Managed descent, altitude constraints, radar headings

[MonarchOrBust]

You're on a prescribed RNAV arrival, Approach clears you to the IAF and clears you to descend to the IAF altitude, reminding you to meet all altitude constraints along the way. You dial in the altitude given and are happy because you checked and briefed all constraints 10 mins before. Your monitoring is good, the correct modes are engaged yet the old boy on the left mumbles something under his breath. You know what he's thinking, but as it's not illegal to fly the plane like this he lets you be.

About 20 miles before the IAF, you get a radar heading, your lateral mode change results in a vertical mode reversion (On Airbus its Open Descent on Boeing... FLCH?). The heading takes you towards high terrain and the cleared to altitude is no longer appropriate. Old boy then chimes in with "Hah! This is why I don't enter the next altitude until I'm 200ft away". Just as he says that, ATC gives you a better heading to stay clear of terrain as they should and as is one of their responsibilities.

I would like you to imagine this kind of day out and offer your views on the situation particularly with regards to automation, trust in automation, monitoring, ATC.

Thanks!

[pineteam]

On Airbus it will revert to vertical speed not to Open DES. If you are under radar vector, then altitude constraints do not apply anymore… I don’t see any issue here. But oh well I feel you. I remember those days flying with some of these guys.. xD

[BraceBrace]

Indeed no issue. No changes to the cleared attitude and radar vectors, then you should be fine. I always have a depicted MSA on the map but the chart with minimum vector attitudes will be more usefull if available...

[Empty Cruise]

...and then of course Paris where - when given a radar HDG off the STAR you are still required to meet the altitude constraints abeam the relevant points. But - I digress...

[Check Airman]

So on departure, you’re cleared to 5000, does he set 2000 just in case they give you an early level off? In your shoes, I’d keep doing what you’re doing. He can keep mumbling.

[gimbal error]

Well, I might very well be the old boy on your left. Retired just recently.
I flew these types of STARS frequently and I can clearly see the advantages of them. Setting the lowest altitude constraint when cleared was common practice. On the other hand there are a number of factors that kept me from really liking them. The MFS needed to be checked/programmed to the very last detail prior the starting the descend. That takes a while. A short term switch onto a different STAR usually ended in some hasty reprogramming with the result of wrong parameters entered. Been there, done that. During the descend it required a close non stop monitoring of the autoilot modes which keep changing all the time. A quick distraction could let you miss an unexpected mode change with interesting results. Been there, done that too. Setting the next altitude restraint manually continuously during descend could be a safety net to avoid a hairy situation. No big deal, actually increases the mental descend follow up.
Generally I prefered to fly the aircraft instead of watching the computer do its thing. But I may just be another dinosaur about to be extinct.

[FlightDetent]

I am one of those guys, now. Used to say the FCU/MCP takes whatever the ATC clearance is. Crossed the whatever, the refined version is the FCU takes the next cleared altitude.

The narrative is faulty.
a) There'd be V/S as the immediate reversion mode
b) Once the ATC issues heading the clear altitude will still be appropriate or modified.
Sorry to say, the inadequacies of the narrative point to an incomplete understanding of what may be unfolding. Does one feel qualified to critique other people's valid technique then?

Try the RNAV to Varna on a busy day and come tell what use the coded constraints were. Triple the fun if working off Jeppesen database.
DWC arriving from the north-east is another good example.


Now that the side-lines are defined, time to look for some middle ground: Whichever gives you less work, IMHO. Fiddling with the FCU can be a lot of distraction! If the VNAV works it's better to use it as designed, without interventions.

Having just said that, once you get busy with something not on the chart (tfc, wx, atc, crm), keeping the FCU set at the next limiting altitude is an effortless measure to avoid paperwork.

The FMS needed to be checked/programmed to the very last detail prior the starting the descend. That takes a while. A short term switch onto a different STAR usually ended in some hasty reprogramming with the result of wrong parameters entered. Been there, done that. During the descend it required a close non stop monitoring of the autoilot modes which keep changing all the time. A quick distraction could let you miss an unexpected mode change with interesting results. Been there, done that too. Setting the next altitude restraint manually continuously during descend could be a safety net to avoid a hairy situation. ^^^ This. Engraved in gold with platinum letters.

[FlightDetent]

So on departure, you’re cleared to 5000, does he set 2000 just in case they give you an early level off?Que? How does that nonsense connect to a valid, obstacle-clearance based step on the initial / intermediate APCH?

[Check Airman]

My point was that the OP's colleague wanted to do things the hard way, just in case things changed. Why limit it to just that situation? Apply it to the climb as well. :ugh:
If you get a heading while on the STAR, it's going to keep on doing what it was just doing (reversion to VS), and you'll always get an altitude with that heading. It's not that hard.

I've flown with the type of person the OP describes. It's unnecessary workload, and distracts from other tasks. You've already verified all the fixes and associated constraints. Why complicate a simple matter? It's not against SOP though, so I keep my mouth shut.

[FlightDetent]

My point was that the OP's colleague wanted to do things the hard way, just in case things changed.My point the old dog may have seen the heading adjustent coming based on experience, or more likely just tried to get by without getting the fingerprints scalded again.Why limit it to just that situation? Apply it to the climb as well. :ugh:Departing from a field with stepped climb constraints, I do exactly that. Although it's not what you're saying, understood.

[Check Airman]

Here in the US, I can only think of 1 or 2 airports where you'd see ALT CNST in the climb, so it's really not an issue here. I understand Europe to be a bit different though.

At the other end of the flight, some airports (eg MCO) may only have a single constraint. If you set whatever you want there, you probably won't be bitten. At airports like LAX though, there are 13 restrictions from T/D to the FAF. With busy airspace, and constant speed changes, the last thing I need as PM is to have to worry that the PF is gonna bust an altitude.

BUT, as long as it isn't against SOP, I keep my mouth shut.

[FlightDetent]

Roger. Just to double check: Are we on the same page the old man's technique under scrutiny is

a) do use managed descent
b) to shadow the FMC constraints with FCU setting, i.e. never relying on ALT CSTR(*) magenta.
exactly because With busy airspace, and constant speed changes, the last thing I need as PM is to have to worry that the PF is gonna bust an altitude.

[Check Airman]

a) yes
b) no

When I see something other than managed, it's not what (I think) you describe where you manage descent, but keep resetting the FCU. I'll see people do the stepdowns in VS or OP DES. 99% of us just set the lowest cleared altitude and "manage the automation".

[gimbal error]

And yes, I made it common practice to set the restricting MAX Altitudes on the FCU during climb out. Here's why:
VNAV climb out with numerous altitude contraints up to cruise level. All nicely set up in the FMS, double checked all the parameters, AP working in the expected mode, clean up done, zooming up towards cruise altitude, 20 seconds prior to the next altitude constraint you get that "traffic at 2 o'clock, reduce climb to 1500 Ft/min max" call from ATC. A quick push onto that VS button, both heads looking out to catch the traffic. And there goes your altittude level off. Unless you have it set on the FCU.

[FlightDetent]

Got it, just wanted to be clear we'd been poking the same turd. Things getting lost in the translation, even my #12 should say O.M's.T = (a)+(b) more clearly than I actually typed it.

But now it is clear:
(i) use selected vertical modes only;
(ii) use DES but shadow the vertical limits with FCU due to anxiety and OCD issues;
(iii) use DES the way the designers and engineers intended to.

One of the tiny reasons I may subscribe for (ii) on many days is that when a step-down constraint is satisfied the ALT CSTR does not display on PFD. What's the US version of A thousand mosquitos drained the camel, death by a thousand cuts?

Never mind, moving along. How do you (well familiarized) guys feel about using managed speed for deceleration and flap extension - if the ATC scenario allowed it?

[CaptainMongo]

gimbal error

11061252]And yes, I made it common practice to set the restricting MAX Altitudes on the FCU during climb out.

Changing the vertical mode out of managed without resetting the FCU altitude to the next constraint is an SOP violation at my outfit.

[CaptainMongo]

FlightDetent

I have tried it twice over the years, and I wasn’t satisfied with the performance. It didn’t seem to behave like the book said it should. I felt it was slow in slowing down and wouldn’t meet our stabilized approach gates (which aren’t more restrictive than what the airplane should do) I intervened both times.

That said two attempts in so many years makes my opinion merely anecdotal. It may work like a champ, I just don’t have enough opportunities to practice with it.

[gimbal error]

I agree, SOP calls for resetting the altitude on the FCU. But can you see how quickly you end up in a tight corner out of a distraction? And my exerience tells me that we all get distracted too easily. A preset FCU value can safe you lots of paperwork and explaining.

[pineteam]

Captain Mongo your outfit seems like a pain in the @ss. xD
Again I don’t see a big issue of using managed speed and configuring. That’s pretty standard. IMHO, the annoying bit with this is the thrust variation and risk of flaps overspeed when in bumpy conditions and heavy weight. Also the engines will keep spooling up and down during deceleration when configuring unless you are high on profile. I like to have the engines on idle all the way and ask for flaps when the speed is 10 kt below vfe. So to avoid thrust variations I will often select speed Below Green dot and S speed to configure accordingly for a smoother and more efficient transition to VAPP.

[B2N2]

There is no substitute for experience

Let me start with that.
There may be a reason why people do things the way they do in the way they do it.
“Can you teach me why you prefer to do things this way?”
You can always decide later if this is a technique you wish to adopt.

Certain techniques are appropriate in certain situations and not in others.
Try to find out why and you have another tool in your toolbox. You may not always use all of your tools but that doesn’t mean you should discard them.

[gimbal error]

CaptainMongo

I agree, this is not in line with the SOP. But years of experience tell me how easily we get distracted. A preset FCU can safe you lots of paperwork and explaining.

pineteam

Setting the speed bug below green dot or any min manouvring speed is a clear no go. Failing to set the flaps accordingly will put you below min speed which is unacceptable. Again it is distraction that can put you in a very tight corner here.

My general opinion: Setting up backup gates in your AP management does not hurt and can safe you from unpleasant experiences.

[Check Airman]

CaptainMongo

Setting the speed bug below green dot or any min manouvring speed is a clear no go. Failing to set the flaps accordingly will put you below min speed which is unacceptable.

Um what? Since when was it unsafe to fly below F/S/green dot? I set the speed bug to the target speed.

[Check Airman]

FlightDetent

I haven't had much opportunity to let the plane manage the decel. It's mostly impractical here in the US. The few times I have used it, it always seems to slow down WAY too early, and I wind up intervening so we don't drag gear and full flaps in from 10 miles out. I've tried it at local and foreign airports, and it always seems overly conservative.

[pineteam]

Gimbal Error you might want to check the FCTM. You can select speed below characteristics speed provided it’s above VLS + 5kt. It’s only at high altitude that you should not intentionally fly below Green dot speed. This is a common misunderstanding.
FCTM -PRO-NORMAL PRO- SOP-APPROACH
Like B2N2 mentioned beautifully: There is no substitute for experience.
If you were flying into China where ATC ask you to fly at 180kt nm 60 miles from touchdown and your S speed is 185kt you will get use to actually fly below S speed. It’s usually more than 25kt from VLS. Totally fine. Of course you can select flaps 2 but you will burn more fuel.
the 3 times I will definitely select speed below characteristic speed that I can recall are when:
I’m flying at 250kt and ATC asked me to reduce speed to 180kt ( again very common in China) I will immediately activate approach phase if not done already and select 180 kt and ask for flaps 1 at Green Dot and Flaps 2 if required. Yes you can do the Fcom way and managed speed when speed reaches Green Dot ask for flaps 1 and so on but doing so the engines will spool up and down. Not so great.
Second case it’s when I fly a very heavy A321 and green dot speed is less than 5kt from VFE. If VFE is 230 and Gd is 227 and you don’t select a lower speed the engines won’t be on idle and flying into turbulence or cloud you would easily overspeed. The safest way there is to select a speed below Green Dot, allowing the engines to go on idle and once the speed goes below Green dot with a speed trend going down then ask for flaps 1.

3rd case. Anytime during configuration if it will prevent thrust variation.

[TukwillaFlyboy]

All sounds way too complicated.
Fly a Boeing instead. :)

[MarkerInbound]

My understanding is the ADS-B sends the altitude set in the window to ATC. Had another pilot flying the step by step way. Rhein Radar asked us to confirm the level we were descending to because it was different from what was in the window.

[FlightDetent]

The last I flew was a -500 in '03 with U8.5 and it outperformed the Airbus VNAV 4:1.

I could provide a nice explanation why it is a desirable feature and not a bug if someone paid me to, still I hate it when it does what it does the best.

What you read above is folks feeling the same and trying to tweak it. Back before now, choking the throttles did the trick although it was seldom needed.

[pineteam]

I never flew Boeing but I have to admit. The A320 predictions are heavily conservative. If I’m not seeing “more drag” or the v dev at the bottom of the scale on PFD then I know I’m too low already for an idle approach xD.

[Check Airman]

TukwillaFlyboy

It does get complicated at times, but if I flew a Boeing, where would I eat my crew meal, and how'd I know when to retard the thrust levers?:)

[TukwillaFlyboy]

Simple.
When it says “idle” on the HUD

[Check Airman]

Touché. Touché

[FlightDetent]

Check Airman

We need pictures. The question is - how bad can the crew meals get before the table becomes irrelevant and the wish for an airplane with movable throttles resurfaces.

[vilas]

SFO guys who flew Boeing into the boundary wall found Thrust hold complicated. Dubai guys who tried a go around after touchdown and came crashing down never knew that autothrottle/FD is inhibited. Complications never end.

[TukwillaFlyboy]

Experienced Boeing drivers found both of those accidents pretty much incomprehensible.
Really , really dumb.
Can’t completely eliminate stupid , Boeing or Airbus

[vilas]

That's the point. Want to fly Airbus must know Airbus, want to fly Boeing must know Boeing. period! Nothing is that complicated or for that matter that easy either.

[Speed_Alive_V1]

ATC here - with modern Mode-S downlinked aircraft parameters, we can see your MCP selected altitude downlinked to your aircraft coupled tag on our radar screen.
If your downlinked level is different to the cleared level that we have selected, a breakthrough warning message pops up and we will say over RT "confirm your cleared level is FL100" etc. It's a really great tool to prevent level busts. The other day I said "Climb to FL230" which was readback correctly, but FL320 was set in the MCP. Error message, inquire with crew, error fixed. Level bust prevented 10,000 feet below where it might have been an issue.

Anyway just a point to say, I don't think I've ever seen this radar warning about a selected level above your cleared level, when speaking about meeting ALT contraints. But I'm in EASA land. I can see the benefit of changing your MCP alt when approaching the waypoint to the next FMC alt, as long as it's all above your cleared level, but just a note from the ATC side that I don't often if ever see it happen. Unless your Mode-S output is deceiving us :)

[FullWings]

I would like you to imagine this kind of day out and offer your views on the situation particularly with regards to automation, trust in automation, monitoring, ATC.
Automation sometimes doesn’t play perfectly with procedure design and ATC intervention. STARs into KLAX come to mind. Trust, but verify as the old saying goes. I generally choose the method which generates the lowest workload, be it fully automatic, manual or anything in-between.

Monitoring is so important, across all timescales; FMAs all the way to re-routes. As soon as you start to deviate laterally or vertically from plan *anywhere*, it’s essential to project the flight path forward as far as is practicable. It may be of no consequence whatsoever but it is easy to paint yourself into a corner before realising it.

ATC bear a heavy burden when it comes to keeping the flight path of an aircraft safe, but as the guys at the front you have the ultimate responsibility and suffer the consequences of any mishaps in a very personal fashion...

[Roj approved]

Never mind, moving along. How do you (well familiarized) guys feel about using managed speed for deceleration and flap extension - if the ATC scenario allowed it?

I do it, hell, I even let the aircraft activate the App Phase itself by flying over the Pseudo WPT.

Luckily, for me, Australia is not overly busy, and the STAR’s have improved somewhat with many joining RNAV-X (RNP-AR’s). These have built in slow downs, so now, if there is no ATC intervention, the whole thing can be flown managed and flap taken on speed all the way to the threshold.

It’s a beautiful thing to behold.

What’s even more fun is to watch the F/O (or Check Capt) squirm because I haven’t played the FCU like Billy Joel the whole way down to follow the Managed DES and SPEED all the way to the Threshold, taking flap as required. 😂

But, when ATC get involved, a simple 3x calculation, and a liberal use of Speed Brake usually does the trick.

As to the OP’s question, SOP’s allow the dialling in of cleared ALT, if we are then instructed to turn off the STAR/level off, new HDG/ALT is to be entered on the FCU. (In this case, I would usually enquire if the ALT restriction still applies)

[Check Airman]

I generally choose the method which generates the lowest workload, be it fully automatic, manual or anything in-between.


I agree with this 100%

[tttoon]

FWIW, my company's version of the FCTM (B737 and 787) tells us to only select the next step down altitude in the MCP once you're sure the current constraint will be respected, either due to ALT HOLD or the altitude trend indicator. So in case of a "descend via" clearance, we're still supposed to set all stepdown altitudes in sequence. Same for climb restrictions.

[pineteam]

Is it common that the autoflight system will not comply with altitude constraints?
I’m just curious, I never flew Boeing, I would love to tho! On A320 no such restrictions, we always set the lowest altitude and it will comply with the altitude constraints. At least from my experience I never saw it failing to do so.

[Banana Joe]

It's down to the operator and we can set the lowest altitude. The FCTM calls it alternate MCP altitude setting technique. Just make sure to always remain in VNAV PTH or VNAV SPD.

[tttoon]

pineteam

No, I can't say I've seen any SRs about aircraft not respecting the VNAV constraints. I personally don't agree with the procedure, it adds workload and the potential for unwanted level-offs. Boeing only recommends the alternate procedure (setting the highest/lowest altitude) for closely spaced constraints. It's one of those "thats what the book says" things I guess.

[Superpilot]

Mistrust of automation is definitely more common amongst Boeing pilots. Historically speaking, quite understandable. Though Boeing have tried on the 787, seems type chiefs are just not interested in changing their old ways. Fly it like a tractor you will!

[TukwillaFlyboy]

Setting intermediate altitudes is a pain but its not because of distrust of automation.
Its about commonality of procedures across all approach types.
So long as non-precision approaches exist there is a place for a conservative approach.
Where I operate part of the problem has been ATC unwillingness to fully embrace RNP AR approaches.
When they were first introduced in OZ they had minima of 200’ !
They were trashed because to many operators wouldn’t or couldn’t use them and different types had different minima and increased ATC workload to apparently unacceptable levels.
Solution ? Get rid of them.
Plus ATC likes to keep the option of taking you off an approach on a heading.
Out of VNAV.
Setting intermediate altitude is cheap insurance.

[Check Airman]

FlightDetent

As it turns out, I had the chance to do a fully managed arrival today. With the speed managed, I got all the way to F2, then saw it was going to slow to ~160kt about 8nm from the runway. I guess it'd have been fine today, but in a normal traffic situation, it would have just messed up the approach controller's day.

It's a clever system, and I like it, but it isn't very practical for day to day use.

[FlightDetent]

I'd be interested to see which approach and arrival it was, PMs accepted..

The best description I have is it's not up to the task of achieving a meaningful speed reduction schedule. All winds and ISA dev typed in, etc etc...

[Check Airman]

KRDU 23R from the TAQLE1

[Roj approved]

Check Airman

This is my experience too, once F2 selected the speed drops too low, on some approaches that is the time I’ll select 160-180kts to avoid upsetting ATC. Some of the approach allow you select F2 later, or have 160kt restrictions further out, so it all works well. YBCG 14X, YBSU 13W

I think it does a great job, and it makes life very simple especially in marginal weather.