VNAV, Descend Via and Embray'ers

I'll even let guys dick with it knowing full well they're going to get themselves into a slight automation corner because I kind of know what to expect, which is a good tool and a good conversation starter.
 
Autothrust Blue said:
True. We can get what you would call a managed descent within some miles of TOD (I forget how many, honestly--I'll look) by putting a lower altitude in the window and hitting descend now in the flight plan, and activating too. It'll drive at 1000 ft/min and then intercept the path. Nifty.

I don't mess with VS in this thing. FPA is pretty cool.
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It's 50 miles from TOD.

I dont understand the reasoning for using FPA (besides on a Loc approach). I'll watch guys go to FPA and then mess with it until they get 1000 or 1500 fpm. Why not just use VS to begin with? Do you just dial in 3* down and hope the VS isn't excessive or it doesn't hit the limit and start accelerating? Learn me.
 
learhawkerbe400 said:
It's 50 miles from TOD.
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Yeah, that. Thanks :)

I dont understand the reasoning for using FPA (besides on a Loc approach). I'll watch guys go to FPA and then mess with it until they get 1000 or 1500 fpm. Why not just use VS to begin with? Do you just dial in 3* down and hope the VS isn't excessive or it doesn't hit the limit and start accelerating? Learn me.
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I subjectively consider FPA "smoother" than vertical speed, and I usually don't use it to command a specific vertical rate, but a specific descent angle. I roll in -1.0 or so and I cease messing with it for enroute descents where the DES NOW prompt is not available.

I'm much more likely to use FLCH in the terminal area, as those are idle descents where speed matters.
 
Maybe it's just the 145 in me, it's either vertical speed or FLCH. I barely see a reason to use FPA, really ever. It's a pretty convenient button to use to go from say magenta FLCH to green FLCH. That's about it.
 
Derg said:
Hilarious how the 319 you can use full boards, but the 320 you cannot (w/ Autopilot on)
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Pop quiz.
What does 1/2 boards selected on the 320 with AP on give you?
1/2 or 1/4? Got to go to full to get 1/2 or is it a placebo switch from 1/2 to full with AP on?
 
Autothrust Blue said:
Yeah, that. Thanks :)


I subjectively consider FPA "smoother" than vertical speed, and I usually don't use it to command a specific vertical rate, but a specific descent angle. I roll in -1.0 or so and I cease messing with it for enroute descents where the DES NOW prompt is not available.

I'm much more likely to use FLCH in the terminal area, as those are idle descents where speed matters.
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Just don't click off the AP. :-p
 
Autothrust Blue said:
Yeah, that. Thanks :)


I subjectively consider FPA "smoother" than vertical speed, and I usually don't use it to command a specific vertical rate, but a specific descent angle. I roll in -1.0 or so and I cease messing with it for enroute descents where the DES NOW prompt is not available.

I'm much more likely to use FLCH in the terminal area, as those are idle descents where speed matters.
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Smoother than VS? Hmm I'd say it's a toss up at best.

So you'll just roll in -1.0 and take whatever vertical speed you get? What if you're only doing 300kts ground speed and it's only five hundred feet per minute down? Or you have a monster tailwind and now it's doing a much higher rate down? You don't check what your VS is once you set your FPA rate? Just cut out that step and use VS bro!!!!

Nerd rant/over.
 
learhawkerbe400 said:
Smoother than VS? Hmm I'd say it's a toss up at best.

So you'll just roll in -1.0 and take whatever vertical speed you get? What if you're only doing 300kts ground speed and it's only five hundred feet per minute down? Or you have a monster tailwind and now it's doing a much higher rate down? You don't check what your VS is once you set your FPA rate? Just cut out that step and use VS bro!!!!

Nerd rant/over.
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1.3-1.5 degrees seems to always produce 1000 ft/min.

I always use FPA, never used VS in this airplane. It's just one less decision to make as far as which of the many vertical modes, but I still always look at my vertical speed.
 
Derg said:
"Depends".

On the airbus, we have (technically) two managed descent modes, which are both "managed".

Here's the split. Once you start down a managed (VNAV) descent path, the airplane will start descending, join the desired vertical path and then assume that once you reach your path, that you will be in a constant descent to all other fixes on the profile as it planned.

Once you get off the lateral path, the aircraft will still presume you're going to continue descending, even though you've had a mode reversion to VS or "open" (same as FLCH).

So when you're back on path, the 'technique' is to re-cruise by re-inserting your cost-index or re-inserting some of the data on your approach flight phase page on your MCDU because until you do that, where the aircraft is still convinced you're descending as it planned previous to your departure from the managed (VNAV) path, even though you've been droning around in a different mode.

The distinction between geometric managed descent and a profile (I think that's what it's called, I'm having a brain fart, save me @PeanuckleCRJ) descent mixed in with a new runway and a new restriction is one of our leading causes of unstabilized approaches in the Airbus.

Things that aren't a problem for the Airbus are big problems in Boeings. Things that aren't a problem in Boeings are a big problem in Airbus. Mix in another few fleet types into an ATC environment that presupposes that all turboprops are Brasilias and all jets have the characteristics of mad dogs and CRJ's, we've got a recipe for hilarity.

Every time I'm arriving in SLC with a new pilot, I start the brief early, talk about the various ways they're going to attempt to bone us and with almost 100% certainty, they will (which is great because it's pre-briefed and we've talked about some mitigation techniques) or make up something completely new and unexpected when the inevitable "ZOOOOOOMG! Uhhh, here's a Gordian Knot, untie it! Contact tower on…"
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The first descent path it creates is idle path, from there it goes on to geometric path. The third type of path is the repressurization path, which I've never seen. Basically, fifi thinks just like the 757 does (and nearly identical drag profile, too). The only difference is that geometric isn't really geometric sometimes- it's sort of a dive and drive on managed once you get near the decel point, and definitely after you get to the decel point. FINAL APP following the brick seems to have less of a tendency to do the dive and drive thing.

To redraw a new idle path, do just what you stated, or go direct to a fix! Recruising is fine and sometimes appropriate far out (As a rule, I don't recruise below FL230).
 
PeanuckleCRJ said:
To redraw a new idle path, do just what you stated, or go direct to a fix! Recruising is fine and sometimes appropriate far out (As a rule, I don't recruise below FL230).
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Perfect, now that's what I was looking for.

I generally don't re-cruise unless there's an enroute altitude change, but I guess the misnomer is that I'll tinker with the approach ref or CI if we started on an idle path in the DES phase and got held at an intermediate altitude and the donut just keeps on trucking lower even if we're still below the anticipated profile.

It beats the "cross XYZ at 120" and the "HOLY CRAP, we're high! Wait, do the math… ehh, not really"
 
Dexter said:
All of Jetcareers after a fully automated, beautifully executed "descend via.."
View attachment 31754
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unable

IMG_7095.jpg
 
I suppose its good to ready these threads. Someday I may need this knowledge. For now it is hitting the 3:1 point and point the nose down. On speed and altitude every time.
 
ASpilot2be said:
I suppose its good to ready these threads. Someday I may need this knowledge. For now it is hitting the 3:1 point and point the nose down. On speed and altitude every time.
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You're way ahead of me. I'm studying all this stuff, kinda. 'Cause for me, normally, all of the above just ends up being reduced to FAST FAST FAST FAST FWAAAAAUUGHHHHH SQUEAK FWAAAAUGH BWAAAAAANNN NRRRRRRP TAXI BWAAAAAANNN NRRRRRRP SZZ FLLLLLLLLLP PSHEEWWWW.
 
Acrofox said:
You're way ahead of me. I'm studying all this stuff, kinda. 'Cause for me, normally, all of the above just ends up being reduced to FAST FAST FAST FAST FWAAAAAUUGHHHHH SQUEAK FWAAAAUGH BWAAAAAANNN NRRRRRRP TAXI BWAAAAAANNN NRRRRRRP SZZ FLLLLLLLLLP PSHEEWWWW.
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I was that way in the 207. The SAAB is easy, 1500FPM and 55% torque gives you just below redline. Then about 25% on approach gives you a nice stable approach.
 
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