VNAV DISCONNECT during climb

[Spin737 102]

Not sure if that's a RW behavior or not. Seems odd to have it drop out of path for one extra push.

 

I have no reference to back that up.

[scandinavian13 5,192]

 

 

I have no reference to back that up.

 

Dan brought up FCOM 4.10.10.

 

I used a reference in FCOMv2 11.31.24 discusses ALT INTV, which I recall mentioning that pressing it a second time will result in a level off (and thus dropping it out of the path). I'd have to go back and check though.

[Driver170 42]

I have no reference either guys.

 

I have brought it to the attention of paul at PMDG

[Bavarian14 0]

Yes, once there are no more constraints/restrictions available to delete, there are no other defined values for an altitude other than that set in the MCP ALT, which then becomes the new cruise FL in the FMC if the MCP ALT is set higher than the FMC, therefore initiating a level off/VNAV Disconnect.

[scandinavian13 5,192]

I have no reference either guys.

 

I have brought it to the attention of paul at PMDG

Brought what to the attention of Paul? Both myself and Dan have referenced the FCOM that mentions this behavior. Either way, if it's not specific enough, that's an issue for Boeing to take up. We didn't write these FCOMs.

[Spin737 102]

Dan brought up FCOM 4.10.10.

 

I used a reference in FCOMv2 11.31.24 discusses ALT INTV, which I recall mentioning that pressing it a second time will result in a level off (and thus dropping it out of the path). I'd have to go back and check though.

 

 

Yes, once there are no more constraints/restrictions available to delete, there are no other defined values for an altitude other than that set in the MCP ALT, which then becomes the new cruise FL in the FMC if the MCP ALT is set higher than the FMC, therefore initiating a level off/VNAV Disconnect.

 

I just read the citations. Nothing in there suggests that the jet will exit VNAV PATH. Is the sim going to CWS P? What mode is it entering if it exits PATH?

 

Vernon might be on to something. I head out in a this afternoon, and I'd love to do a test, but all of our planes have ALT INT deactivated (i.e. covered up by a little plate held on by a tiny screw).

[Bavarian14 0]

I give up.

[Driver170 42]

Vernon might be on to something. I head out in a this afternoon, and I'd love to do a test, but all of our planes have ALT INT deactivated (i.e. covered up by a little plate held on by a tiny screw).

 

Thanks matt but, sorry guys i smell something not right here!

 

Maybe on your next flight matt you could tell the FO to look away while you do this non normal procedure just joking have a good one people !!!

I give up.

 

Yep just don't hit ALT INV twice

[scandinavian13 5,192]

I just read the citations. Nothing in there suggests that the jet will exit VNAV PATH. Is the sim going to CWS P? What mode is it entering if it exits PATH?

 

Vernon might be on to something. I head out in a this afternoon, and I'd love to do a test, but all of our planes have ALT INT deactivated (i.e. covered up by a little plate held on by a tiny screw).

I'm not at all convinced there's an issue here. The FCOM states that a second press will get you the action exhibited in the video (at least how I read it). The initial press begins the climb as expected. A subsequent press would clear a restriction if there were one. In this case, there isn't, so it (as written in the reference I provided) kills the climb.

Thanks matt but, sorry guys i smell something not right here!

 

Maybe on your next flight matt you could tell the FO to look away while you do this non normal procedure just joking have a good one people !!!

Vernon,

 

He's giving up because you're ignoring him. His posts echo what I've been saying and demonstrated. I'm not sure if you're aware of this, but Paul and I both work together and have discussed this. His job affords him a level of access that you (and most others here) do not have to test these things.

 

I'm utterly unconvinced that there's an issue here. Tested. Backed up by FCOM. You're re-opening this opinion based on a real world pilot's suggestion, but he has no operational experience with the feature. I mean no offense to Matt by that, but even he stated himself that the function is disabled in the aircraft he flies. With no experience with the function a hunch might be a hunch, but still...it's just a hunch, and not verified and backed by experience.

 

I'm getting a little tired of you ignoring people's contributions here to fit your own agenda, quite honestly.

[Driver170 42]

Ok kyle maybe i did jump the guns! I do take that back. Sorry!

 

I just like to add what you have said kyle and many others in this thread. Here is what the pilot said on PPRUNE when i messaged him -

 

There's more than one way to skin a cat.

 

I would set FL390 as planned, if ATC gave me an inital climb to FL250 then that's fine, they will probably give higher later. If they specifically say "Due xxx max level for cruise today will be FL250" or similar then I would reset FMC and press. to FL250.

[Spin737 102]

I give up.

 

 

 

I'm not at all convinced there's an issue here. The FCOM states that a second press will get you the action exhibited in the video (at least how I read it). The initial press begins the climb as expected. A subsequent press would clear a restriction if there were one. In this case, there isn't, so it (as written in the reference I provided) kills the climb.

 

 

Objection: Assumes facts not in evidence, gentlemen. Give me a quote and I'll be more likely to agree.

 

I have flown ALT INT planes, and I never saw it do that. That was three years ago.

 

My recollection is that ALT INT will take you up to cruise and leave you there until you dial something lower and it'll start you back down.

 

I just watch your video, Kyle. Thanks for doing that, but I don't think ALT INT will cause ALT HOLD.

[pcubine 143]

I am doing the second flight right now where I entered an immediate cruise altitude of FL260 in the FMC INIT REF page. The ACT RTE LEGS page showed an altitude of FL260. The MCP altitude was set to 26000. I cruised at FL260 for several minutes the changed then MCP altitude to 38000 and pressed ALT INTV twice. VNAV did not disconnect. The plane climbed to FL380 and leveled off. The ACT RTE LEGS page showed FL380 for each waypoint prior to descent. Pressing the ALT INTV button during the climb did not stop the climb. ???????????????

[Bavarian14 0]

Pcubine, thanks. And that is because it isn't supposed to stop the climb... The whole point of it is to continue the climb regardless of restrictions.

 

Matt, we have extensively provided accurate and legitimate documentation which clearly describes the functions of altitude intervention. We have also clearly expressed that incorrect procedures result in errors. I'm getting to the point of believing that you are now trolling, and quite frankly, I'm getting annoyed with the constant contentiousness. Your "objection" clearly represents your motive to incite some kind of discord here in this topic, and while I can respect you have real world experience, when the manufacturer of the aircraft in question clearly outlines the functions of their automation systems, I tend to agree with their consensus on the matter. Kyle has gone to the point of making a video to help, and now you still want to argue because of "your" experience. Really? 

 

ALT INTV does not cause a ALT HOLD! That is a result of the operator's incorrect usage of the function. The PILOT causes a disconnect/level off by excessive executions of the ALT INT function. The ALT INTV function allows the aircraft to bypass altitude restrictions placed in the FMC or otherwise programmed, either in ascent or descent. When in fact there are no more restrictions to bypass, the ALT INTV looks for a restriction to intervene. The only altitude value at that time left to intervene is the final cruise altitude since all previous altitudes have been dismissed, cleared, or otherwise bypassed. Ergo, If the MCP ALT is set higher than the final cruise altitude, the ALT INTV function will replace the FMC cruise altitude to that of the MCP. Once MCP ALT is reached, a continuous execution of the ALT INTV function will result in a VNAV Disconnect, and level off, since there are no more altitudes to intervene on. The system will replace the FMC cruise level, but since the aircraft is already at that level from the precious execution, it will terminate VNAV since there is no difference in vertical movement either positive or negative with what is programmed, and hence, it will level off and maintain. If in fact the MCP ALT is lower than the FMC cruise level, the ALT INTV will then function as "DESC NOW" in the FMC, initiating a 1,000fpm descent to the selected MCP ALT or to the VNAV Path, whichever comes first. 

 

Vernon's erroneous practices of programming the flight computer and managing altitudes also had inflicted his inability to completely understand how to use the ALT INTV function or as to why the function functioned the way it functions. 

 

So, while I appreciate your willingness to "fact check" us, I would suggest you too read the FCOM and flight manuals and if you continue in your insubordination, that's your problem. 

 

Thanks to both of you for making this issue even more complicated for others who may come along in the future to understand this simple minded function. 

 

I would recommend this topic be locked. Obviously there is no progress being made here and I'm afraid visitors in the future may look at this topic and be left more confused than they came. 

[Driver170 42]

the changed then MCP altitude to 38000 and pressed ALT INTV twice. VNAV did not disconnect. The plane climbed to FL380 and leveled off. The ACT RTE LEGS page showed FL380 for each waypoint prior to descent. Pressing the ALT INTV button during the climb did not stop the climb. ???????????????

Michael Cubine

 

The World On Time

 

Doing it wrong! You THEN NEED to set in the FMC FL 380 and MCP ALT below FL380

Pcubine, thanks. And that is because it isn't supposed to stop the climb... The whole point of it is to continue the climb regardless of restrictions.

 

Matt, we have extensively provided accurate and legitimate documentation which clearly describes the functions of altitude intervention. We have also clearly expressed that incorrect procedures result in errors. I'm getting to the point of believing that you are now trolling, and quite frankly, I'm getting annoyed with the constant contentiousness. Your "objection" clearly represents your motive to incite some kind of discord here in this topic, and while I can respect you have real world experience, when the manufacturer of the aircraft in question clearly outlines the functions of their automation systems, I tend to agree with their consensus on the matter. Kyle has gone to the point of making a video to help, and now you still want to argue because of "your" experience. Really? 

 

ALT INTV does not cause a ALT HOLD! That is a result of the operator's incorrect usage of the function. The PILOT causes a disconnect/level off by excessive executions of the ALT INT function. The ALT INTV function allows the aircraft to bypass altitude restrictions placed in the FMC or otherwise programmed, either in ascent or descent. When in fact there are no more restrictions to bypass, the ALT INTV looks for a restriction to intervene. The only altitude value at that time left to intervene is the final cruise altitude since all previous altitudes have been dismissed, cleared, or otherwise bypassed. Ergo, If the MCP ALT is set higher than the final cruise altitude, the ALT INTV function will replace the FMC cruise altitude to that of the MCP. Once MCP ALT is reached, a continuous execution of the ALT INTV function will result in a VNAV Disconnect, and level off, since there are no more altitudes to intervene on. The system will replace the FMC cruise level, but since the aircraft is already at that level from the precious execution, it will terminate VNAV since there is no difference in vertical movement either positive or negative with what is programmed, and hence, it will level off and maintain. If in fact the MCP ALT is lower than the FMC cruise level, the ALT INTV will then function as "DESC NOW" in the FMC, initiating a 1,000fpm descent to the selected MCP ALT or to the VNAV Path, whichever comes first. 

 

Vernon's erroneous practices of programming the flight computer and managing altitudes also had inflicted his inability to completely understand how to use the ALT INTV function or as to why the function functioned the way it functions. 

 

So, while I appreciate your willingness to "fact check" us, I would suggest you too read the FCOM and flight manuals and if you continue in your insubordination, that's your problem. 

 

Thanks to both of you for making this issue even more complicated for others who may come along in the future to understand this simple minded function. 

 

I would recommend this topic be locked. Obviously there is no progress being made here and I'm afraid visitors in the future may look at this topic and be left more confused than they came.

 

Lol you only fly a 800 pc this man has flew a 41000 tonne plus AC in the real world. Worth tonnes more than your chair and desktop.

[Spin737 102]

 

 

So, while I appreciate your willingness to "fact check" us, I would suggest you too read the FCOM and flight manuals and if you continue in your insubordination, that's your problem.

 

Insubordination. Really?

 

Okay, boss. I'm out.