altitude over the default data?

It will say that it's INVALID.

Jon

[Hardy Heinlin]

Thank you, Jon. I will add the "invalid" function for entering a fix without an altitude over the default data.

(Do you know why there is no waypoint in 1L at "E/D AT". There's just a dot "." after "150".)


Regards,

|-|ardy

[emerydc8]

(Do you know why there is no waypoint in 1L at "E/D AT". There's just a dot "." after "150".)

I don't know. We had the ILS 25L installed for the approach. The touchdown elevation for 25L is 98'.

The route distance is about 312 miles and maybe we weren't past the half-way point, so the data for SFO was still displayed if you pulled up the INIT REF and looked at the approach flap/ref speeds?

If you don't enter an altitude with the fix it will say "INVALID ENTRY."

[Hardy Heinlin]

The E/D is independent of the half-way logic and of the runway displayed on the APPROACH REF page. The E/D is the target descent waypoint and its altitude constraint in the active route; it may be a runway or any other waypoint type. In your video I would expect "RW25L" at 1L. "150" makes sense as it's 50 ft above the threshold (above 98 ft rounded).

Maybe your FMC will never show any "RW" waypoint at 1L for the same reason the ND will never show any "RW" in the top right corner? (Just dashes for runways and conditional waypoints in the top right ND corner.)

[emerydc8]

I looked at this again a few hours ago coming in on the BAYST1 Arrival. First, to answer your question about what happens to a pilot-inserted waypoint/altitude if you go to another page and go back. The waypoint doesn't automatically switch back -- it stays there. https://youtu.be/VgAD7uNIn30

As far as the RW25L issue, you can make of this what you want, but I was watching just as we passed SYMON and as soon as it cycled over to BAYST, RW25L appeared (see pic). I don't know why. Maybe BAYST doesn't have two altitude constraints, but JUUSE does and it's the next waypoint after BAYST and 25L remained for the rest of the approach. Go figure.

[Hardy Heinlin]

Now this photo is shocking me -- for a different reason :-)

It disagrees with my theory. It shows the V/B to a soft constraint, namely to 9000A. The V/B is 6.1°, and 3307 fpm are required to get there -- even though it's just an "A" constraint. So the V/B target indeed always agrees with 1R (unless it's manually entered), and it does not show the true target of the current VNAV guidance; VNAV certainly isn't guiding to 9000 in this scenario.

Well, what target altitude does it use when the active constraint is an AB window? The nearest of A or B?

What's the purpose of this function anyway? Does it show you how far you are on the safe side of an A/B limit? E.g. in your scenario, you are (I assume) nicely riding on the VNAV path which is currently 2.4° -- and the V/B display tells you: "No worries with the 9000A; it's way below your current 2.4° path." Is it that kind of info it's designed for?


Thanks,

|-|ardy

[emerydc8]

What's the purpose of this function anyway?

Sorry, I've never used it. I know very little about it. In my video, we were descending in VNAV PTH.  After BAYST there is JUUSE (9000B8000A), CLIFY (8000B7000A), and the hard altitude at DWYER (210/7000).

[John H Watson]

https://www.pprune.org/tech-log/445157-fpa-v-b-v-s-b737ng.html

"Most restrictive altitude target?"

[Hardy Heinlin]

You mean in an AB window, it takes A or B whichever is "most restrictive"? Or in other words: Whichever is closer to the current path.

Or do you mean in general? That was my theory * -- which is wrong obviously. The target in 1R is not always the most restrictive, it's just the first one.


|-|


* http://aerowinx.com/board/index.php?topic=4872.msg56663#msg56663

[John H Watson]

Sorry, I haven't been following this thread. I thought the poster meant that the V/B ignored the A & B and just went for the next hard altitude waypoint. That is not to say that VNAV ignores A & B.

Is V/B just a general guide to be used with common sense just like the green banana?

[Hardy Heinlin]

It's linear anyway, like the banana system -- unlike the offpath descent feature which is non-linear like a VNAV idle path profile.

[emerydc8]

I did this video for you going into SFO on the SERFR 3 Arrival a few hours ago. I'll let you figure it out, Hardy.

Cheers.

https://youtu.be/7XsLluT7ZVE

[Hardy Heinlin]

Thank you, Jon. I just learned two things from your video:

1. The V/B decimal is removed above 9.9, and so the value can increase further with two digits.

2. For an AB window, it uses the B until the aircraft is below the B, then the A.


Regards,

|-|ardy

[emerydc8]

I'm glad someone got something out of it.

BTW, I took a pic of the DES page on the climbout from LAX. I'm not sure why 70 RW28R in SFO is shown here but 150 RW25L to LAX did not appear until well into the IRNM arrival last week.

[Mariano]

Hardy,

I'll be catching up on this post in the coming days.

This is from a Honeywell Pegasus manual. Quite basic, but you might get something out of it.

https://www.dropbox.com/s/qcxiykc4mggqdud/DES%20Page.pdf?dl=0

I'll be at work on Friday. Should you need anything specific regarding behavior that Jon hasn't already provided, just let me know.

Best regards,

Mariano