VNAV frustration

[koutsavd]

Hi,

Althought there have been a number of posts reporting problems
with VNAV, allow me to add myself to the list of complainers.

Since I got the software, I have done 6 flights, with the VNAV
function performing once correctly. The first time I used
it, it was with the FMS tutorial. The plane refused to climb
above 3400ft (alt at MCP was 6000). In most of the cases,
weird things happen. I engage VNAV above 400AGL as suggested,
and most of the times above 1500-2000 AGL. The plane usually
does unbelievable things. First, even without the engagment of VNAV, TO/GA power seems to all the sudden die at 1500AGL (and
I don't mean because of the CLMB mode). Manual throttle is
applied, but ussually the plane is in stall territory.

Let's forget that and let's say I engage VNAV at 500AGL. Then,
I click AP on and guess what, HDG is engaged, Level change is engaged and TO/GA mode disengages with the engines throttling back to idle. It has happened a number of times.

Since I believe that most people are going to write this off to
my inexperience, let me tell you that I get a purple track in the map mode, everything is actived in the fltplan, I have an active flight plan. It is 2AM EST in US and I am still trying to figure it out.

I would appreciate any input on the matter. For the development
team, is this a known issue or not. If it is not, could you please provide us with a flightplan checklist, that would ensure that VNAV works as advertised? What is it that we have
to make sure it happens so that VNAV does not give us grief?
If this is related with an erroneous flight plan, why then the
engagement of the autopilot triggers the engagement of FLT change and HDG given that VNAL and LNAV are not engaged.

Again, please provide some input.

P.S. VNAV works fine after you level off at the first altitude
restriction.

[w6ffc]

First off VNAV works just fine. Now, can you post a screen shot of the panel when it is behaving badly showing the AFDS and the FMC with the legs page displayed? The answer will most likely be very easy to spot. A verbal description of a problem is usually biased toward the way the poster THINKS he is doing things and a lot of time it is a misunderstanding of the facts.(7 years as head of a software company tech support department supports my point of view <g>) Please don't take this as a flame by any means.

As a member of the Beta team, VNAV was one of the main things we worked on and it works just as advertised.

Post a screen shot, we WILL get you flying on the right track..

Mike B.

[sarax]

[font size="1" color="#FF0000"]LAST EDITED ON Mar-09-02 AT 01:27PM (EDT)[/font][p]it' a bit tricky to handle the behaviour of vnav, but i think you can manage it.
take off without anything in the autopilot engaged.
at speed 60 or so click TOGA button first.
takeoff, and at 400 agl engage AP master switch. HDG and lvl chg will also engage automatically. at this time, select LNAV (hdg will disappear)
retract gear and flaps as scheduled. i notice that at this point IAS indicates 270. change it manually to 250. The aircraft will climb correctly up to 10000. Now press VNAV. the speed will increase to 300. and so on...
regards
sarax

PS don't set any altitude restrictions for the first times you practice your climb.

[koutsavd]

Thank you for your time. I can produce a screen shot at this point, but I guess I will have to work on it.

The way I thought things would work (and obviously I may be
wrong here) is that the minute you engage the AP, nothing
on the MCP is engaged automatically and it is up to you to decide what you want. Most propably, this is a result of using
the autopilots provided by MS for the last 10 years that I've
been flight siming.

By the way I am a tech support in a software company, thus,
it is obvious to think of a software defect right away.

Again, thanks for your reply.
Best regards,
Van.

[koutsavd]

Thanks for you reply. It looks like I would have to practice
more when there is a low upper restriction (like 5000ft for
example).

Regards,
Van.