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time at an ATC directed way point

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time at an ATC directed way point

Old 31st Oct 2014, 23:02
  #21 (permalink)  
Join Date: Mar 2002
Location: Seat 0A
Posts: 8,129
The problem with speed differences come from different crews/aircraft choosing to lose time in different ways - if the front one reefs it right back early the back can close up remarkably quickly.
Seen that a few times. There are a couple of ways to skin the cat; one of them results in exactly that. Tigermoth cruise speed and Concorde shuttle descent speed...

Can we program Maestro to give us another 15, 20 mins to slow down
Agree. In the "old" days when humans did it, we got our FF time nice and early (even in the climb!) and didn't need to climb to the moon, only to descend back down almost straight away. Now the machine's doing it, we get our FF time much later which requires more drastic action. That said, over here the ATCs are getting adept at dropping "hints" about how much time we'll have to lose instead of just saying "reduce by 0.05", which in the big scheme of things has very little effect at all.
Capn Bloggs is offline  
Old 1st Nov 2014, 04:37
  #22 (permalink)  
Join Date: Aug 2007
Location: Running up that hill
Posts: 308
Oakape interesting, thanks foe that. I had assumed (i know) that you just fed in the time and the machine took care of everything.

For me, having a required time at a pre-descent point & then a fixed speed schedule for descent would be the easiest way of ensuring everyone gets where they are needed at the correct time. Any corrections required due to wind changes on descent could then be dealt with by ATC speed control or vectoring.
A very similar idea has been floated. Simply move the fix much further out, i.e. prior to descent point. The descent phase then becomes mush easier for us as everyone is doing the same speed on descent (just like the old days pre FF's). The downside is that it gives you a lot less time to achieve the requires time.

Capn Bloggs and hung start when we went to MAESTRO in PH a conscious decision was taken not to issue FF times until with the inner sectors (134.2/133.8 from the north, 135.8/118.2 from the east).

MAESTRO will recalculate the entire sequence every time a single piece of information is changed (aircraft estimates, RWY config, acceptance rate). For a RWY change this is a massive advantage over the manual system, but other time its can be a disadvantage.

MAESTRO starts sequencing (i think) at least two hours out, but it will be in a state of flux as estimates change and short leg flights depart etc. The closer you get to arriving the more stable the times become. It was decided that prior to the inner sectors, rather than issuing a time that will in all likelihood change more than once, we would give speed reduction based on the current MAESTRO time. I can't remember the exact values but it's something like up to 5 minutes - no reduction, 5-10 reduce by M0.05, grater than 10 reduce by M0.05 or greater, expect an X minutes delay.

One side advantage of this is that two aircraft in trail given a delay will both reduce by the same amount, reducing the different profile/speed issue. None of these procedures are set in stone however, and can be altered if that's what industry wants.

Its the same reason we changed to giving a hold departure time rather than 'depart the hold to make the fix time'. That way between the holding point and the fix everybody will be doing the same speed.

With regard to the speeding up to 250 after the fix, I was very surprised that jets would do less than 250 prior. I was expecting a 250 knot descent and than if that was not enough a request for vectors/holding. I didn't even know a jet could do 210 on descent, I was always taught 250 was a minimum we could assign, if we had really messed up we could ask nicely for 240 or maybe 230.
Nautilus Blue is offline  
Old 1st Nov 2014, 05:10
  #23 (permalink)  
Join Date: May 2007
Location: Western Pacific
Posts: 721
With regard to the speeding up to 250 after the fix, I was very surprised that jets would do less than 250 prior. I was expecting a 250 knot descent and than if that was not enough a request for vectors/holding. I didn't even know a jet could do 210 on descent, I was always taught 250 was a minimum we could assign, if we had really messed up we could ask nicely for 240 or maybe 230.
The minimum speed depends on altitude & weight, along with type to a lesser extent. Generally, the lower you get the slower you can go - down to minimum clean speed, which is around 200-210 kts at typical landing weights on the NG. (taking flaps will get you slower, but can't be used above FL200 & that is the last thing we want to do anyway!) Generally you are light when arriving & in an NG, light enough to get back to 210-220 kts somewhere around FL300. Above FL300 would require a bit more speed. It depends a little on the particular pilot's (read captain's) pucker factor or simply personal preference, and also on turbulence, etc. The B777 wasn't too bad either if I remember correctly, with slightly higher speeds, maybe 5 or 10 kts more.

Constant speed descents are easier for the FMC to calculate & fly in VNAV, which is the way the boss likes us to fly it. However, it can handle one or two speed reductions, preferably over waypoints (easier to program). Once you get speed increases or vectoring, you are off the 'path' & then it is back to manual calculations. It can be done & is really no bother to most, it just offends our sense of economy & passenger comfort.

Once everyone gets their heads around what has to be done to move large volumes of traffic, then you will get a better response to any restrictions & less complaints. Guys are still trying to hang onto economy. Perhaps a couple of months in Dubai would educate them & they would see that it is still pretty good in this neck of the woods.
Oakape is offline  
Old 1st Nov 2014, 05:33
  #24 (permalink)  
Join Date: May 2009
Location: YMML
Posts: 1,721
In the good ol' days the flow was the only one doing the times - he'd do all the fiddling of figures and we'd just pass it on. Things were set in concrete early. Now there are many fingers in the pie and the times aren't set in concrete until much later - the dilemma for controllers is give a time too early and it's likely to change several times, frustrating and time wasting for everyone.

Maestro is another thing for us to monitor so if we're busy separating traffic we might not look at it for a bit and not notice you've gone from no delay to 6 minutes - we don't get directed warnings, it just happens.

We know you like times early and I'll try to slow you early when I can but that relies on me even noticing you before you're handed off to me - when it's busy that often gets missed because it's low priority.

Re. efficiency of constant profile descents and such - I cack myself laughing every time I read of the latest scheme proposed to save fuel. You can achieve whatever you want when you're the only aircraft in the sky but as you say, the more aircraft the less likely that is to happen.
le Pingouin is offline  

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