A320/321 Speedbrake question...
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A320/321 Speedbrake question...
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...
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...
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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.
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.
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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
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
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Oh dear! 
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?
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?
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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...
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...
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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.........
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.........
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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
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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.
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.
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.
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.
Last edited by Wingswinger; 10th May 2007 at 07:34.
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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!
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!
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Electrical smoke/full spoilers
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.
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.
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thread drift here, sorry
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?
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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??
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??