Is a 4 degree glide slope practical ?

[411A]

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]

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]

4 degree approaches

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)

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]

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]

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]

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]

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]

steep profile and current jet a/c design

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_Kus...pochee_Airport

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

[flatfour]

I just want to thank everyone for their kind and very helpful contributions.

[411A]

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.

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]

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]

>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]

Yeah Mumbai - Chatrapati Shivaji as around 4 degrees

[Mork]

The Embraer 170 is certified for steep approaches (5.5). The 190 is on the works.

[wileydog3]

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]

Some general info

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]

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".