B737 Descent Questions

[100 above minimums]

Thank you for all your inputs, appreciate it.

@excrab

Thank you for trying but again, off topic. What you explained is quite basically what would happen if you get a shortcut on a STAR, something I'm familiar with already. Look, this is the scenario I am talking about for example: you're 10 miles abeam the runway on a downwind when you do a Direct Intercept course to the FI. In this case, you're on Heading Select and your track is not even intercepting the active flight plan and you're not flying to any waypoint. So, at this point, the descent profile is giving you indications of too high/too low based on how many track miles when you are not really flying on, to, intercepting the active flight plan? Hope this makes my question more clearer.

It is correct, I do work for an airline with manuals at my disposal, thankfully. And while I also have other people who I could ask, I do consider PPRUNE as a valuable resource since there are too many colleagues here with far more experience than I have and I see no shame in asking them. And my ego does allow me to learn from someone with less experience or even not a pilot AS LONG AS he/she is able to provide a reference for what they say, something repeatedly asked for.

[ImbracableCrunk]

Originally Posted by excrab

It's all in the manuals, try reading and learning instead of asking here, or ask the next training captain/check airman you get to fly with, or email your training department. Unfortunately you can never be sure that pprune users are even real pilots nowadays, I could have just made all of that up.

What's wrong with asking here? That's kinda the point of this thread. You don't like the thread, don't read it, crankypants.

[100 above minimums]

It is indeed very ironic for him to say that one should not ask for help on PPRuNe while he himself has a thread started looking for someone to lend him a hand. I'm sure someone ought to have taught him to "practice what you preach" in his 30 years of flying.

[sonicbum]

Originally Posted by poldek77

This statement is correct.
However you must be aware that arming LNAV in such a situation will result in intercepting the final approach course. But sometimes we are not cleared for that as ATC may need us to cross the final track and intercept from the other side for separation purposes.

I'm discussing the technical side of it, not techniques/SOPs.

[RVF750]

Generally, using VNAV all the way and keeping your head inside while being vectored is a depressing consequence of the modern way of teaching. You never see a chap or lass who has come up via turboprops, instructing or GA who do this. Because they can actually fly an aeroplane, not a computer game.

As stated above, the 737 FMC does it's calculations in reverse and once under vectors and human guidance from the ground, it isn't really that good at it. The further you deviate from the magenta line, the worse it gets, but constantly tapping away is just poor airmanship. Intuition and common sense should suffice, but it doesn't seem to anymore.

Finally,V/S and LVL CHG are mutually exclusive. Yo can have one or the other.......

[RAT 5]

but constantly tapping away is just poor airmanship. Intuition and common sense should suffice, but it doesn't seem to anymore.

Indeed; and as most airfields have a DME on site one would hope a competent pilot wold be able to make a reasonable calculation about the glide path proximity when off the magenta line. But as you say "it doesn't seem to anymore." One reason could be that some operators insist/SOP on LNAV/VNAV update to the OM at all times when off the STAR. i.e. the pilot has been discouraged to use their brains and so like other piloting skills it has become decrepit. I saw it many times, when VNAV gave some nonsense about path error, that the F/O sat there wondering questioning how this could be so, but doing nothing. There were occasions where it said we were high by quite a bit and their hand was reaching for the speed brake, only for it to be refused. "Yes but, it says......." Have a look at the altimeter & DME and think again."...."Yes but, how can it say that????" ......"No idea, but it ain't correct is it." ....."Oh yeah."

[flyburg]

Originally Posted by 100 above minimums

Yea, do try it out and let me know. I'll also try it out on when I get the chance to. But either way, not sure that this is a viable solution; one wouldn't want to arm LNAV while they're only being vectored on a HDG SEL. Would cause a huge mess if during such a phase, with high workload, they inadvertently arm and forget to disarm LNAV.
But more importantly, is there no reference for such thing in the manuals?

very interesting, tried it out, indeed when programming a extended centerline vnav shows a picture as if you where on that centerline, often depicting you high as you are probably still on a base leg(this I knew). When arming lnav it gives you an accurate picture! Going back to hdg select it goes back to the original picture! I did not know this behavior! Couldn’t find anything in the FCOM referencing this (and interested if anybody does have a reference) but it makes sense!

mind you, when arming lnav make sure the wings are level, it then continues on the heading until intercept, if you arm Lnav when in a turn to a specific hdg it starts doing it’s own thing!

learn something interesting from this board all the time.

p.s. Brought up with small aircraft and turboprops and always check all available means to cross check alt v distance but interesting nonetheless!!

[RAT 5]

mind you, when arming lnav make sure the wings are level, it then continues on the heading until intercept, if you arm Lnav when in a turn to a specific hdg it starts doing it’s own thing!

It will go on to a 45 degree intercept. As you say, if on ATC HDG's wings level then LNAV to intercept the centreline will keep the ATC HDG.