Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Managed descent, altitude constraints, radar headings

Tech Log The very best in practical technical discussion on the web

Managed descent, altitude constraints, radar headings

Old 12th Jun 2021, 16:22
  #1 (permalink)  
Thread Starter
 
Join Date: Jan 2013
Location: Anywhere
Posts: 79
Likes: 0
Received 0 Likes on 0 Posts
Managed descent, altitude constraints, radar headings

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!
MonarchOrBust is offline  
Old 12th Jun 2021, 16:46
  #2 (permalink)  
 
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 944
Likes: 0
Received 0 Likes on 0 Posts
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
pineteam is offline  
Old 12th Jun 2021, 17:59
  #3 (permalink)  
 
Join Date: Feb 2003
Location: Blue sky
Posts: 266
Received 6 Likes on 5 Posts
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...
BraceBrace is online now  
Old 12th Jun 2021, 18:07
  #4 (permalink)  

ECON cruise, LR cruise...
 
Join Date: Apr 2002
Location: MIRSI hold - give or take...
Age: 52
Posts: 567
Likes: 0
Received 0 Likes on 0 Posts
...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...
Empty Cruise is offline  
Old 12th Jun 2021, 18:25
  #5 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,509
Likes: 0
Received 0 Likes on 0 Posts
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.
Check Airman is online now  
Old 12th Jun 2021, 20:03
  #6 (permalink)  
 
Join Date: Jun 2021
Location: planet earth
Posts: 6
Likes: 0
Received 1 Like on 1 Post
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.

Last edited by gimbal error; 12th Jun 2021 at 20:49.
gimbal error is offline  
Old 13th Jun 2021, 04:23
  #7 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting not home
Age: 46
Posts: 4,302
Received 3 Likes on 3 Posts
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.

Originally Posted by gimbal_error
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.

Last edited by FlightDetent; 13th Jun 2021 at 05:35.
FlightDetent is offline  
Old 13th Jun 2021, 04:26
  #8 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting not home
Age: 46
Posts: 4,302
Received 3 Likes on 3 Posts
Originally Posted by Check Airman
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?
FlightDetent is offline  
Old 13th Jun 2021, 05:25
  #9 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,509
Likes: 0
Received 0 Likes on 0 Posts
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.
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.
Check Airman is online now  
Old 13th Jun 2021, 05:31
  #10 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting not home
Age: 46
Posts: 4,302
Received 3 Likes on 3 Posts
Originally Posted by Check Airman
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.
Departing from a field with stepped climb constraints, I do exactly that. Although it's not what you're saying, understood.
FlightDetent is offline  
Old 13th Jun 2021, 06:16
  #11 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,509
Likes: 0
Received 0 Likes on 0 Posts
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.
Check Airman is online now  
Old 13th Jun 2021, 06:25
  #12 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting not home
Age: 46
Posts: 4,302
Received 3 Likes on 3 Posts
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.
FlightDetent is offline  
Old 13th Jun 2021, 07:36
  #13 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,509
Likes: 0
Received 0 Likes on 0 Posts
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".
Check Airman is online now  
Old 13th Jun 2021, 08:49
  #14 (permalink)  
 
Join Date: Jun 2021
Location: planet earth
Posts: 6
Likes: 0
Received 1 Like on 1 Post
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.

Last edited by gimbal error; 13th Jun 2021 at 15:01.
gimbal error is offline  
Old 13th Jun 2021, 09:35
  #15 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting not home
Age: 46
Posts: 4,302
Received 3 Likes on 3 Posts
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?
FlightDetent is offline  
Old 13th Jun 2021, 14:33
  #16 (permalink)  
 
Join Date: Oct 2015
Location: 43N
Posts: 264
Likes: 0
Received 0 Likes on 0 Posts
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 is offline  
Old 13th Jun 2021, 14:42
  #17 (permalink)  
 
Join Date: Oct 2015
Location: 43N
Posts: 264
Likes: 0
Received 0 Likes on 0 Posts
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.
CaptainMongo is offline  
Old 13th Jun 2021, 14:45
  #18 (permalink)  
 
Join Date: Jun 2021
Location: planet earth
Posts: 6
Likes: 0
Received 1 Like on 1 Post
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.
gimbal error is offline  
Old 13th Jun 2021, 15:02
  #19 (permalink)  
 
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 944
Likes: 0
Received 0 Likes on 0 Posts
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.
pineteam is offline  
Old 13th Jun 2021, 16:03
  #20 (permalink)  
 
Join Date: Dec 2001
Location: GA, USA
Posts: 3,182
Likes: 0
Received 11 Likes on 8 Posts
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.
B2N2 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.