Difficulty Forcing FMS out of VNAV CLB

[emerydc8]

Hi Hardy,

I discovered an issue with the VNAV page while doing some engine-out work at JFK. It's a minor issue, and it takes some work just to get to it, but I thought you might have some thoughts on this. Maybe I'm doing something to cause it.

Here's the situ file.
https://drive.google.com/file/d/0B-WRh0Hf7VdZTlc4UkVUcGVaZDQ/view?usp=sharing

I set up the Kennedy One Departure and Bridge Climb on RW 31L at max takeoff weight. There is an engine #1 severe damage (FOD) programmed in right after V1. If you want to fly it with all the (Atlas) procedures, I wrote all of those on the page to the right.

If you just want to fast-forward to where I am having an issue, and you can deal with the engine failure after takeoff, turn left to a heading of 150 and stop your climb at 3,000'. When you level off you will be in VNAV ALT. (Actually, the instructions I wrote might be helpful for anyone who seriously wants to see what is procedurally involved with doing a V1 cut.)

Once at 3,000' and heading 150, you are basically on a downwind to 31L. Load the ILS to 31L and extend the intercept from the CF. Now, try to descend to 2,000' in VNAV (put 2000 in the MCP and altitude intervene). It won't descend because it's still in VNAV CLB.

I think it should sequence to CRZ when the ILS approach is installed. As a backup, I went to VNAV 3/3 and executed DES NOW. When I did this, it blanks the DES page and takes out all the altitudes on the LEGS page for the approach. The FMA indicates |SPD|HDG SEL|VNAV SPD| (see the three pics below).

If I re-cruise it to 3000' on the CLB page, it will still not switch over to VNAV CRZ, and it won't descend when I altitude intervene either. But if I re-cruise it and go to the DES NOW and execute, it does start a descent in |THR/HOLD|HDG SEL|VNAV SPD|.

At first I thought this anomoly might have been caused by my selecting the ENG OUT prompt on the VNAV CLB page after cleanup, but it does it even if I don't select the ENG OUT prompt.

I am able to get it to descend to 2,000 in FLCH, so this is by no means an urgent matter. If you don't have the time right now then don't worry about it. Thanks.
Jon D.

https://drive.google.com/file/d/0B-WRh0Hf7VdZanp1TTFLQkQ5RzA/view?usp=sharing

https://drive.google.com/file/d/0B-WRh0Hf7VdZX096d1RVa1BXZGc/view?usp=sharing

https://drive.google.com/file/d/0B-WRh0Hf7VdZMC1aVnlSeWcxM0U/view?usp=sharing

[Hardy Heinlin]

Hi Jon,

that's normal; CRZ mode activation is inhibited while VNAV ALT is engaged. This information is from Peter, and I implemented this inhibit in one of the last PSX updates.

There is a thread on this somewhere on the forum, I think.

To recruise to 3000, just use the ALT mode for a moment. Then you can re-engage VNAV.


Regards,

|-|ardy

[emerydc8]

Thanks, Hardy. I remember discussing this a few months back on the re-cruise issue in the context of setting a lower final altitude when you can't get your filed altitude. We all agreed that the way to get to VNAV PTH is to select ALT HOLD and then select VNAV again.

But I also think that if you didn't want to take it out of VNAV ALT, and you simply altitude intervened after setting in your new cruise altitude, it should go to VNAV PTH. Maybe Peter would be able to check this. I found this in some Atlas training material on re-cruise:

• At level off the FMA displays:
|SPD|LNAV|VNAV ALT|

Note: We must re-cruise using the VNAV page

• Enter the desired cruise altitude on the VNAV page.
• Push the altitude selector button on the MCP...
• The FMA will now display:
|SPD|LNAV|VNAV PTH|
• Re-cruising successful

[emerydc8]

The strange part is that I posted a situ a few months ago where I had to do a return to AMS using VNAV while level in VNAV ALT at FL60. https://drive.google.com/file/d/0B-WRh0Hf7VdZSGpBcnRfNVdicGc/view?usp=sharing

It starts in the VNAV CLB page and it won't descend when you roll in a lower altitude and intervene. When you install the ILS 27, it initially stays on the CLB page and will not descend in VNAV. But after installing the approach, when you set 4000' in the MCP and altitude intervene, after a few seconds, it switches over to the DES page and starts a VNAV descent. Not sure why it won't do it in the JFK situ.

[emerydc8]

I had a friend try a re-cruise in the Atlas sim today and he confirmed that once entering the new cruise altitude, all it takes is a push of the altitude knob to get it into VNAV PTH -- no need to go to FLCH or ALT HOLD then back to VNAV.

Hardy,

If you get a chance, can you take a look at this situ? https://drive.google.com/file/d/0B-WRh0Hf7VdZUXdfcFVVU01nVTg/view?usp=sharing

[Sorry. I posted the wrong situ] https://drive.google.com/file/d/0B-WRh0Hf7VdZTU92QUQzV3N6U1E/view?usp=sharing


I departed JFK RW 22R for Dayton, Ohio. My planned cruise altitude is FL350. I leveled off at 5000' on the Kennedy One departure, so when the situ starts, it is correctly in VNAV PTH (5000 is also on the LEGS page while on vectors after takeoff).

When the situ starts, presume you have to do an air turn-back to JFK. Install the ILS 04R and extend the Course Fix intercept (ZETAL) and execute. Once the approach is installed, ZETAL is in 1L and the rest of the flight plan to Dayton is deleted. At that point, it should shift out of the CLB mode and into CRZ mode.

Also, since ZETAL is now the active waypoint in 1L a T/D point for ZETAL should be created and it should shift from CRZ to DES when the T/D is crossed.

In the situ, PSX stays in the CLB mode and does an uncommanded descent to 2000 while in |SPD|HDG SEL|VNAV ALT| -- away from the MCP-commanded altitude (5000'). 

This function of shifting from CLB to CRZ to DES is very useful for an air turn-back. Aside from the obvious ability to descend in VNAV for a VNAV approach, it is also useful because you are not normally given the benefit of an ILS glide slope on a 2-engine approach during a checkride. Therefore, a common technique for doing 2-engine approaches in the sim is to select an ILS approach and extend it from the runway threshold (e.g., put RW 04R at 1L and extend at 6R with the inbound course).

The instructor will fail the ILS, but he still wants you to make use of VNAV on the approach, which should default to a 3-degree glide path, extending outward from 50' above the 04R threshold. You can use the Vertical Path Pointer ("VPP") for guidance. If you are within 25 miles from the threshold, on-approach logic will be active and you can do a VNAV approach (you have to control the power since you have no A/T on 2 engines).

There is another question I have related to the VNAV modes during an air turnback, I noticed that PSX has the VNAV Deviation Scale appear concurrently, right at T/D where the Vertical Path Pointer ("VPP") is right at zero. Do you have any video of the real airplane as it approaches T/D to see if the VNAV Deviation Scale appears prior to T/D and then counts down the distance (above the VNAV Deviation Scale) that you are below the path until you intercept it? I am pretty sure that the VNAV Deviation Scale appears before the actual T/D point and doesn't just pop up at the point where it intercepts the path and starts down; but it would be nice to confirm this.

Early display of the VNAV Deviation Scale (prior to T/D) is also consistent with the technique used to do 2-engine approaches. Without being radar vectored to final (radar mysteriously goes kaput and they make you find your own way when down to 2 engines), if you extend the final from the threshold as described above, the VNAV Deviation Scale appears while on a downwind and under the path. The guidance given in the training manual is that if you are on a downwind, a good time to turn your base leg is when the VNAV Deviation Scale displays 1000' fly up (1000' below path).

In the real airplane, I don't know if VNAV goes to DES mode when the VNAV Deviation Scale is displayed or if it waits until intercepting the path before shifting. I would guess that the VNAV Deviation Scale actually appears before it goes into DES mode. In any case, I am not seeing any VPP until it is centered and the path is intercepted. Is there a way to display the path information prior to path intercept? Thanks again.

Jon D.

[Hardy Heinlin]

Wow, Jon, I need 3 months to study this text ... :-)

Would it be possible to distill the essential core idea of it into two, three sentences?


|-|ardy

I had a friend try a re-cruise in the Atlas sim today and he confirmed that once entering the new cruise altitude, all it takes is a push of the altitude knob to get it into VNAV PTH -- no need to go to FLCH or ALT HOLD then back to VNAV.

OK.

[emerydc8]

Sorry I wrote so much. I tried to be detailed but I guess it was overkill. Basically, PSX is not going into CRZ or DES mode after installing the approach to return back to the departure airport. If you open the situ and install the approach to 04R with the CF intercept, it remains in CLB mode but descends in VNAV ALT to the CF altitude, ignoring the MCP altitude.

Also, there is no VNAV Deviation Scale until glide path is intercepted. I think it should appear several thousand feet prior to that, but was hoping to confirm this.

[emerydc8]

Hi Jon,

that's normal; CRZ mode activation is inhibited while VNAV ALT is engaged. This information is from Peter, and I implemented this inhibit in one of the last PSX updates.

Just to clarify, in my situ, it won't go into CRZ mode even if you select ALT HOLD before installing the approach to 04R. Why it descends in VNAV ALT is a mystery to me.

[Hardy Heinlin]

Thanks, I'll try to analyse it in one of the next months ...


|-|ardy

[emerydc8]

Thanks Hardy,

After experimenting with this for the past few days, I made a situ that should help you see what it's not doing. Sorry, there is no easy way to condense this to just three sentences. 

https://drive.google.com/file/d/0B-WRh0Hf7VdZeTNnMkxDb3dCQzQ/view?usp=sharing

In the situ, I set the cruise altitude at 4000' on the VNAV page. After takeoff, if you level off at 3000' in VNAV ALT you will never get to your cruise and VNAV will stay in CLB mode. After flaps are up, turn left to a 135 heading. This will put you on a downwind for 31L.

Now, install the ILS 31L with a CF intercept (ZACHS). This should force VNAV into CRZ mode immediately. PSX stays in CLB.

If you re-cruise to 3,000' (your present altitude), execute, then select ALT HOLD, it will go to CRZ. I mentioned in a previous post that it should be able to re-cruise by simply pushing in on the altitude knob while still in VNAV ALT after executing the new 3000' cruise altitude, rather than taking it out of VNAV to get it to shift over to CRZ.

So, there are two issues here:
1. VNAV is not going to CRZ when an approach is installed; and
2. VNAV is not allowing a re-cruise using the altitude knob while in VNAV ALT.

As for extending the course from the runway threshold as a reference for doing 2-engine approaches, I did manage to get the VNAV Deviation Scale to appear when it shifts into DES on a downwind, but the gradient path that PSX draws from the threshold outward is way too low to make any use of it.

If you want to try this in the situ, when on downwind, instead of extending the CF for 31L, just select the ILS 31L and put RW 31L (threshold) in 1L . Extend 315 at 6R and execute. Then, FLCH down to 1500'. Presuming you have already re-cruised, it will shift from CRZ to DES and the VNAV Deviation Scale will appear. Turn base when VNAV indicates you are 1000' below the path, then (1) arm LNAV, (2) arm VNAV, (3) speed intervene, and (4) select 500' on the MCP, just as you would do outside the final on a VNAV approach (LVSA). Make sure you set the MCP to 2000' as it starts to descend out of 1500' in VNAV PTH or it will capture the 500' MCP altitude.

You will see that the path flies you right down to about 100' RA several miles short of the runway, then it seems to realize that it's low and the VNAV Deviation Scale (and PROGS 2) will show around 2000' low. So I suspect this technique of extending off the runway threshold may never have been contemplated in PSX, but in the Level D sim, it is used regularly for 2-engine approaches where no glideslope is available.

Thanks,

Jon D.

[Britjet]

Hi Jon,

You seem to be building in some caveats here which I would disagree with. I'm not sure of the source you are using but...

Executing an approach procedure as you describe before reaching your cruise altitude does not automatically activate cruise mode. I have seen this situation many times. Indeed, mention is made specifically of the need to reconstruct a vertical profile if returning following a go-around where the prescribed go-around altitude was not reached. Time and time again we had to re-insert a cruise altitude, rebuild the vertical profile and get to VNAV PTH before we could make the approach.

The method that was used (and worked!) to see if VNAV was going to work for you was to press the VNAV button on the FMC ONCE. The page that appears is the mode you are in, as I am sure you know. If it said DES then you should have a deviation pointer. If it said CLB or CRZ then you should have a T/C and/or T/D as appropriate. If you didn't have these then the approach would not work as advertised.

I have to say I disagree that VNAV ALT will go to VNAV PTH just by executing a new cruise altitude in the FMC despite what your colleague says. It just doesn't do that, at least not on machines I have used. I have seen this situation many, many times in the real aircraft, and you always have to exit a VNAV Mode and then select it again.

Cheers!

Peter

[emerydc8]

Thanks for the input, Peter. I don't know what to say about the re-cruise using altitude intervention. The check airmen are instructing that this is the way to re-cruise and it works in their sim. Could it be that the logic is wrong and it has caused them to erroneously believe that it should work this way? I don't know. If you have tried this in the real plane and couldn't get it to re-cruise without taking it out of VNAV ALT, then I would presume you are right.

As for a new approach shifting it into CRZ mode, I was relying on the section of a training manual below (specifically the last two bullet points). If this is incorrect, as you assert, then PSX is correct here and I would not want it to be changed. I am going to follow up on this more and get back to you. Sadly, none of this stuff is found in any Honeywell or Boeing publication. Cheers! Jon.

Return for landing
 Complete any non-normal checklists and then recall review:
o PF: Recall review.
o PM: For non-normal EICAS messages, it is not necessary to push the Recall switch. SCC Standards DEC 2015. Read all EICAS messages aloud. Items affecting the approach and landing are briefed as CRM items during the briefing. If no EICAS messages: No items.
o PF: Cancel.
o PM: Cancel the messages.
 The crewmember with ATC responsibility should notify ATC of any emergency, request the weather conditions, and request vectors to return for landing.
 Contact company if time is available for maintenance, flight operations, and dispatch as necessary.
 If returning to your departure airport, there is no need to enter the airport into RTE page 1. Go to the DEP/ARR page and enter the desired approach. On RTE page 1 you can insert the new landing runway to remove the departure runway. This will allow the correct runway length to display on the Approach page.
 If diverting to an airport other than the departure airport, you must enter the airport into RTE page 1 and EXEC. Go to the DEP/ARR page and enter the desired approach from the new airport. A heading to fly for situational awareness can be made by selecting the new airport into the FIX page and make a 10 mile ring around it. When an approach is put in, fly to the intersection of the final approach course and the 10 mile ring.
 After the flaps are up or at the desired position, call for the After takeoff checklist.
 Selecting the approach page will display the current aircraft weight. This can be useful for fuel jettison or overweight landing considerations.
 Fuel jettison. Use the Fuel jettison checklist. Fuel to remain = 302 - ZFW (on INIT REF page). The Captain may decide to land over weight if it is the safest course of action. FOM 10.2.4.
 8F: See the overweight landing QRH checklist. Section 0, Miscellaneous.
 The VNAV CLB phase will change to CRZ phase when an approach is entered and executed.
 Prior to approach entry in the CLB phase. The aircraft will not descend using VNAV while in the VNAV CLB mode. To descend while in the VNAV CLB phase, use FL CH. Pushing VNAV on the CDU will display the current VNAV phase. After a new approach has been entered and if a descent is desired using VNAV, select DES NOW> on the VNAV DES page to get VNAV into the DES phase.

[Britjet]

Hi Jon,

Thanks for the notes. Interesting. What they are discussing is a diversion, where the destination is modified.
I think that if you modify your destination, as per the notes you quote in bold, and THEN select an approach, then the vertical profile will be reconstructed, and it is possible (although perhaps not certain) that a CRZ phase will be initialised (you might be past TOD?).
I think, though, that unless you re-initialise the route by putting in a new destination this won't happen.

Pressing DES NOW (as per the notes) will force the DES phase as they say, so I would say I agree with that.

With regard to the-cruise. If, say, you have FL350 as CRZ and level in VNAV ALT at (say) FL310, them if you enter FL310 and execute it won't change the mode. I am prepared to fly naked on the next Simfestuk if that isn't correct!

Cheers,

Peter

[emerydc8]

What they are discussing is a diversion, where the destination is modified.

I will check with the guy who wrote this and see if I can find out.

With regard to the-cruise. If, say, you have FL350 as CRZ and level in VNAV ALT at (say) FL310, then if you enter FL310 and execute it won't change the mode. I am prepared to fly naked on the next Simfestuk if that isn't correct!

Hillarious! Hard to argue with someone who's willing to go that far! If you are wrong, you know the next Simfestuk will not be a family event?

I will do some further investigation on both of these. Thanks again!

Jon

[Hardy Heinlin]

Hi Peter and Jon,

I think you are misunderstanding each other.


Jon wrote:

I had a friend try a re-cruise in the Atlas sim today and he confirmed that once entering the new cruise altitude, all it takes is a push of the altitude knob to get it into VNAV PTH -- no need to go to FLCH or ALT HOLD then back to VNAV.

Peter wrote:

I have to say I disagree that VNAV ALT will go to VNAV PTH just by executing

Peter, Jon means the white round MCP ALT button, not the EXEC key.

Jon, Peter thought you mean the EXEC key, not the white round MCP ALT button.

I see no disagreement between the two opinions :-)


|-|ardy


To be precise, the sentence should probably read:

"I had a friend try a re-cruise in the Atlas sim today and he confirmed that once the new cruise altitude is entered and executed, all it takes is a push of the white round MCP altitude knob to get it into VNAV PTH."

[emerydc8]

Good catch, Hardy. Hopefully you are right and we are in agreement here.

I did hear back from the check airman. He had some interesting information to share and I don't think I would have ever considered it had he not been thoughtful enough to reply. Maybe you guys can give me your thoughts on this.

The DES NOW> function is only available in the CRZ mode. It is not selectable in the CLB mode.

If he's right, I guess the option of using DES NOW to get out of CLB mode is an exercise in futility. I thought this was one of the options that I could use to shift from CLB to CRZ, but he's saying it only works in CRZ.

So, there is the other option of getting out of CLB if you need to return to your departure airport -- installing an approach for a return. I don't think his notes above were just talking about diverting to a different airport, as Peter suggested:

When we depart on a normal takeoff with a cruise altitude of say FL 220 for example, the vnav mode will only change to cruise if we put in an approach at our return airport and execute it and our current altitude is at or above the highest approach altitude. [Emphasis added]. So for example in JFK, the highest approach altitude is 3000 feet. If I have not obtained 3000 feet, vnav will remain in CLB mode.

This is why I do not allow pilots to level off below 3000' during training after a takeoff from JFK. They usually try to request this after a V1 cut. If we have obtained 3000 feet and put in another approach, VNAV will change to CRZ mode and a T/D should be displayed on the ND. If no T/D is displayed, push the VNAV button on the CDU, you will find that you are now already in the DES mode.

It sounds like he believes the FMC is looking at the entire nav database for that airport and not just the approach you happen to be installing. He is right that there is no CF or FF at JFK that is higher than 3000. This was my incorrect conclusion. I verified that he meant to say the highest altitude on the approach you install. So, as long as you climbed to 3,000 at JFK, it doesn't matter which approach you select, when you select it, the FMC should go to CRZ.

Now, for the part I'm hoping Peter and I agree on:

As far as re-cruise, if you have to do it, which normally you would not, selecting the current altitude on the CLB or CRZ page, all you would have to do is push the altitude selector to go from VNAV ALT to VNAV path. You will then be in the CRZ mode and a T/D will  be displayed or it may go right to DES mode depending if an approach has been entered and your current location along the vnav path.

He also draws a distinction between getting out of CLB mode for a return to departure versus getting out of CLB mode after a missed approach.

The missed approach is a little different too. When TOGA is pushed, vnav changes to CLB mode. When at the highest of MCP altitude or the missed approach top altitude, vnav will change to CRZ mode. If you level off at an intermediate altitude you will be in VNAV ALT. Put a new approach in and you should see a T/C and a T/D. If you get on approach course you will go to DES mode at the T/D and  the vertical path deviation indicator is displayed.

[Addendum]: I'll see if I can clarify what is meant here. When you level at an intermediate altitude and install the approach, does it go to CRZ or right through to DES when it reaches the T/D? I have a friend in training right now and he is absolutely certain that it goes to DES mode without re-cruising at some point after installing the next approach, even though he never gets to his missed approach altitude for the previous approach. He can't remember whether or when it goes to CRZ, but it definitely goes to DES without having to re-cruise.

It is common to be given a three-engine approach with a missed approach and a second engine fire at 1000' on that missed. He has never climbed to the 3000' published missed approach altitude (he has been leveling at 2000), yet he is using the VPP as a guide to turn base (1000' fly up) and also to do the initial descent in VNAV PTH once he intercepts final. You couldn't do this in CLB mode.

It is sad that very little of this information is published in any Boeing or Honeywell maual. Thoughts?

[Britjet]

Hi Jon and Hardy (thanks!)

I think I understood what Jon said first time around - his clarifications in the last post clears the waters a bit...

Jon, that looks OK to me now, to re-cruise in VNAV ALT you must EXECUTE the new level - and THEN pushing the knob should give you VNAV PTH, (although I have a sneaking suspicion that doesn't always work) - it may be something to do with having a large difference in the levels, but to be honest I can't remember for sure - I know that going out of mode and back in always worked and that's why I and others did it that way...

I'm pretty sure your source is correct about DES NOW not being available in climb....

I think what you say about the return after a go-around sounds correct as long as they reach the PATH altitude at some stage beforehand, as you say.  The many different altitude/profile scenarios on a GA or are return make it difficult for me to make a judgement based on my own experience. Your man is probably right, but I think I would have lost the will to live by the time I checked it all..

As an aside - they give you a FIRE on another ENGINE on a 3-engine GA ? I also noticed what you said earlier about removing the ILS on a 2-eng approach as well. I hope this is "training" and not "checking"?. A bit over the top IMHO...

Peter

[emerydc8]

Hi Peter,

Your man is probably right, but I think I would have lost the will to live by the time I checked it all.

He seems to be as interested as we are about this and he intends to check in the sim tomorrow exactly when it goes from CLB to CRZ on the missed approach. He is thinking that it goes to CRZ when you select the new approach and extend the CF (or bring the first fix of the approach to 1L). Then, if you are inside the T/D you will go right to DES mode. What was that you said about being left alone in a dark room on one of your videos?

As an aside - they give you a FIRE on another ENGINE on a 3-engine GA ? I also noticed what you said earlier about removing the ILS on a 2-eng approach as well. I hope this is "training" and not "checking"?. A bit over the top IMHO...

They give you an engine severe damage on the V1 cut and then when you come back around for your 3-engine ILS, they make you miss and give you a fire at 1000' on the missed. Then, miraculously the field goes CAVOK but the ILS and radar are down, so you have to find your own way back.

I can't remember where it was written, but I was never allowed to use the glideslope for the 2-engine approach on a PC. This was true in the DC-8 as well as the single-engine approach in the DC-10. I thought it was in 14 CFR 121 Appendix F for us, but I can't find it there now. Somewhere, it used to say that you would not be allowed the benefit of an ILS glideslope on your 2-engine approach (or 1-engine for the DC-10). Maybe now it's just a carry-over.

The VNAV path, however, is allowed. So, on the 744 they want you to set up for an LNAV/VNAV approach and go through the monkey-motion (LVSA) on the first part of the approach (no A/T, of course). Then they expect you to disengage the A/P around 1000' and hand fly the landing. This is usually where they collapse the gear on your landing and the PC ends with an evacuation checklist.

[Britjet]

We are allowed to use the ILS on a 2-eng app, with the automatics as a preference. It works fine, although a GA with the initial acceleration while descending doesn't work well at all and requires hand flying (which works better anyway).

I am intrigued by your "check airmen" and their methods. I see lots of opportunities here to specifically and positively train a particular item being compounded by adding unnecessary pressure, which just confuses pilots.
Instead of re-inforcing a successful outcome they muddy the waters by leaping into a compound failure, which hardly ever occurs, and just destroys pilot confidence. Ho hum...

Cheers!

Peter

[emerydc8]

My exposure to aviation training is almost exclusively tied to the supplemental cargo operators. Unfortunately, this seems to be where you find a greater number of "out of control" check airmen who really enjoy belittling trainees with impossible scenarios that they dreamed up. Some of these check airmen are malicious and others are well-meaning but just don't understand that it winds up being negative training.

On the other hand, there are some very dedicated check airmen within this group too. The check airman that I referred to above wrote a 159-page training manual, a 165-page systems manual, and a 193-page line ops manual, in size 8 font, to supplement the official training material from his company, which is mostly the typical Boeing/Honeywell garb that causes us to sit around and try to decipher what they meant by it.