748 / 744 NG FMC cosmetics

[Hardy Heinlin]

Sorry, I didn't mean to write "automatically opens by the on-approach mode"
but "it automatically opens by G/S or G/P capture". (And there are some more conditions; see below.)

I guess most pilots will never get into this phase with a closed window, hence nearly nobody is aware of it. Or Boeing's FMC notes are incorrect.

This is a quote from Boeing's Differences Document:

7.2. G/S or G/P Capture

(NG FMC) With autopilot and autothrottle engaged and the IAS/MACH window closed or blanked, when G/S or G/P captures, the IAS/MACH window will automatically open and the pilot will set the appropriate speed.

(NG FMC) During manual flight with autothrottle disengaged and the IAS/MACH window closed or blanked, capturing the G/S or G/P will not open the IAS/MACH window since there is no A/T mode active.

(747-400 Legacy) For G/S capture, the 747-400 Legacy FMC operates the same as the NG FMC. The Legacy FMC does not have IAN capability and does not support G/P.

[dhob]

Yes of course, speed window opens whenever pitch mode changes to a mode other than VNAV.

Since the post was related to the wind additive on the Approach Ref page, I assumed it was in reference to a NON-ILS approach using VNAV to minimums or End of Descent.

If VNAV isn't the active pitch mode with speed window closed, the FMC speeds have no efficacy whatsoever.

[Hardy Heinlin]

As far as I understand it, this text is about VNAV approaches with VNAV PTH, especially about IAN approaches with VNAV PTH. So, not a mode change, I think.

Note this part in the middle of the above quote:

"(NG FMC) During manual flight with autothrottle disengaged and the IAS/MACH window closed or blanked, capturing the G/S or G/P will not open the IAS/MACH window since there is no A/T mode active."

If this note were about a mode change, the window wouldn't open when engaging V/S or G/S etc.

[dhob]

First, the NGFMC itself does not enable Integrated Approach Navigation capability. The 747-8 has IAN capability due to different FCC's, and upgraded displays which display NPS and IAN scales. The FMC OPC must have the IAN and NPS enabled as well. With all this, the 747-8 uses an FMC generated glide path to create an ILS like display and approach. As such, to capture and fly an approach using IAN procedures, the APP switch is selected which arms the lateral mode (FAC, LOC or B/CRS) and pitch mode (G/P). One captured, G/P becomes the active pitch mode, and the auto throttle mode becomes SPD, and the speed window is opened when captured from VNAV PTH/SPD/ALT. All of of our 747-8's have IAN capability.

The 747-400 cannot fly IAN approaches. Boeing would have to retrofit the 747-400 with the requisite equipment, then accomplish certification with the FAA and issue an updated AFM. No operator has done this nor likely too as the cost benefit isn't there.

With that said, the only method to fly Non-ILS approaches in the 747-400 is with VANV PTH or V/S. For our procedures, we use VNAV (unless it simply isn't available). As stated in a previous post, VNAV PTH is the pitch mode throughout the approach, and the crew must open the speed window manually at some point prior to the FAF. Note all of our 747-400's now have NGFMC's with BP4.0 software.

The reference document you are referring to is a bit vague, and it conflates IAN with NGFMC. Further, the statement; "During manual flight with the autopilot disengaged, the autothrottle disconnected and the IAS/MACH window closed, capturing the G/S or (G/P for the NG FMC) will not open the IAS/MACH window since no A/T mode is active." is not complete. Boeing ends the paragraph with; "Manual flight with the autopilot disengaged, the autothrottle disconnected and IAS/MACH window closed is not a Boeing procedure."

No one would operate the airplane in VNAV with autopilot off and autothrottles off and speed window closed. The FMC would be commanding the speed bug without crew input or awareness, which could cause significant issues.

To reiterate, if VNAV is the active pitch mode, and a mode other than VNAV is subsequently captured or selected, the speed window opens.

[Hardy Heinlin]

I agree with almost everything you wrote. But what you wrote does not resolve that bizzare Boeing text which implies that the window won't open automatically (under the conditions mentioned in the middle part of the text). If you assume they talk about a non-VNAV mode, then the window won't even open while a non-VNAV mode is engaged (in that case).

I understand that the SOP is to open the window manually long before. But I'm just interested in the system logic, i.e. in the question what will happen when VNAV remains engaged and the crew won't open the window manually.

No one would operate the airplane in VNAV with autopilot off and autothrottles off and speed window closed. The FMC would be commanding the speed bug without crew input or awareness, which could cause significant issues.

The issues would be particularly significant when the A/T is engaged. That might be a reason why the window opens automatically in the final phase, in case the crew forgets it. So in the most critical phase the FMC can no longer change the speed bug to an erroneous setting which the autothrottle would chase. In manual flight you have at least your hands on the throttles and your eyes on the speed tape, so you see where the limits are even if the speed bug goes to a nonsense position.

[United744]

From what I've seen of the 7_3_7 NG and 777, the speed window auto-opens at the current speed passing the FAF if it isn't already open. The "gotcha" is if you're faster than flap speed and decelerating, and running the flaps out. It will capture a higher speed, and could bust the flap speed (if that's what you were doing at the time). This is why Boeing recommend you manually open it prior to the FAF.

The wind additive is applied to the approach page VREF speeds. It's not an aide-memoire; it actually adds to the displayed speeds. What it won't do is update the selected approach ref speed - you would need to down-select the speed again.

[Hardy Heinlin]

Further cosmetics:

Only recently I noticed on a real FIX INFO page that flight level values have leading spaces before "FL" when the level is below 100:

FL  8
FL 50
FL190

In PSX:
FL8
FL50
FL190

I think these leading spaces for lower FL values should be inserted on all FMC pages, not just on the FIX INFO pages.

Does anyone disagree?

(I know, flight levels below 1000 feet are not used in real life, but it's possible to set the TA/TL in the FMC below 1000. The display format should be consistent.)


Regards,

|-|ardy

[dhob]

Altitudes must be entered as 3, 4, or 5 digits. Regarding the legs page, if for example the transition level was 5000 such as EDDK, then if 7000 is entered on the legs page, it would display as FL070. Hypothetically, for the three flight level altitudes 70000, 7000, and 700, they would display as FL700, FL070, and FL007 on the legs page. The fix page I'm not sure, I'd have to check but not sure why it would be different. But I don't know for sure.

[Hardy Heinlin]

... display as FL700, FL070, and FL007 on the legs page.

Thanks, glad to hear. I like that better anyway, especially for AB windows:

FL060BFL050A looks better than this 3-piece fragmentation:
FL 60BFL 50A

The downselection in PSX already produces leading zeros, and the upselection too requires leading zeros. It was just the display format in the upper six page lines.

(I can't find that FIX INFO photo anymore. Perhaps it was an older FMC version.)




Leading zeros before "FL" are now implemented in PSX update 10.130. See item 130.03:

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


|-|ardy

[Hardy Heinlin]

Hello,

as you all know, when you enter the destination runway on the REF NAV DATA page (INIT/REF INDEX > NAV DATA), line 3R will display the landing threshold elevation in feet.

In PSX (NG FMC & legacy FMC), the indicated value is rounded to the nearest 10. I think it shouldn't round it.

Also, I think, the length value indicated in 3L should subtract the displaced threshold distance from the total runway length if the entered runway is a destination runway. It does subtract it on the APPROACH REF page in 4L.

Any opinions?


Regards,

|-|ardy

[Mariano]

Hardy,

Would a 767 Pegasus FMC check work?

I will fly again in less than two days. Just let me know.

Regards,

Mariano

[Hardy Heinlin]

Yes, that would help. Thank you, Mariano.

Re runway length: I think it's correct if REF NAV DATA always displays the total length. Assume you will take-off and land on the same runway, and enter that runway on REF NAV DATA, the page won't know if it refers to the one or the other purpose. If it were to refer to the take-off before you take-off, and thereafter refer to the landing, the page would have to change the length display after take-off, and I think that would be a confusing feature :-)


Cheers,

|-|ardy

[andmiz]

 

In PSX (NG FMC & legacy FMC), the indicated value is rounded to the nearest 10. I think it shouldn't round it.

Also, I think, the length value indicated in 3L should subtract the displaced threshold distance from the total runway length if the entered runway is a destination runway. It does subtract it on the APPROACH REF page in 4L.

Ran a quick test for you. 
On the real-world NGFMC it will round airport elevation to the nearest 10 feet. 
Runway 33 in ANC showed as 10865ft on both the ref nav data page and the approach ref page.  The TORA is 10865 for 33 but LDA is 10400, so it doesn't display the LDA. 

[Hardy Heinlin]

Thank you. As you wrote "airport elevation": Did you enter an airport or a runway?

It's strange that the APPROACH REF page doesn't display the actual landing distance available. Did you do the test on the ground before takeoff? My theory: The takeoff/landing mode reference for the display will change when the half-route point is passed. Maybe not for REF NAV DATA page, but for the APPROACH REF page.

As we know, runway waypoints in the FMC database refer to the landing threshold (which may be displaced), i.e. the whole nav system is designed for landing. Now if the FMC always indicates the total length, it will disagree with the length shown on the ND.


Regards,

|-|ardy

[andmiz]

Thank you. As you wrote "airport elevation": Did you enter an airport or a runway?

It's strange that the APPROACH REF page doesn't display the actual landing distance available. Did you do the test on the ground before takeoff? My theory: The takeoff/landing mode reference for the display will change when the half-route point is passed. Maybe not for REF NAV DATA page, but for the APPROACH REF page.

I tested with both the airport (PANC) and runway waypoints.  It was tested in-flight, but in the first half of the flight. 

[Hardy Heinlin]

I tested with both the airport (PANC) and runway waypoints.

OK, so the rounded elevation display in PSX is correct. Thank you.


P.S.: It makes sense if the real FMC doesn't show the true landing distance: The real FMC obviously doesn't know the displaced threshold distance (otherwise it could suggest it in small font on the TAKEOFF REF page for the TOGA/FMC position update point). So the real FMC can always just indicate the total length which is stored in the FMC database. Nevertheless, the stored runway coords are landing threshold coords. And I guess the real ND generates the runway strip symbol simply by using the FMC's two landing threshold locations (actually the same as in PSX). So the ND automatically shows the landing distance rather than the total distance.

[Markus Vitzethum]

Hi Hardy,

> The real FMC obviously doesn't know the displaced threshold distance

just as a quick reminder ... we previously discussed this particular item in the past, see this message from 2016:
https://aerowinx.com/board/index.php?topic=3713.msg38407#msg38407

Quote:
"The FMC runway database does store the landing threshold position. (...) It also stores total length and the offset of the threshold." (this refers to the real world 747-400 Navigation Database).

Markus

[Hardy Heinlin]

Hi Markus,

thanks for the confirmation.

Now that raises another question: The ND gets the landing threshold coords from the FMC. If the reciprocal runway has a displaced threshold, the ND cannot show the entire distance from the active landing threshold to the other end.

AAAAAAAAAA BBBBBBBBBBBBBBBBBBBBBBBBBBBBBB CCCCCCCC

AAA = Front displaced threshold distance (not in database)
BBB = ND runway strip
CCC = Reciprocal displaced threshold distance (not in database)

The FMC knows the sum of AAA+BBB+CCC, but it doesn't know the  ratio of AAA/CCC, i.e. it doesn't know where they start and end.


Regards,

|-|ardy

[Markus Vitzethum]

Hi Hardy,

I *believe* it is simpler ... I always thought that the FMC only cares about 1 runway which is the one and only runway which is loaded into the flight plan or the data page. I don't believe it takes into account the opposite runway (e.g. consider EDDF - there is a runway 18 but *no* runway 36 exists!)

So, assume a runway pair 15/33:

For runway 15:
- it knows AAA (offset, stored in the database) and BBB+CCC (length LDA, stored in the database).
  It does not load data for 33.

For runway 33:
- it knows CCC (offset, stored in the database) and BBB+AAA (length LDA, stored in the database)
  It does not load data for 15.

Does that makes sense?

Markus

[Hardy Heinlin]

Yes, got it. But I wonder why the real APPROACH REF page shows the total length rather than the LDA. The page is about landing performance.



P.S.:

Confusing ... confusing ... confusing ...

For PANC 33, the real FMC doesn't show the LDA (10400); it shows the total length (10865).

Theory A: The FMC knows both LDA and total length. (Why on the approach ref page it shows the total length rather than the more interesting LDA, nobody knows; maybe it's a bug.)

Theory B: The FMC doesn't know the LDA, thus it cannot show it by design (not a bug).