A320/321 Speedbrake question...

[An Paddy Eile]

Silly question I know but none the less...

How much of a difference does the application of speed brake make to descent rates/descent angles??

I realise the airbus speedbrake is rubbish, and the answer depends on many many factors (weight, speed, altitude, etc.) but does anyone have any rough figures in their heads??

Just been something I've never paid much attention to...

[mourgo]

Why do you say the airbus speedbrake is rubbish?

It does a wonderful job killing speed and ROD.

[SFCC]

It is anything but rubbish. :=

[An Paddy Eile]

Sorry!

It's just my obvious ignorance!

I apologise. :(

Before starting on the Airbus, I had expected more from it. I suppose it is really in it's element at high speeds.

Sorry.

Won't happen again.

I promise. :{

So, any idea how much RoD you would expect to add by using it?? Assuming average everything? (weight, speed, altitude, etc.)

Sorry.

[Dct_Bombi]

Well discon the AP and you might get more out of it !
Curious have you just started with the green machine? PM me if you wish.

[Handfly]

The maximum angle of speedbrake defelction is different between the 320 and 321.
The 320 is capable of twice the surface defelection of the 321 but you have to have the auto-pilot out to achieve this angle.

Read FCOM 1 Flight Controls for both aircraft and you will spot the difference.

To answer your question - a good pilot can make the Airbus 'Slow Down and Go down 'at the same time (something a Boeing will not do)

Well handled you should be able to achieve 7,000 ft/min with little gain in forward speed

[toro01]

"Well handled you should be able to achieve 7,000 ft/min with little gain in forward speed"

Only with the speedbrake? No way,

only if you dive like mad

[An Paddy Eile]

Oh dear! :p

Right, how about if I ask it this way...

Let's say we're in OP DES at 250Kts (ATC restriction) and achieveing an average rate of descent of about 1,200 to 1,300 FPM. If I extend half speedbrakes (A320 with AP engaged), what would you expect the descent rate to increase to?

Dct_Bombi,

I wish I was! I'm over the sea with a G reg crowd. Are you a recent addition to EILand?

[mcdhu]

Try Expedite Descent and you will achieve 7000fpm without speedbrake as it goes for M.8/340KIAS. It's much better on the new aircraft.

Cheers
mcdhu

[Bearcat]

different weights/ different aircraft/ =different profiles

extend speed brakes out at 390 in open descent you'll get 6000fpm until your past 320.....applies to a320/ 321.

Careful in a 321 heavy, low level speed back at 220kts.....apply full speed brakes and your vls will shoot up past 235kts...

[An Paddy Eile]

I suppose what I'm after is the more static speed case really. I realise that if you are able to allow the speed to increase, and particularly if you use speedbrake also, then extremely high rates of descent are possible. But, they are reasonably short lived. (I accept that from FL390 a rapid descent can be maintained for quite a while until MMO becomes VMO)

So what about after you've reached 340 Knots with the speedbrake out? What would you expect the descent rate to settle at in that case and more improtantly, how much different from 340 Knots without speedbrake would it be??

I'm trying to get some idea of how many track miles would be too few if you're suddenly given a short cut for an approach for example. The aircraft at an average rate, descends at 250 Knots fairly close to a 3 degree path. How much does that increase with speedbrake? If you're descending at 250 Knots a steady 1,400 FPM and then with speedbrake you get 2,000 FPM then super! You've just taken one third off your required track miles. You've gone from 3 degrees to 4 1/2. From FL100, where you needed say 35 miles originally, now you only need 25.

That's kinda what I'm looking for. For average conditions, will the speedbrake add half your original RoD? A third? A quarter? Double it??

Hmmmm......... :confused:

[Mach trim]

If you really need to descend with the autopilot on try putting the gear down
with spoilers.

[TheGorrilla]

Handfly,

Which Boeings have you flown that will not go down and slow down?

[Dream Land]

I'm trying to get some idea of how many track miles would be too few if you're suddenly given a short cut for an approach for example It's called experience I'm afraid, just take into consideration that you have anywhere from ? to 230 passengers and crew on board, twisting up 340 KTS and throwing out speed brake takes it's toll on both, you will learn that the weight of the aircraft is the biggest factor when answering your question.

[WindSheer]

I believed the 75 & 76's were notorious 'non go downers & slow downers' . . . . . .:confused:

[Wingswinger]

Not at flap 20 with the gear down they weren't!

How much extra vertical speed you get from the SPBK depends on what your
IAS is. The drag varies as the square of the speed (form drag = 1/2V2SCd). The resultant increase in VS is too difficult to quantify unless you were flying the aircraft under pure flight-test conditions, flying a constant IAS and you can eliminate variables such as descending through shear layers.

Generally the effectiveness of the SPBK falls off dramatically as you slow down below 250kts Once below 200 kts, Flap 2 (add gear if you really want to descend) is the best configuration.

I'm trying to get some idea of how many track miles would be too few if you're suddenly given a short cut for an approach for example.

Try this:

Altitude x 3 = miles required.
Add 6 miles for deceleration to GRN DOT.
Add or subtract 1 mile per 10 kts tail/headwind.
Add or subtract 1 mile per 10 kts IAS above/below 290kts IAS.
Subtract an allowance for field altitude if it is significant.

EG: Descending into MAD, 290 kts IAS, 50kts tailwind, passing 13000ft QNH.

13 x 3 = 39 miles
50kts tailwind = 5 miles. Total 44 miles.
Deceleration + 6 Miles. Total 50 miles.
Field elevation 2000 ft amsl - 7 miles. Total 43 miles.

So, 43 miles is the required distance to touchdown. You can do a quick mental recalculation at any point.

You're now at 210kts/GRN DOT and given close-in down-wind vector.

sequence the Flt Pln to give you CF as the "TO WPT" ( extend the centreline)so your minimum required track miles is shown bottom right on the MCDU.

Let's say it shows 18 and you are passing 9000ft (still at MAD, 2000ft amsl).
FMGC distance makes no allowance for the turn so add 3 miles for the base turn/intercept onto the LOC. You have 21 miles to go.

You're at 9000ft (field 2000ft) so you're 7000ft above TDZ. At 21 miles. Perfect.

Suppose you were at 10000ft. You'd need 24 miles. Let's say for the sake of argument that your G/S downwind is 240 kts (fairly typical) so your datum VS to give a 3 degree descent path is 1200fpm (G/S x 5 or half first two digits).

Make sure you have Flap 1 and extend the SPDBK (if you are in a 320, you could disconnect the A/P to give full SPDBK). Check resultant V/S. Is it 1500fpm or more? (increase of 300fpm will lose you 1000ft in approximately 12 miles) so you should be on the glideslope at 9 miles albeit at 210kts so you'll need to drop the gear early (I suggest 2500ft above TDZ) to reduce the speed.

If you see that it is not losing your excess height quickly enough, gear down, flap 2 and 180kts will allow you to descend at up to 2000fpm without the speed increasing.

[Gary Lager]

If you're at the point of wondering whether your track miles are 'too few' even considering full use of speed brake then you may need to give more consideration as to whether you are likely to be able to achieve a stable approach at all.

Remember that, effectively, RoD is a 'True' Air speed, in ft/min. RoDs are higher for the same config at altitude (i.e. when the angle of descent is the same) since the aircraft has a higher TAS.

Personally, as well as the 3 x altitude rule of thumb as above for normal circumstances, anything less than that will require speedbrake, any more than about 2.5 x altitude will need prompt full speedbrake and anything near 2 x altitude needs full speedbrake, maximum flaps and gear extension (very high chance of a rushed/unstable approach and definitely better to ask for /fly extra track miles).

Of course, it all depends where you are in relation to the field - 40nm out at 20000 may give you time to make use of an increased rate of descent, 3000 at 6nm: forget it!

[Mach trim]

Let us put a different twist to the original question for a moment

If you really had to land quickly with a bad electrical fire/smoke, getting from bad to worse

Stabilized at 300 ft.60 tons (320).no wind.isa.A-320.
You are as 10,000 ft 250 knots

What would be your minimum track miles.

For the experts out there.

Autopilot off
Full spoilers.
Gear down.
Start configuring without exceeding flap speeds.
Get configured.

You would come down like a rock.

Gear down -flaps 3.spoilers out

your ROD would be ?

As someone said " exerience"

You have to calculate with what you have under given conditions and the situation. For me this is how important " situational awareness " is.
Continually updating and getting an updated mental representation of the four dimensions,

Situational awareness is key when using spoilers and always keep calculating your profile and updating.

[Caudillo]

Guys, humour me - Can't you set a target vs, leaving you in no doubt as to your present and future position on the profile, and control the speed with thrust and if necessary spoilers? Open descent is a speed lock at idle in essence right? So if you're going to control your descent rate with changes in that locked speed or by the addition of drag you've got a delay before that rate of descent achieves and stabilises, and also the original problem asked earlier - what will the rod actually be? Seems like a bit of a potluck way of doing it to me. I've understand there is more to it than I'm appreciating right now, somebody care to enlighten me?

[An Paddy Eile]

Caudillo,

It ain't that simple unfortunately!! In general, depending on weight, etc, setting a VS that results in a profile of much more than 3 degrees will result in an increasing airspeed, even with spoilers. The only real exception to this is if you have already got plenty of drag devices out such as flaps and/or gear. In this case setting a high VS and using spoilers can be very useful indeed. Intercepting the GS from above after porr vectoring would be a typical example.

Open descent is useful because it prevents any speed excursions during the descent. With a high VS, if you are not paying attention, you can quickly exceed flap or ATC speeds. As I remember it, if you are say, attempting to intercept the GS from above and the target altitude is above the current aircraft altitude, exceeding VFE whilst using VS will result in a mode reversion to OPEN CLIMB!! Very embarrassing when you start to climb at full power!!

As a new twist to the original question, what is the generally accepted best method of recovering the profile? Let's say you are at 250 knots and suddenly given a shortcut. Should you stay at 250 knots with the speedbrake until you level off, then reduce speed and confirgure, or reduce speed first, configure, then descend as quick as you can??

[Wingswinger]

Let's say you are at 250 knots and suddenly given a shortcut. Should you stay at 250 knots with the speedbrake until you level off, then reduce speed and confirgure, or reduce speed first, configure, then descend as quick as you can??

Go down then slow down. Keep your speed at 250kts, SPDBK out. Level off then reduce speed. The air is thicker low down therefore total drag is higher and the TAS is closer to the IAS thus the distance required to decelerate will be less.

[PhoenixRising]

As a new twist to the original question, what is the generally accepted best method of recovering the profile? Let's say you are at 250 knots and suddenly given a shortcut. Should you stay at 250 knots with the speedbrake until you level off, then reduce speed and confirgure, or reduce speed first, configure, then descend as quick as you can??

With the speedbrake out, get the speed back immediately to 180kts and CONF 2. Using speedbrake and/or gear in open descent you'll have no problem getting back on the profile. Your speed is also low enough to carry on configuring to get stabilised, rather than finding yourself at 250tks, clean, at 7 miles..

[Wingswinger]

The trouble is you are not going to get to below 200 kts quickly to allow you to select flap 2. You could disconnect the A/P and level-off to reduce speed rather than accept the soft elevator response of the A/P and the 5-700 fpm descent rate you would have while the speed reduces. In the meantime, more track miles are being consumed than need to be. Go down first.

[PhoenixRising]

I disagree. It's very easy to find yourself getting into an unstabilised approach doing what you you suggest. I'm talking about the intermediate approach, say 20 track miles and you find that you are high due to an unexpected ATC shortcut. Have used both methods to get down many times and the one that always works best is slow down, get plenty of drag out, then go down. You can easily achieve 2000fpm or more with 180kts and CONF 2 and use of gear or speedbrake, with the added advantage of the lower groundspeed. Also no problem with configuring further to meet the 1000' window stabilised, fully configured and on speed which most airlines require these days.

[A4]

Agreed Phonix.

A4

[F4F]

Phoenix, agree as well.
best is slow down, get plenty of drag out, then go down
Lower speed with same ROD = higher gradient :ok:

[Wingswinger]

I think we may be disagreeing about slightly different scenarios. My mental picture was of being roughly in a downwind or long base position at about 30 miles from touchdown (i.e. roughly 10,000ft) when you are given a short cut (which, by the way, you don't have to accept). In which case I would stand by what I have posted. I've been doing it (and teaching it as a "fix") for years. It works.

The TAS(approx) for 250kts IAS at various heights is as follows:
15000ft - 312kts
10000ft - 290 kts
5000ft - 272kts
3000ft - 260kts

Do you think you will cover fewer miles in a deceleration starting from 312kts or starting from 260kts? At 3000ft the air is denser hence there will be more total drag so the rate of deceleration will be greater. In addition, if the deceleration segment is level, there is no sacrifice of kinetic energy loss against potential energy loss so, again, the deceleration will be more rapid. If that doesn't completely solve the problem, you are into flap 2, gear down, 180kts and V/S -2000 to capture the glideslope from above by 1500ft or you won't stable at 500ft.

If you are thinking of a senario much closer and lower than 30 miles/10000ft/250kts, for example, 15 miles/5000ft/250kts then I would say don't accept the short cut.

[Caudillo]

An Paddy Eile
Thanks for your reply - very interesting point you make about the exceedence in VS becoming Open Climb, I hadn't been aware of that at all. I'll go away and read up on that one. There's still a lot about the airbus that's news to me in fact!

However, regarding the descent - I'm not so sure. Do excuse my unfamiliarity with the type, however I'm sure that I'm correct when saying given a height and a speed and an availability of drag, you will only ever be able to get down to another height and speed in a certain minimum period of time or a certain minimum amount of track miles covered.

I've just read back on that, and it's about as clear as mud so - if as you say, I try to vs down in a little more than a 3 degree slope, my airspeed x will increase to airspeed x + some. Fine. So if I'm unwilling to accept the airspeed increase I can go down in open climb at the original speed x, but I won't achieve the rate I wanted. All things being equal of course. I can increase my rate in this last case by spoiler, gear, holding my hand out of the window. Naturally, I'd also get an equivalent tempering of the speed increase in my vs descent if I do those.

It was the same on my last type, also a jet, and it's the same on pretty much anything I can think of. Ultimately an aircraft is subject to the same aerodynamic laws, whether its an airbus or a starling.

Of course I appreaciate what you say about the protection from overspeed offered by the open des mode, but descent in vs is hardly anything close to the bone as long as you're reasonably alert and vigilant, which I am sure we all are in any case..!
Cheers

[el #]

A very informative thread. Easy to assimilate because the plain language and practical "approach" to the matter :)
As an aviation enthusiast I understand much better now "how do you guys do it".

Thanks!

[VMK]

Fuel Metering Valve. What is it?

and.... why i read in FCOM3 3.02.07

ENG 1 (2) FUEL CTL FAULT

the procedures only apply for ground. Will it not happen on air???


why only GND.....?

[Dream Land]

exceedence in VS becoming Open Climb Knowing a few of these will be useful in the bus. :}

[An Paddy Eile]

I must agree that all the posts here are sensible and logical. (with the exception of course of VMK's post :confused: :confused: :confused: :confused: :confused: ) I agree that you can either descend, slow down and configure in a certain number of track miles or you can't, and you shouldn't throw yourself into a situation where you're not entirely sure whether it will work or not and ultimately throw it all away at 5 miles when you're still struggling to get it below 200 knots, but....

I've been trying to think about a better way of explaining what I'm looking for...

Let's say you're at 250 knots (ATC speed restriction) passing 10,000 feet or so, on a heading of North. ATC have you on what is effectively a long left base leg for RWY 27. Your estimated track miles, based on maintaining the current heading until you get a final vector for the approach at about 15 miles out, leaves you with about 35 miles to run. Just lovely!

But there is the possibility that you could turned in earlier for a shorter final of say 7 or 8 miles...

If they turn you now, your track miles would reduce to say 27 or 28 miles. Still no problem with speedbrake!!


But if they turned me later would I still be OK?? Do I need to use speedbrake now to cover both possibilities? If I knew how much extra RoD or increase in descent angle I should get, I could work that out. If I will only get a few hundred feet per minute extra with speedbrake, then I should really use it now, because it will have a longer period of time to adjust my profile. But, if I could effectively double my descent gradient, then I can wait and see what they give me as I'll still be able to manage the situation later.

Now, I realise of course that I can pay attention to what happens when using speedbrake over the next few weeks/months and I will have my answer. But, with PPRuNe available to tap into the knowledge of so many, I just can't resist!!!

So, does that make it a little clearer?? Does anyone know, or has anyone ever thought about the effectiveness of speedbrake this way before?? Am I alone in planet ODD?? :{

Hope that helps!!

Thanks everyone!

[Wingswinger]

The important thing is to keep the F-plan sequenced so that it is giving you accurate distance-to-go. That is useful information.

If you think you need SPDBK, you need it. I don't bother with trying to calculate the required VS in such circumstances. Just use the SPDBK until current altitude + 1000ft (to allow for deceleration from 250kts) x 3 = track miles to go. If it's not working, get speed below 250 and drop the gear. Don't worry about finesse, fix it quickly. I use a "gate": On glide at GRN DOT with gear down by 2000ft above TDZ, decelerating and configuring. If there's a tailwind and EAI is on, make that 2500ft. If I don't make this gate I'm probably going around.

It's better not to accept the short cut and tell them how many miles you want.

HTH,

WS

[An Paddy Eile]

Thanks Wings!

That's quite helpful actually! I've always checked my profile by working the remaining track miles and figuring out what height I need to be at. never thought about doing it the other way around!!

Thanks!

APE