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Final approach speeds

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Final approach speeds

Old 14th Nov 2006, 22:08
  #61 (permalink)  
 
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Exclamation

When Mode S was introduced, I wondered how long it would be before we had the first ‘Why did you touch that button? event.

Operating in and out of LHR can be the most frustrating experience, those of us who have to do it often bear the scars. The issue of speed management on final approach is complex though, and we would be wise not to dismiss it lightly.

Finals 27R is not the M25, we don’t drop the clutch, shift up a gear and slow to 40 every time the cash-cow-cameras change their minds. Bear in mind that the aircraft in ‘the tube’ are all different. Some are heavy, some light, some with GS mini function, some like the 757 might be doing 90kts inside 4, some have different high lift configuration, some need extra drag, some might need that last few moments of low drag to avoid a low fuel event.

Your mode S updates once a scan, and you might catch a 747 whilst he’s experiencing a 20kt gust. Because of inertia, the aircraft stays where it was whilst the ASI reads +20kts. That won’t happen on a 320, but his ASI will vary according to GS mini when managed speed is selected for landing.

If that sounds confusing, then good. It shows that this business is a panoply of operational problems and compromises. No-one operates in and out of Heathrow with intent to bust the limits. We try our very best to play the hand we’re dealt.

If the beancounters have just leant on you to pack ‘em in tighter, tell them from me to poke off.

If we wind the spring at LHR any tighter, someone’s going to get hurt.
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Old 14th Nov 2006, 22:11
  #62 (permalink)  

 
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Originally Posted by Gonzo View Post
Some assumptions on this thread are worrying.
Porco Rosso,
Not sure what you guys have been told, but this is certainly not the case. The rules have been changed so as to, in effect, 'legalise' the situations where FIN has aimed for 3 and got anywhere between 2.5 and 3. The inbound spacing to LL will still be 3 miles, whereas separation can now legally be anything down to 2.5 miles. The rules on when we adopt 2.5 miles spacing have not changed.
Gonzo, this has been sold to us as a change in procedure partly to tie up with what actually happens in practice but also to increase the envelope when 2.5nm can be used.

Take a look at the opening paragraph of our SI if you can get hold of it.

As for the tail wagging the dog. I don't try and do 2.5nm, or even 3nm spacing, for fun. I do it because that is what is required to to keep the airlines happy at a capacity constrained airport.

If one part of the airline industry is demanding maximum landing rate every hour of the day and another part of the same industry is saying we can't fly the required profile then the airlines need to sit down and agree exactly what is acceptable to them and what isn't then tell us in a co-ordinated fashion.
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Old 14th Nov 2006, 23:08
  #63 (permalink)  
 
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There's no reason why 99% of the aircraft going into Heathrow can't maintain 160 to 4d and still meet the stabilised by 1000' radio criteria. It really irks me when I see people reluctant to use ALL available means, be it flight controls (yes, speed brakes are a flight control) or gear to comply with ATC speed requests, especially in places like Heathrow where it is critical. Flying the aircraft in an efficient and economic manner is not the name of the game on finals to Heathrow. So get over yourself and use the whatever it takes to comply. With the Airbus, configured to CONF 3, Gear Down, 160 Kts selected, manage speed inside 4.5d, take CONF Full and all is well by 1000' radio every time. There is no excuse. The only way you won't be stable by 1000' radio is if you are a regular Chuck Yeager doing a glide approach who can't handle the shame of having the gear out a few miles earlier than he would like or god forbid the speed brakes.
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Old 15th Nov 2006, 04:37
  #64 (permalink)  
 
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Actually, Phoenix, 'tis the Commanders choice, whether he wants to comply...or not.
Of course, if he can not (or will not) and can get a word in edgewise (somethimes difficult) he absolutely should, no doubt about it.
It is the controllers job to provide the separation, plain and simple, anyway he can.
IF speed doesn't do it, then sending an aeroplane around from time to time is certainly within his/her perogative...as it should be.
You must understand that certain airlines have rather rigid standard procedures, and especially if a (for example) new First Officer is being trained, the line training Captain is going to darn well see to it that these SOP's are complied with.
If the price is going around from time to time, or holding a bit longer, so be it.
And speaking of going around, this may well only affect a few, who continually plan to uplift absolute minimum fuel at departure, thereby possibly embarassing themselves once they arrive in the London TMA.
For these, I can only say...its your own damn fault.
Tough beans.

120.4, don't lose your rag over this whole affair, just send the malcontents around from time to time, and ignore the complaints.
Hey, the young co-jocks need the flying time anyway.

Last edited by 411A; 15th Nov 2006 at 05:07.
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Old 15th Nov 2006, 08:39
  #65 (permalink)  
 
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Snoop

'tis the Commanders choice, whether he wants to comply...or not.
In itself that statement is true. Commanders have the choice to ignore (or not) ATC instructions at any time. Whether this is a wise thing to do when those instructions are for the maintenance of separation is quite another matter. If ATC say "Turn right heading 300 degrees, descend 3,000 feet" and the Commander decides that he'd rather go left and climb to 5,000' and that brings him into direct conflict with another aircraft, then he'd better start getting ready for the inquiry. And obtain his own tea and biscuits.

I think PhoenixRising has said it all in a concise manner a few posts ago.
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Old 15th Nov 2006, 08:53
  #66 (permalink)  
 
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Airbus Unplugged

A quick query as you have me confused; I hope I do not confuse you with the first paragraph of my query due to the wording

Our Mode S shows the IAS that you have selected. Obviously as you slow down with inertia, the IAS in our Mode S will tick down til it gets to the required setting (much the same way as when we tell you to fly a heading.... you select the heading but our mode S follows your compass round until it hits the requested heading).

I was of the opinion that a gust of wind as you mentioned would not change the IAS reading, it merely changes your True Air Speed and ground speed, therefore, we can tell if you are at 160 by 4 dme because that is what your IAS readout should say. If you are established at 160kts and you experience a 20kt gust, does this cause the IAS to change??

Surely if that is the case, then when we ask you to do a set speed when you are farther out i.e. 290kts surely your mode S readout would show us what you were doing with regards to the wind i.e. if you had a 50kt tail wind, it would show up on our radar as speed of 340kts.

Just wondering really, because this does not happen with mode S.. we can see what (IAS) speed you are flying at that point in time (or radar update point), as well as the ground speed, which is the resolution of IAS to TAS to GS. Wind variations do not show up on the IAS part of our mode S readout.
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Old 15th Nov 2006, 09:05
  #67 (permalink)  
 
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Originally Posted by anotherthing View Post
I was of the opinion that a gust of wind as you mentioned would not change the IAS reading, it merely changes your True Air Speed and ground speed, therefore, we can tell if you are at 160 by 4 dme because that is what your IAS readout should say. If you are established at 160kts and you experience a 20kt gust, does this cause the IAS to change??
In the 744 we are not even presented with TAS information, only IAS. If we are established at 160kts and experience a 20kt +ve gust then yes, the IAS will rocket up to 180kts, then back down to 160kts when the gust passes. I'm not sure I understand what information your mode S readout is presenting you with. Is it the target speed we have selected (but not necessarily yet achieved) or is it the instantaneour IAS the aircraft is currently at?
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Old 15th Nov 2006, 09:27
  #68 (permalink)  
 
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A couple of months ago on final app in BRU we catched up a plane who was 20kts slower than instructed. The controller told him: " ... go around, I will vector you again with more space behind you"
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Old 15th Nov 2006, 09:51
  #69 (permalink)  
 
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Now that IS tail wagging dog!
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Old 15th Nov 2006, 09:51
  #70 (permalink)  
 
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CM: it's instantaneous IAS as reported by mode S from that particular radar sweep, not the target IAS. This is as opposed to selected flight level which is the SFL from your MCP. http://www.levelbust.com/articles/mode_s.htm has some pertinent info.

@.4 if you catch the lack of speed compliance early enough, sometimes a quick 'xxx123 report your speed' is enough. Responses (when supposed to be at 180 and clearly going slower) have varied from 'xxx123 one-eight- er... one seven, oh we're one sixty' to the blatant 'xxx123 we're at one-eighty, and we have a problem with one of our airspeed indicators'. <Pause> . 'xxx123....Roger'.

As stated by others, different speed requirements will be accommodated, however we need to know about it first. Otherwise, the tight margins can be eroded very quickly.

Cheers W.E.
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Old 15th Nov 2006, 10:31
  #71 (permalink)  
 
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I agree that speed control is vital in busy TMA's.When VMC,you can forego the profile to get the target speed.A lot of todays pilots dont know how to do this because:
a)they're SOP- fixated
b)they cant fly without an AP
c)they cant re-programme the MCP in a timely fashion to ensure speed gets priority over profile(thus keeping AP engaged)

Over-reliance on automation and SOP-fixation in busy TMA's lead to screw-ups.Examples:
a)You hear inexperienced pilots asking busy TMA's for descent because their VNAV profile is making them all panicky.ATC tells you when to descend!
b)Pilots ignoring the last assigned speed because their SOP says that they should be at some other speed
c)Pilots taking off with incorrect lateral nav data(probably after a late rwy/SID change)and blithely selecting LNAV and engaging the AP and watching the a/c turn the wrong goddamn way..they dont know anything else but the magenta track and so thats what they do.
d)Pilots selecting VNAV and then watching the aircraft level off at 3000' when you've been cleared to 5000'.
e)Pilots following a 757 3 behind and not doing their own vortex separation(keep high)..they cant fly without AP so the aircraft maintains glide and flies right into the wake.

If the only way to control speed is extra drag then use it as Phoenix suggested.Good God we can take the gear at 20 miles if we have to but its lousy airmanship.Speedbrake is ineffective at low speeds and is often limited by flap setting anyways.

If IMC,then profile is as critical as speed control and you've gotta do what it takes.
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Old 15th Nov 2006, 10:47
  #72 (permalink)  
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It seems to me that we are getting sidetracked from the original post - and I am guilty of that too.

It would appear that BA SOPs conflict with 160 to 4. This is an issue for BA to sort out, not ATC. If it requires 170 to 5 or whatever, then BA should push for it - moaning here will not do it. The rest of us can cope. In any case even an instant speed reduction from 160k to 150k at 5d instead of 4D makes, I think, a difference of about 200ft in separation - which is lost in the mists of Vref spread anyway.

The major issue is total non-compliance. Short of actually executing pilots like 411A, the only solution is for ATC to begin formal reporting. The on-board data recorders will show the companies whether it was so.
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Old 15th Nov 2006, 12:18
  #73 (permalink)  
 
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Originally Posted by BOAC View Post
... In any case even an instant speed reduction from 160k to 150k at 5d instead of 4D makes, I think, a difference of about 200ft in separation ...
I beg to differ, BOAC, by my calculations:

"Slow" Aircraft A is 150kts at 5DME and, at that speed in still air (2.5nm per minute) will take 24 secs to reach 4DME.

Aircraft B behind, travelling at 160kts will travel 1.067nm in the same 24 secs.

The reduced separation of 0.067nm is approximately 400 feet not 200 feet?

Your 200 feet would I think be the correct answer assuming a linear speed reduction by Aircraft A from 160 to 150kts between 5DME and 4DME not an instantaneous one at 5DME.

I accept your 'instant speed reduction' is not real, but I suggest a single nautical mile of the final approach i.e. 24 seconds is not a very long time period to be analysing as fully "containing" or bounding the problem scenario. I am NOT a PP so I could be very wrong when I say that I guess the problem begins earlier. If that is the case, multiples of 400 feet every 24 secs soon eats into safe separation even if everyone else in the sky has nailed it as instructed.

I have treble-checked my maths and have hit Submit and now stand meekly to be corrected
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Old 15th Nov 2006, 12:45
  #74 (permalink)  
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Dunces cap on and standing in the corner!
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Old 15th Nov 2006, 14:54
  #75 (permalink)  
 
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Surely we're dealing with horizontal separation not vertical, which would only be accurate to the degree stated if both were on an ILS hugging the glide, LHR still has NPA's.

MATS pt 1 allows for a reduction in separation inside 4 miles, until then comply with ATC instructions or advise ATC that you cannot and offer what you can do. IFR inside CAS, nuff said.

IN
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Old 15th Nov 2006, 17:45
  #76 (permalink)  
 
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411A;

You are letting yourself down again; embarrass has two 'r's and two 's's.

Mind you, I suspect that you have never been embarrassed since you were 18 months old!
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Old 15th Nov 2006, 19:05
  #77 (permalink)  
 
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Honesty hat on as a 737 BA driver (So Gatwick - But the same issues apply)

Just for understanding purposes, the 1000' 'gate' applies to radio altitude, not aal - Important where it comes to 08R at LGW as Russ Hill moves the goal post.

To see the variation in target speeds on our fleet let me give some examples -A 'heavy' 737-400 has a Vref of 138Kt, so we aim to fly 143Kt. 17Kt loss - No problem. A 'light' 737-500 (look out for the inbound LUX and HME services) have Vrefs down to 108Kt, aiming to fly 113kt - 47 Kt loss which is quite a problem.

On the fleet we have quite a range of experience, the newbies are trained to slow by 5. I do try to encourage people to go further before slowing, but they don't always feel comfortable doing it. Thing is, using common sense you can judge when to slow down to achieve the 1000' radio altitude gate, and most of the time on 26L you can go all the way to 4d. On 08R, you can't do it in a 737-5, 737-3 or even sometimes in a 737-4 due to Russ Hill. But not everyone thinks about the goal - Just the fleet worst case hence they slow down early!

Now this is a BA type problem. There was no problem going back 5 years on the 737, as we had to be stable by 800' Radio but things changed and that backward step prevented us fitting in with ATC. But then we fitted in with BA and that was deemed to be a good thing.

Hope that helps - I do tend to ask for 170/5 coz it does 2 things (we meet the speed that is agreed and we keep the gear up significantly longer) but a few of my colleagues don't seem to see the benefit. Keep the pressure on and I am sure that our management will see fit to come up with a plan that keeps the traffic flowing. You have to sell it though - If they can come up with a plan, just think they might get some extra slots due to greater efficiency. With that carrot, I'm sure they will talk....
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Old 15th Nov 2006, 20:22
  #78 (permalink)  
 
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[off topic] At gatwick, I do sometimes use 170kts tactically to fine tune the spacing. I guess that's more benificial to 'heavy' 734's? [/off topic]
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Old 15th Nov 2006, 22:50
  #79 (permalink)  
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Are there any typical Heathrow types other than the B757 that would have difficulty with 170kts to 5?

I don't see how we can allow the situation to continue where aircrew are being asked to operate outside SOPs and so it seems to me that we need to consider officially raising the possibility of a change in the ATC requirement. I will raise it with TC ops if I get enough of an indication here that 170 to 5 would be more suitable all-round. Of course, just as now, exceptions would still be okay provided we are told before the base turn.

I would still like to understand why the aircrew of a competent, British B744 operator would choose to be at an IAS of 145kts at 6nm from touchdown in normal conditions, having accepted 160kts to 4d. That is not satisfactory.

.4
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Old 15th Nov 2006, 23:06
  #80 (permalink)  
 
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Originally Posted by 120.4 View Post
I would still like to understand why the aircrew of a competent, British B744 operator would choose to be at an IAS of 145kts at 6nm from touchdown in normal conditions, having accepted 160kts to 4d. That is not satisfactory.
.4
If its a BA 744 then one would have to question the competence. 145kts in a 744 is roughly final approach speed and at typical landing weights would require gear down and landing flap selected. Short of flying the ILS with an enormous tailwind I can't think of any reason to be fully confgured and slow at 6d. If it was BA then please write to the company and a reminder will be issued to crews.
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