Yeh its defo not simulated properly and should never kick you out of LNAV
 

 

LNAV on go-around is a company option

It was brought up on this ages ago on my old thread. And alot of members said so. Will try and look for it

 

I don't think Kyle Rodgers is looking for a link to an old thread where it was discussed but a ticket number where the so called bug was submitted to Technical Support.

What I'm saying is this, and this goes for any bug report:

Submit a ticket with what is wrong, and how it should work, using specific references - FCOM, technical document, video of actual aircraft, or some other method that can be authenticated, and not random assertions from people we don't know, on an internet forum.

 

If you don't have this, we'll at least see the ticket and ask some questions about it - part of going back and looking at the 777 FBW was because of the forum response - but it's hard to take "this isn't right" as justification without some proof.

To clarify, I'm not talking about flight guidance behavior when TO/GA is pressed. We have a mixed fleet in that regard - some will pre-arm LNAV like Joe said, and some will go wings-level and need a roll mode engaged at 500 ft. The NGX works this way, and that's fine.

 

But what I don't believe is a customer option is having the plane drop back into HDG SEL with selection of a vertical mode, AFTER LNAV was already selected. I've only flown the 737 at one airline so I can't speak authoratively for every fleet out there... But that would make no sense. Having the airplane make an uncommanded switch in flight guidance, during a low altitude, high workload phase of flight is genuinely dangerous. What happens the first time a crew selects LNAV to fly a terrain-critical missed, then gets distracted cleaning up / talking to ATC / looking at fuel etc etc and doesn't notice the plane is no longer in LNAV.

 

My only reference is flying misseds in 737s. They don't do this. I can't speak for every fleet in the world... But it sure wouldn't make sense.

Oh and someone asked about approach type. Happens on both ILSs and RNAVs.

 

Anyway, didn't post this to pick on PMDG or anything, just wondering if it was just my install ;-).

Andrew, grab the books and look up a reference for the behavior that your fleet exhibits and pass that along to PMDG on a support ticket. Once vetted, the finding gets entered in a bug tracking system and it gets fixed next update. Much appreciated.

Been speaking to a PMDG tech member and he has no record if this so called bug been reported or i should say a ticket been sent. So if kyle says send a support ticket why not do it guys....

 

He said -

 

Unfortunately we have no documentation from Boeing to back up the findings so it is unlikely to be implemented until such time as we can get that supporting documentation. I will have to look into the new issue you are reporting as I have no other reports of that type of behavior up until now.

Well for me... 'cause I'm lazy I guess. I just posted this wanting to know if it was a bug in my install, and got the answer.

 

I do find their focus on documentation puzzling in this case though. How do you provide documentation for something the airplane doesn't do? The airplane doesn't automatically lock the lav doors when the coffee makers turn on either... but I'll be darned if I could find a reference in the flight or systems handbooks that actually says so. ;-) Maybe in this case, the thing to do after multiple qualified people have pointed this out would be for PMDG to try and find a reference saying this behavior is correct. ;-)

I do find their focus on documentation puzzling in this case though. How do you provide documentation for something the airplane doesn't do? The airplane doesn't automatically lock the lav doors when the coffee makers turn on either... but I'll be darned if I could find a reference in the flight or systems handbooks that actually says so. ;-) Maybe in this case, the thing to do after multiple qualified people have pointed this out would be for PMDG to try and find a reference saying this behavior is correct. ;-)

 

Documentation doesn't always have to come in the form of the "driver's manual" (I said this earlier, actually). It could just as easily come from a video in the plane, a picture, or by proving experience with the jet. The long and short of it is, as I mentioned earlier, we can't just make changes to software based on an assertion of some random person in the forum.

Kyle the pilot i speak to says that shouldn't happen. Hes done countless go arounds in LNAV. I've mentioned to one of your guys at PMDG about what he said.

Kyle the pilot i speak to says that shouldn't happen. Hes done countless go arounds in LNAV. I've mentioned to one of your guys at PMDG about what he said.

 

And I'm sure you can find a pilot that says the 250/10 rule is absolute, or that you need to stay above the MSA on an approach at all times, or that you need always need a current chart in your plane. These are all wrong, and despite the likely good intentions of those pilots, the facts don't agree with what they believe to be true. Being a pilot does not mean you are all knowing when it comes to flying, just as being a controller does not mean you are all knowing when it comes to controlling. It should, but it is not a certainty. (Ever watch new stories of aircraft accidents and just shake your head at how wrong the "pilot" they found to comment on it really is? Just ask KTVU about not verifying things...)

 

I get that you're trying to be helpful, and I get that you may well be passing on valid information, but verification needs to take place. If he's given that to one of the team, then fine, but again: we need a lot more than something that some person has said in the forum. I don't know what has transpired with anyone reporting this specific issue and the team here. I'm simply saying that, if assertions are to be made without reference to the official documentation, then some other form of vetting needs to take place.

 

As I've stated in several other threads like these:

Put yourselves in our shoes. Imagine how many times we get feedback from people who don't know what they're doing and don't know what they're talking about saying something is wrong (just have a look at the forum for all of the "bugs" people are "finding" because they didn't read the intro manual - keep this in mind when we release our next product). Imagine how many bugs we'd be introducing to our software if we simply believed everyone's assertions here in the forum. You wouldn't believe how many people claim to fly these things but drop little hints here and there that indicate they really don't. All that is required is a little proof, and that can come in many forms, as mentioned in the last post.

Understood. Its going to be tough to verify this unless we get pilots from every operator and ask them does this happen. My belief it shouldn't thats what i think. Why select LNAV to track the lateral route when it kicks you out into HDG SEL. How dangerous is that if both pilots have a high work demand and get self distracted forget there HDG SEL and fly the RWY CL off course.

Understood. Its going to be tough to verify this unless we get pilots from every operator and ask them does this happen. My belief it shouldn't thats what i think. Why select LNAV to track the lateral route when it kicks you out into HDG SEL. How dangerous is that if both pilots have a high work demand and get self distracted forget there HDG SEL and fly the RWY CL off course.

 

Well... not a good argument Vernon. The procedure is repeated in training and simulator check rides a lot..., also there is rule number one: First fly the airplane above all else.

Anyway all i can say is then i don't think this is correct logic to kick you out of LNAV into HDG SEL.

Yeh but 400 engage a roll mode, flaps up no lights engage CMD A/B. If you engaged LNAV at 400 its still going to kick you out and not follow the lateral path in the real world? If thats how the logic is? Anyway all i can say is then i don't think this is correct logic to kick you out of LNAV into HDG SEL.

 It could just as easily come from a video in the plane, a picture, or by proving experience with the jet.

 

I can tell you with 100% certainity that the real jet does not disengage LNAV during a go-around when the vertical mode changes, like the NGX does.  It if was correct behavior you would be able to find supporting documentation in the Boeing manuals, but you won't find it, because it's not correct behavior.

If you engaged LNAV at 400 its still going to kick you out and not follow the lateral path in the real world?

 

It's not going to do that.  LNAV is going to remain engaged until you select another lateral mode.

Well... not a good argument Vernon. The procedure is repeated in training and simulator check rides a lot..., also there is rule number one: First fly the airplane above all else.

Right. And the procedure involves selecting LNAV - exactly once.

 

This attitude that pilots are sharp, and are highly trained to never lose focus, is a nice idea... But it's been responsible for a lot of accidents. Telling people "don't forget to do this" is a recipe for disaster when dealing with human beings... because we DO forget. And there are two scenarios when human beings are MOST likely to forget things: low workload repetitive situations (like cruise flight), and unexpected high-workload situations, like a surprise go around. It would be an incredibly irresponsible feat of engineering to include an uncommanded degradation in roll mode ANY time, but the WORST time would be in the clean-up phase of a go around. And if you've ever done any instructing in these kinds of aircraft, you know the standard reaction to task saturation by the pilot flying: tunneling in on the flight director.

 

An uncommanded degradation in roll mode would have killed someone by now, if the real airplane did this. ;-)