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flatfour
23rd Apr 2008, 07:29
In order to mitigate the noise of arriving aircraft it has been suggested that a steeper glide slope could be used. What would be the advantages and disadvantages of increasing the slope to 4 degrees ? I should welcome professional pilots views on this.

5150
23rd Apr 2008, 07:35
I think you'll find a number of modern jets will struggle to achieve stability on a 4 degree glideslope.

HEATHROW DIRECTOR
23rd Apr 2008, 07:40
Doesn't London City have a 6 degree slope? Presumably the types of aircraft flying there are designed to accommodate that?

Tail-take-off
23rd Apr 2008, 07:43
Yes it would be nice & quiet under the approach chart.

Not so good for those living near the over run area though with all the noise of aircraft running off the end of the runway.

On a serious note 4 degrees is a bit too steep for most medium to large jets. I'm sure that lots of people can point you in the direction of statistics regarding the merits of stable approaches. One of the requirements being no more than 1000 fpm rate of descent. Sometimes this is not possible with slopes of up to 3.5 degrees so 4 degrees would be a non starter.

However there are a number of turbo props & a very small number of jets that are designed to operate into city centre airports where noise is super critical that can do 4 degrees & more.

Perhaps with time the normal (3 degree) glide slope will become steeper, as aircraft design evolves, but at the moment the safety issue out weighs the noise problems.

Icing
23rd Apr 2008, 07:51
Marseille runway 31R has a 4 degree glide slope and the 737 doesn't have a problem with that as long as you configure nice and early. The majority of aircraft are not certified though to do autolands from approaches steeper than approximately 3,25 degrees. So a 4 degree slope might not be very practical for larger airports like LHR, LGW en STN since they operate quite regularly to CAT 3.

BOAC
23rd Apr 2008, 07:52
Not only possible but not unknown: 4.46 deg at CMF for example. Cannot remember MRS 32 but it is steep. Certainly 3.5 deg would be fine. Just requires a modified technique.

777AV8R
23rd Apr 2008, 07:54
Yup, a 4 degree slope would not be workable on a 777. Maximum certified autoland is 3.25 degrees.

richarjm
23rd Apr 2008, 07:56
I regularly fly a 737-800 into Marseilles on a 4 degree glide. The ROD can sit near or even over 1000ft/min but so long as you brief that fact and both pilots are aware, it presents no problems other than a slightly more pronounced flare. Glasgow Prestwick in Scotland has a 3.5 degree glide which we use happily as do the large number of 747-400 freighters that operate there.
Basically where surrounding terrain makes it necessary it can absolutely be done and in a safe stable manner.
Best,
richarjm
Edited to add that as people have said above since i started writing, Auto the pilot is not approved to land after one of these approaches.

Variatie
23rd Apr 2008, 07:59
Yes, but only a limited number of aircraft can maintain a steady descent-rate on this glideslope. (6° I mean, not 4°) And even then, most companies (if not all) will only allow the Captain to execute the approach.

The advantage/disadvantage of a 4°-glideslope lies in the powerrequirement. As was already mentioned, we would need less enginethrust to maintain a stable speed during final descent. Less enginethrust equals less engine-noise. However, that is also the risk (the thrust, not the noise).

As the descentangle/glideslope increases, the component of airplane weight along the direction of travel increases also. This causes the need for less enginethrust. (E.g. a rock. If you drop a rock of a bridge, the component of its weight is completely along its direction of travel - vertical. It does not need thrust to accelerate.)

Since there is reduced "excess"-thrust (thrust above idle, in this case) it will be more difficult to control/eliminate any excess speed. Larger, heavier airplanes might not be able to reduce speed with normal means at all.

I do agree, approaches in Marseille are usually safe and stable. However, the margin of error (consider tailwind on final!) is smaller.

DB6
23rd Apr 2008, 08:07
What's the point? Isn't the climbout path where most of the noise is? Quite apart from the fact that people that choose to live near airports should have to accept the noise..........:E.

BALLSOUT
23rd Apr 2008, 08:13
Yes, as others have posted. It can and does work in some instances, but is/would only be cat1. It would also need more seperation between arriving aircraft to allow them to slow up and configure for it. I expect there would also be an increase in missed approaches.

richatom
23rd Apr 2008, 08:16
I regularly fly a 737-800 into Marseilles on a 4 degree glide.


Just out of interest are RyanAir now cleared to do the CDA approach to 31R?

Admiral346
23rd Apr 2008, 08:38
so what really happens on a 4° slope?

You have to start configuring much earlier, like it has been said, in Marseille you should start the ILS with flaps 20°, or you won't stand a chance (that is in the CRJ -700-900). On a 3° glide I can delay flaps 20 to around 2000' AGL if not speedrestricted by ATC. I also can delay the gear.

On modern aircraft the majotity of the noise is created by interference of slipstream around gear/flaps. The engines are at idle anyways and only give off a slight hiss, until - yes, just until - I have to start stabilising my approach by getting flaps and gear down and increasing engine power. Then the noise really starts...

So what do you gain by shifting to a 4° glide? - In theory, aircraft would fly about 30% higher off the ground, so at 10 miles 4000 iso 3000 feet - that is a gain, no doubt, and a big noise reduction.
Now at 6 miles out 2600 iso 2000 feet, still some advantage...
At 3 nm 1300 iso 1000 feet - not much difference.

Unfortunatly it won't really work that way - You have to get the flaps out at 10 nm, increasing the noise (remember, you don't fly slower, you just need more drag to maintain speed), somewhere between 10 and 7 nm you would need the gear to go down (on a CRJ - on an A330 starting down with anything less then gear down and flaps 2 would lead to a goaround). Final configuration must be achieved earlier to get down to Vapp, thereby increasing noise levels...

I think if a 4° slope wouldn't increase noise levels, they ought to be about the same, with a huge downside on safety - less stable approaches, higher rates of descent,...

In my opinion. not an option at all...

Nic

edit:
PS: The most silent approaches can be achieved at airports with little or no traffic, where ATC doesn't get in your way.
You just glide it down, and set it up to have the right speed and little flap hitting the glide at the descent point, take it down the ILS and drop everything at 1800 to 1500 feet AGL, to be established at 1000' exactly, not moving the throttles out of idle all the way...

Most satisfying, when done right...

Nic

richarjm
23rd Apr 2008, 08:39
I'm off work today but if I remember I'll check our brief tomorrow and let you know.

No RYR for me
23rd Apr 2008, 08:53
Auto the pilot is not approved to land after one of these approaches. Classic! I remember that one :D

Dan D'air
23rd Apr 2008, 09:12
Anyone else been to Chambery lately? That's always fun!!

Empty Cruise
23rd Apr 2008, 09:19
Not so good for those living near the over run area though with all the noise of aircraft running off the end of the runway....

Funny, the last time I looked at anything relating to performance, you definitly got a landing dist/mass credit from having a steeper approach angle... but maybe they have found a way to eliminate that as well? ;)

Re. 777 - so you cannot do an autoland, fair'nuf - how about max certified approach angle? Might be a different story.

5150
23rd Apr 2008, 09:26
HD

London City is 5.5 degree (or was the last time I went in there a few years ago!)

ZAGORFLY
23rd Apr 2008, 09:35
yes the B 146 does the job

http://www.youtube.com/watch?v=KOAkZrC87Mc

Kerosene Kraut
23rd Apr 2008, 09:35
Point is you will have to add some safety margin making the approach even steeper: Like in LCY it's 5.5 degrees plus 2 = 7.5 degrees that you need to be certified for. If you aim at 4 for noise abatement you'll end up close to six in real life certification. That is way steeper than many a/c can handle. There where quite a few mods done to the A318s computers, avionics, callouts, trim, flaps and speedbrakes in order to get it certified for LCY ops.

captjns
23rd Apr 2008, 09:43
http://www.airnav.com/airport/VNY/ils/16R

http://204.108.4.16/d-tpp/0804/00552I16R.PDF

Van Nuys, California RWY 16R

3.9 degree G/P

Vref is lower on the 727 and 757... so not a big deal. The 737-800, on the other hand, with higher a Vref requires ealier configuration. To add to the fun there is sometimes a tailwind at the onset shifting to a 0 wind about 500 AGL.

Tail-take-off
23rd Apr 2008, 10:47
Not so good for those living near the over run area though with all the noise of aircraft running off the end of the runway. ...

Funny, the last time I looked at anything relating to performance, you definitly got a landing dist/mass credit from having a steeper approach angle

Empty cruise, I knew someone would bite:ok:.

What I was refering to was comming screaming in down the steep slope, not configuring early enough & being too fast at the threshold. I dont think you get any performance credit for that:=.

Bushfiva
23rd Apr 2008, 10:55
On modern aircraft the majotity of the noise is created by interference of slipstream around gear/flaps

I think I'm about to ask something numbingly stupid, but that's what I'm here for.

If gear noise is that noticeable, wouldn't it be reasonable to consider aerodynamically-shaped strut components in the design phase? Having worked in a different field with drag (simplifying, drag = noise), relatively small engineering changes can have large positive effects.

Kerosene Kraut
23rd Apr 2008, 11:01
This is what they do already. They even close parts of the gear doors again after the gear has moved down to keep the noise lower.

wobble2plank
23rd Apr 2008, 11:02
I seem to remember the 318 LCY requires the speedbrake to be fully deployed and the gear down prior to the commencement of the approach with the spoilers being used as drag/dump devices in a similar way to the Tristar.

The approach is flown to a double flare with the first being at about 300' to achieve a 'normal' flare at the normal height. (doing this from distant memory so the figures could well be wrong!)

Should be a fun approach after a 2 man night trans atlantic crossing from NY!!!! :eek:

The 319 into MRS is no problem at all, 4 deg slope gives you about 1000' per min at the threshold, a gentle progressive flare from 50' is no difficulty.

Please don't 'slipstream' the gear!!!! On a light 319 it is sometimes the only way I can slow the bugger down.

ComJam
23rd Apr 2008, 11:02
London City is still a 5.5 degree slope. I think i'm right in saying that someone has recently started operating Airbus 318(?) into there. Must be interesting the first time you do it one of those, it looks odd enough in KingAir nevermind anything bigger! :}

As for the 777 and a 4 degree slope being unworkable because the autoland is only certified to 3.25 degrees......can't you hand fly that a/c and actually land it yourself or am I missing something :ugh:

captjns
23rd Apr 2008, 11:14
You can hand fly or use the coupler for an ILS with a steep glide slope... as long as the actual landing is accomplished by the flying pilot.

Norman Stanley Fletcher
23rd Apr 2008, 11:32
At easyJet we have recently changed our 'stabilised approach criteria' to reflect the use of higher than 3° glideslopes. In the past it was only permitted to have <1000 fpm rod under all circumstances below 1000'. That has now changed and you can add 150fpm for each 0.5° extra on the glideslope. So at MRS where the glideslope is 4°, you can now accept anything less than 1300fpm as being 'stable'. Obviously you adjust the flare accordingly, but it has taken a lot of the pressure out of these types of approaches and seems a sensible tweak to the rules. I am a previous user of the 5.5° glideslope at LCY, and again as long as you have had the proper training and observed sectors, it is no problem if you follow the correct techniques.

planecrazi
23rd Apr 2008, 12:10
Airbus limits autoland to 3.15 degrees for A340/A330, however, we do a VOR approach into Kathmandu at 5.8 degress(yes, minus 5.8 degress), at 10 DME, 9500ft and a 4 DME we reduce to 3.5 degrees. We start off at 138 IAS, and sometimes have it increase to 170 on the way down in an Airbus A330. This is not easy, but lots of things are considered, but I would hate to try it on an ILS, as there is no reduction in angle to slow down.

Pugilistic Animus
23rd Apr 2008, 12:41
doesn't the shuttle approach on a 25 deg g/s?--thats some energy management---especially considering that most come within +/- 3 knots on the 205 knot Vref and hit the TDZ within 250 ft:eek:

AMEX
23rd Apr 2008, 12:46
As for the 777 and a 4 degree slope being unworkable because the autoland is only certified to 3.25 degrees......can't you hand fly that a/c and actually land it yourself or am I missing something

I think what people mean is that normal Cat III A,B ops is done with the autopilot engaged all the way to roll out (And I am talking in actual condition, not just for the Autoland practice requirement). So if the A/P is not certified then you lose your CAT III ability.

Mike734us
23rd Apr 2008, 17:47
As RNP becomes more widespread a variety of glide slopes could be implemented. Different aircraft could be certified for different glide slopes.

http://en.wikipedia.org/wiki/Required_Navigation_Performance

ManaAdaSystem
23rd Apr 2008, 19:24
The short answer:

Is it possible? Yes.

Is it practical? No.

tartare
23rd Apr 2008, 20:57
Exactly.
20 degrees plus - now that's a man's glide slope.
It took someone of the calibre of Mr Armstrong to sort that one out.
What a ride that would be...

Two's in
23rd Apr 2008, 22:25
In order to mitigate the noise of arriving aircraft

I think you will find that the low risk, optimized flight safety option is called installing double glazing if you live near an airport. Get the Government to change the way thousands of aircraft operate or splash out on a few home improvement? Oooh, I know this one....

FougaMagister
23rd Apr 2008, 23:49
I agree with most previous posts. The advantage in terms of noise abatement of a 4 degree glideslope would be minimal - and might lead to an increase in go-arounds.

Berlin/Tempelhof (THF/EDDI) has non-standard slopes too;
ILS 27L: 3.50 degrees / 6.1%, DH (Cat B a/c) 265', RVR 650m
NDB 27L: 3.50 degrees / 6.1%, MDH (Cat B a/c) 757', RVR 1,400m
VOR 27R: 3.70 degrees / 6.5%, MDH (Cat B a/c) 677', RVR 3,000m

The high DH/MDH/RVR values reflect the higher RoD. Runway 27L is 1,840m, 27R is 2,094m.

No big deal on an ATR72, although medium/heavy jets (737-300/700, A320 etc.) have been known to land there sometimes :ok: http://www.airliners.net/photo/LTU---Lufttransport-Unternehmen/Airbus-A330-223/1263866&photo_nr=4&prev_id=1264091&next_id=1263834

Cheers :cool:

Bally Heck
24th Apr 2008, 01:27
Best to do what they do already and, if it's a steeper than 3.5 degree slope make it a non precision! How much easier is an NDB or VOR approach than a really hard ILS?

Mad (Flt) Scientist
24th Apr 2008, 03:46
Point is you will have to add some safety margin making the approach even steeper: Like in LCY it's 5.5 degrees plus 2 = 7.5 degrees that you need to be certified for. If you aim at 4 for noise abatement you'll end up close to six in real life certification. That is way steeper than many a/c can handle. There where quite a few mods done to the A318s computers, avionics, callouts, trim, flaps and speedbrakes in order to get it certified for LCY ops.

That bit in bold isn't quite right. As the certification rules are currently applied (and there is some variability between jurisdictions, and some of the rules are evolving as new aircraft apply) the rules are:

up to 3.5 degrees - nothing special required, standard certification applies (i.e. 3 deg G/S)

between 3.5 and 4.5 (4.49999999 if you like) - additional requirements for autopilot etc.; no additional requirements for SubPart B (i.e. performance and handling)

4.5 and above - considered "Steep Approach" - additional SubPart B requirements added, including the "+2 degrees" abuse case.

So certifying a 4 degree approach would typically require additional avionics work but generally not much in the way of handling and perf tests, and certainly not the 2 degree abuse case. (That's pretty much the TCCA/EASA approach right now, with the FAA not too dissimilar)

Kerosene Kraut
24th Apr 2008, 08:17
Thanks Maddie,
didn't know about that mid-steep category.
Kraut

ComJam
24th Apr 2008, 12:33
I think what people mean is that normal Cat III A,B ops is done with the autopilot engaged all the way to roll out (And I am talking in actual condition, not just for the Autoland practice requirement). So if the A/P is not certified then you lose your CAT III ability.

You can't have a CAT III system with a G/S angle in excess of 3 degrees anyway...can you?

411A
24th Apr 2008, 13:32
You can't have a CAT III system with a G/S angle in excess of 3 degrees anyway...can you?

A common mis-conception.
And, yes it is possible, with specific aircraft, with full automatic approach/land capabilities, designed long ago.


I seem to remember the 318 LCY requires the speedbrake to be fully deployed and the gear down prior to the commencement of the approach with the spoilers being used as drag/dump devices in a similar way to the Tristar.


Imagine that...how ironic.:}

Stop Stop Stop
24th Apr 2008, 16:17
I seem to recall that last time I was in Marseille, I taxied out behind a Jumbo so obviously, these leviathons can land there with the 4 degree slope. Can the 777 not land there? I could have sworn I have seen one there, but I am prepared to be corrected.

The 4 degree slope on 31R is obviously necessary because of the large rock on the approach. It generally works well as long as you configure early and fly a nice stabilised approach. It is more difficult if flying the approach to 31R with a circling to 31L (when 31R is closed) as the threshold of 31L is much nearer to the rock than the displaced threshold of 31R. Then you do have to increase the angle to achieve the correct glidepath ensuring there are no GPWS warnings.

The Fokker 100/70 I fly can cope with this approach with no problems and can in fact autoland up to the maximum of 4 degrees glideslope!

Cough
24th Apr 2008, 19:19
4 degrees to reduce noise..A 737 take on it.

For a normal 3 degree glideslope we use flap 30. For a 4 degree slope, we normally use flap 40. Pretty much the same power setting is used on the approach in the two configurations (by this I mean N1 flap30/3degree slope vs N1 flap40/4degree slope). So no reduction in engine noise for those below. I would hazard a guess that there would be a slightly greater amount of aerodynamic noise, although I know little in this area.

An enviromental perspective.

Aircraft would have gear/flaps deployed for longer. More co2.

A runway use perspective.

Due to the fact that we would have to be stabilised before descending on the glideslope, ATC would not be able to use the 160kt/4dme type speed profile. Less efficient runway operations.

Weather

Most steep approaches that I know about all have higher decision heights. Thus more possibility of a G/A (and more noise!). And no cat 3 (cue 411 comment about antique aircraft:E)

Engineering/pax comfort

Methinks that over a long time, statistically you could prove that the 4 degree slope leads to harder landings that a 3 degree slope. Yup I know its quite do able, but if you were to plot stats for MRS 31R vs others I bet the touchdowns would be slightly firmer (mistal wind excepting...)

If you want less noise at home, buy a house away from an airport! Most airports were there first (talking about my generation of folk, not old farts!)

Toodle pip!

Knold
24th Apr 2008, 19:46
As far as my understanding goes;

What makes noise on the approach is the things sticking out from the aircraft, i.e slats, flaps and gear. These will gererate vortices that create the noise.

The nice high bypass engines on newer aircraft doesn't make all that much noise. So why would anyone want to increase the GS?
Like someone wrote before me; It'll be a marginal gain only during the initial part of the glide, but it will increase the average fuel burn for an approach.

Stop building houses with one pane windows close to airports instead, or why not at all?

P.Pilcher
24th Apr 2008, 20:08
A number of years ago, I was involved in getting the Partenavia (little 5/6 seat light piston twin) approved for LCY approaches. We showed tht full landing flap had to be used for the entire approach. However the power setting needed to achieve the 5.5 degree slope with full flaps was substantially higher than that needed for the ususal intermediate flap setting used for a 3 degree one. Thus, near the airport, more noise!

P.P.

Rush2112
25th Apr 2008, 01:43
Curiously, SIA seem to be taking the opposite approach in order to cut down on wasting fuel, according to their inflight mag. They seem to be saying that they will start the descent from further away (and presumably at a more shallow angle) which somehow uses less fuel - apologies if being ignorant / dense / missing the point.

I guess coming into Changi is mostly over the sea or Malaysia anyway so noise is less of an issue. Especially coming in over Malaysia!

411A
25th Apr 2008, 02:08
They seem to be saying that they will start the descent from further away (and presumably at a more shallow angle) which somehow uses less fuel - apologies if being ignorant / dense / missing the point.


Slightly slower descent speed, and yes, it works as advertised, in nearly all jet transport aircraft.
Nothing new.
Used even in the 'ole B707, years ago, when fuel was critical and destination weather poor.

getsetgo
25th Apr 2008, 05:55
steep profiles of 4* and above can help the jet to reach runway at least( not like 777 landing short at EGLL)
but at times may cause missed TDZ,hot brakes or tyre brusts and may be overruns.
look at kathmandu approach profile where you need speed brakes to decend on proflle .
and leh aiport(elevation 10,000ft+) in Ladhakh(steep profile and commited landing as you are diving down to the r/w which is unidirectional and no go arround because mountain ahead 24000 ft high

http://en.wikipedia.org/wiki/Leh_Kushok_Bakula_Rimpochee_Airport

http://www.epinions.com/trvl-review-6692-D54393E-37A3446A-bd1

flatfour
25th Apr 2008, 16:13
I just want to thank everyone for their kind and very helpful contributions.

411A
26th Apr 2008, 20:55
does your company’s FCOM (pilot’s book) EXPLICITLY cite a ‘minimum power for approach as defined by the aircraft operating manual’ ?

No, it does not, quite simple because, unlike the straight-pipe jet engines of yesteryear...and I personally have flown many of these old aeroplanes, B707-320, JT4A powered aircraft, for example, more modern turbofan powered jet aircraft have much better engine acceleration capabilities, than in the past.

RollsRoyce RB.211 varients, especially (superb engines, no doubt about it...the best there is, in my considered opinion).

B-47 aircraft?
Gimme a break...even I am not that old.:rolleyes:

Having said this, spool 'em up by 500 feet agl, or the outcome may well not be to your liking.
By 1000 agl?
Only for those that have very restrictive standard operating procedures...read, many junior jet pilots in the RHS.

Denti
26th Apr 2008, 22:06
Well, we have the SOP to be established in a certain height above aerodrome level, established is indeed defined as having at least 40% N1 and keeping it until flare. We used to have 500ft in VMC as min height for that, sadly that got changed to 1000ft in all conditions. In the classic 737 that is not a big problem, in the NG that can be somewhat challenging, especially with tailwind and 170 to 4NM.

dscartwright
27th Apr 2008, 13:58
>Not only possible but not unknown: 4.46 deg at CMF for example.

As others have said, LCY is 5.5 degrees - and only certain aircraft are certified to do this, including the F50 and the BAe146. Actually, it's amazing how steep it can feel - I've come down the ILS there a number of times recently as SLF and blimey, you notice the difference when you're used to 3 degree approaches!

4 degrees is much more practical, though. I seem to recall that the "official" approach to RWY 04 at Norwich used to be 4 degrees because you came in over the terminal building and the cleaners were getting fed up with wiping tyre marks off the roof.

David C

B777Heavy
27th Apr 2008, 17:53
Yeah Mumbai - Chatrapati Shivaji as around 4 degrees

Mork
27th Apr 2008, 23:36
The Embraer 170 is certified for steep approaches (5.5). The 190 is on the works.

wileydog3
30th Apr 2008, 01:03
Many years ago I got to fly some proving runs on the MLS in an FAA 727 and we worked with G/S in excess of 3deg. There were a number of problems.
1) if it was winter and you had to use engine anti-ice and had to keep the engines spooked up, there was no way you were going to be near Vref for a stabilized approach even with flaps 40 which no one flies with today.. if they even fly 727s.
2) there was a lot of inertia and so you had to decide what the mins were to begin transition to the flare. 200 and 1/2 in the Tri-Motor was a real handful and lower mins were out of the question according to most of the guys who flew the profiles. So.. yes, a steeper G/S is feasible but with that comes higher mins.
3) another approach was to have a dual G/S so you descended to maybe 500ft AGL and then transitioned to a normal slope of 3.0 and this would give you time to 'stabilize' sort of...

But then, each of these approaches requires additional training and the airports required special certification. That means added $$$ to the cost of operating into that airport for the airport, local businesses that use the airport and airlines that operate into the airport. In this case, it was using MLS which was to be THE NEXT leap in technology with dual paths, circling finals, etc. Right...

EMIT
30th Apr 2008, 01:38
Bodrum in Turkey (LTFE) has (off the top of my head) a 3.9 degrees ILS for the westerly RWY. Can be flown normally with A-320 and B-757 or 767 (and other types as well, but I am not personally familiar with those). Of course one has to timely configure in order to stay on speed during the approach.
In this particular case the limiting terrain is pretty far out, about 12 miles from touchdown. ILS glidepath of course can only be set for one angle, so the whole approach is that steep. However, when in visual contact with the terrain it is possible to descend a bit below G/as so that from close-in, a (visual) slope closer to 3 degrees can be flown towards the flare.

With regards to the remark that was made in an earlier post about the very steep descent that is needed on the approach towards Kathmandu - indeed very steep, but on that section it is not possible to maintain a constant speed. In spite of flying at idle, speed will increase with maximum landing flap set. Only thanks to the fact that after that steep section there is still enough distance to go to the RWY, at a shallower descent angle, can the speed be reduced to normal values.

The steep approaches to places like London City Airport are only possible by specially modified aircraft that employ calibrated partial speedbrakes to a defined setting that is selected with a "steep descent" option selector switch (at least, that is the way the Airbus was certified for LCY).

Ace Rimmer
30th Apr 2008, 07:19
On the micro bus it works like this:

"The first point that Airbus dealt with was how to retain a stabilised speed during the approach while ensuring that the engines remained at a reasonably high power to reduce the spool up time in the event of a go-around. Using the advantages of fly by wire (FBW) Airbus has developed steep approach architecture for the Flight Control System (FCS). This feature can easily be selected by the flight crew.
The physical configuration for the steep approach architecture was defined through modelling as ‘Config full’ (flaps and slats fully extended), landing gear down, plus speedbrake panels 3 and 4 extended to 30 degrees. Extensive testing has revealed that this set up is the best lift/drag compromise.
It must be remembered that in this case speed brakes are not air brakes in the absolute sense but rather spoilers used as speed brakes, so with the extra drag comes reduced lift. To compensate for the loss of lift Airbus increased the Vref by 8kts. While this configuration and speed combination provides a desirable speed stability and flight path angle during the approach phase it proves less than ideal in the flare. The issue here was a very rapid decay in speed when power was reduced to idle, which in turn led to landings ‘firmer than the ideal’. Full retraction of the spoilers in the flare proved to be unworkable since this led to a tendency for the aircraft to balloon in the flare – a less desirable state of affairs on a short runway. This problem was solved by an automatic partial retraction of the spoilers (to 8 deg) just prior to flare initiation as the aircraft reaches a radar altitude (RA) of 85ft. On touchdown these spoilers re-extend to the lift dump position along with the other spoilers also fully deploying to their lift dump position in the normal way.
In addition, a number of other elements in the aircraft systems had to be developed to take into account the more dynamic nature of the steep approach. Naturally, the higher rates of descent at lower altitudes would cause EGPWS warnings to be triggered so the EGPWS system gain is adjusted and aural warnings have been inhibited below 130ft AGL to save pilot distraction. But less obvious are the changes to the gains in the autothrottle, AOA protection, and roll authority and flare laws".

And the procedure is:

"The system is activated once the following criteria have been satisfied; flaps/slats set to Config Full, Landing Gear down, and speed brake full. The last action is the one which in effect activates the system. So the procedure is, unsurprisingly, to set up the other parameters and as the glideslope is intercepted select ‘speed brakes full’ which deploys spoiler panels 3 and 4 as described earlier and arms the remaining spoilers for landing. Obviously, the before landing actions that you’d use in a standard approach are also performed.
The experience of hand flying this approach is very straightforward with the best technique seemingly to be to select the speed brakes to full and then pitch the aircraft so that the flight path ‘bird’ on the PFD is set slightly below the 5 deg down mark on the PFD. This would (for want of a better phrase) coarse tune the descent path which you could then ‘tweak’ to refine the rate of descent as the approach continued. Although certification testing requires that the 5.5 deg slope be maintained until flare, it’s likely that in practice that once they are visual pilots will allow the aircraft to slip a little below the ILS glideslope by changing the aim point to the runway threshold before flattening the approach slightly to a “pre-flare” if you will, just before flaring. This seems to result in a less abrupt transition, or that appeared to be the case when we tried the technique.
As the aircraft approaches the flare the automatics once again kick in with automatic call outs ‘STAND BY’ coming at 117ft AGL and 90ft AGL followed by ‘FLARE’ at 63ft. At a nominal flight path angle these call outs should come at intervals of just over a second. In the original software load the sequence was just for the call ‘FLARE’. It was determined that this could come as a bit of a surprise and result in over flaring accompanied by a balloon, so the preparation calls were added. We found that together with the slip below the glideslope technique in the last 2-300ft as mentioned above, it was effective to go back to VFR techniques and use an arbitrary aiming point on the runway which was progressively brought towards the ‘threshold’ markings with the intention of flaring as the threshold was crossed. At the same time as initiating the flare the SOP is to immediately retard the thrust levers to idle. It was discovered in early testing that the technique of leaving the auto thrust engaged until the 20ft AGL as is used in a standard approach resulted in the aircraft systems recognising a high rate of descent together with a levelling off, which caused the engines to begin to spool up fractionally before being pulled to idle. Inevitably this led to a longer float, which again is not ideal in short runway operations".


On the 170 it's more akin to the Tristar with modulation of the spoilers:

"The Steep Approach Mode (SAM) is enabled with a pushbutton switch located on the center pedestal just ahead of the speed brake handle, which is appropriate for the function. When activated, the word “Steep” appears in the Flap/Slat/Spoiler depiction in the lower left corner of the center EICAS display (the E-170 family utilizes 5 displays rather than 6). The word Steep is just above the spoilers, which are observed partially deflected in the display. Steep also appears in the upper left corner of the PFD.
To begin a steep approach, the pilot selects the Steep Approach Mode. If there are no EICAS messages, the airplane can be configured with gear down and Flaps 6 (this is the maximum landing flap setting - slats at 25 deg and flaps at 35 deg). In this configuration with SAM selected, spoiler panels 4 and 5 are positioned 16 degrees up. They will now be used as drag devices to increase rate of sink on the approach, while maintaining the normal approach speed. Embraer has successfully integrated the Steep Approach Mode so that speed additives are not required to fly the approach.

The key to success of these approaches is that the SAM allows spoiler panels 4 and 5 to move in and out in response to pilot inputs to either steepen or shallow the flight path. Since the E-170 is a Fly-By-Wire airplane, the control system senses the neutral position of the control yoke. If the pilot moves the yoke aft of neutral, the spoilers will begin to retract; if the pilot moves the yoke forward, spoiler deflection increases. These spoiler motions are transparent to the pilot in terms of control feel, but are noticed as smooth and precise changes in flight path as noted on the PFD. The gains are set such that the spoilers could be deflected from as low as 4.5 deg to as high as 23 deg. During the flare maneuver, since the pilot is moving the column aft, spoilers retract and the resulting lift capability is essentially the same as during a normal approach".