A320...Autoland Distance With Autobrake Vs Manual Landing Distance With Autobrake

[kuwait340]

another question freinds,...

have a look please at QRH 4.04 (Autoland landing distance with autobrake)
configuration full...look under the weight 60.000kg ...dry runway...and auto brake low...the distance is...2130m.

now go to FCOM 2.03.20 P2 (Manual landing with autobrake)
config full ....dry runway...brakes low...60.000kg...the distance is 1710m.

the question is...why is the difference between the two distance?

why the autoland use and consume more distance ?

even if you add 8% on the manual landing distance(5kts of the A/THR) for the FCOM2 figures which is not counted (it is mentioned in FCOM2 in the bottom of the page that 5kts are not counted )...5% of the 1710m = 137m
so it will be 1710 + 137 = 1847m...still not close to the autoland distance...

i can not figure it why ?

any help please

[Port Strobe]

Not a bus driver but I'd hazard a guess at increased air distance if flare is initiated around 50' RA during autoland instead of 20' by Airbus TP?

[PantLoad]

The landing distance with autoland varies with engine manufacturer, too! The distance is slightly greater if you have IAE as opposed to CFM. :bored:

And, one more tidbit to add to the discussion...depending on the tire/wheel manufacturer, the use of autobrake during landing, in and of itself, adds about 525 feet (160 meters) to the landing distance.:uhoh:

"Why make it simple, when we can make it complicated!!!!!!":rolleyes:

Fly safe,

PantLoad

[gearpins]

Autoland ldg distance is based on Vapp whereas manual landing is based on Vls,so thats in addition to the 5 kts.It also "takes into account the dispensation on the airborne distance from threshold to touchdown" ...what ever that means.
I have it on a pp slide but am technically challenged:tried to cut and paste it. no luck

perhaps you can pm me.

[kuwait340]

Port Strobe...The FLARE mode will engage by 40ft RA(it is ONLY system engagment) but the aircraft won't flare unless it is at below 30ft RA

for those who holds A320 FCOM manuals ...reference is 1.22.30 P52a (flare mode).

any one got the answer out there ?

[kuwait340]

can anybody please explain to me why ...on QRH 4.04 CONF FULL and on FCOM 2.03.20 P2..CONF FULL...

There is NO difference between DRY or WET runway distance when using auto brake LOW ?

[loc22550]

Can anybody tell me why in QRH summary (dual hyd failure)...the landing distance calculated(wet cond) take in account the use of reverse..! although you have no reverse available...(green+ yellow)!
You can try by calculating yourself (like we use to do when there were no summary available, this calculation is now done for us in the summary table)for a certain weight, go to the table LAND dist conf full X the factor(multiply the land dist by for wet runway dual hyd failure)x factor for use of reverse, you will end up with the figure mentioned in the summary table.!
Sure i missed something somewhere ..but dont known where...!
Thanks....

[flyer146]

can anybody please explain to me why ...on QRH 4.04 CONF FULL and on FCOM 2.03.20 P2..CONF FULL...

There is NO difference between DRY or WET runway distance when using auto brake LOW ?

It's long time ago I flew the 330/340.. but I remember that the selection you make on autobrake corresponds to a certain deceleration (m/s2)-mathematical number-. This corresponds then to the same distance for the same weight on wet or dry runway. The difference will be "invisible" to the pilot (but you could feel it of course) and it is the BRAKE PRESSURE applied by the system to achieve the same deceleration that will change depending on actual factors. Of course more pressure on the brakes on a wet runway ! And of course the anti-skid system is part of this design and I would say is a MAIN PIECE to achieve the selected rate! Of course again, don't think that this would be valid on an ICY runway... but then you would use other tables, right ? (The system would still TRY to achieve the selected deceleration but could probably not achieve it on ICY runway)

What a beautiful machine, don't you think ?

Oh yeah, one more thing : once the system achieves the selected rate (mathematical number) : "DECEL" green appears on the pushbutton autobrake. On some occasions, it does not appear : the system tries to obtain it but is unable ! (exemple : contaminated runway, etc...).
Even on a wet runway, the system cannot alqys achieve it : no "DECEL" light. It depends on lot of factors on which the friction coefficient (runway type, contamination, etc ...).
So : no DECEL light is not meaning it's not working ! IT IS STILL TRYING TO ACHIEVE THE RATE BUT UNABLE TO DO ! (you might be close to the deceleration programmed or further... you don't know... your judgment !!!)

Recent accidents show the importance of understanding thoroughly those systems and always refer to PERFORMANCE charts when conditions deems it !! (ref toronto etc etc...). Never think that this very beautiful system doesn't have its limits !

See u,

Flyer146

[flyer146]

... and I forgot to mention but the use of reversers will of course be taken into account by the system : the goal being to achieve a certain deceleration (fixed nnumber); if u use reversers, you would "relieve" a bit the brake pressure. Still the same landing distance !!
This is valid of course if the "DECEL" is achieved by the system, otherwise it is still trying, not being able, and no relief of the brake pressure in this case.
I am simplifying the system, hope it's more or less clear !

Flyer146

[KIAS]

Good inputs there from flyer146 !
To add to that, if I'm not mistaken the "DECEL" light will come on as long as the aircraft is achieving 80% or more of the programmed deceleration. So you may get a "DECEL" light, but that doesn't necessarily mean you are getting the "full" programmed deceleration, but at least you're getting a good fraction of it.

[kuwait340]

Excellent Gents....

that is understood ....

but...can anybody please answer my first question...why the autoland with autobrake use more distance than manual landing with autobrake ?

Thanks

[PantLoad]

If you recall, when you do an auto-land, the thing lands farther down the runway than you usually do when you hand fly the thing. I don't know why this is (from an engineering standpoint). Also, again, using the autobrake actually increases your landing distance a bit.

PantLoad

[FullWings]

It could be explained by the possibility that for the manual landings Airbus have been using test pilot provided data, collected after much practice in ideal conditions. For the autolands, I suspect there is quite a "spread" of achieved distances, leading to a requirement for more runway.

My experience of autoland-equipped aircraft has been that the actual touchdown point varies considerably between landings, even on the latest and greatest machines. This appears to be true in the simulator, let alone anywhere else...

[sebxl]

Kuwait if you need the answer?
Call Mister BUS in toulouse via your own operation research office, they will email them and usually you can get an answer very quickly.
What I think is, it has to do with the different landing techniques, 5 kts diff, and possibly reverse use.

Seb XL

[charlies angel]

1710mx@8% vref =1847m
1847m+ 15% = @2130m
Theres an oeb ref long flare potential of the aircraft, ( up to 900m long landing!) whilst autolanding.
When planning always add 15% to landing distance to take account of a potential long landing.
Look at the oeb for various scattergraphs that the tp's achieved whilst autolanding. The 15% addition is a compromise and statistically conservative

[Robini]

I don't know exactly why but i remember when we approached ESGG/GOT
(i flew as a passenger of course :ok: ) in extremly bad sight and we did an
autoland at rwy 21.

We didn't land so far in the runway and we landed normal , after
using about 1650 m (from touching the rwy until almost stil).
And then remember that it was a 7 h flight with over 400+ passengers ,
with cargo also...
So i don't know but for an A320 it sounds pretty much to use 2130 m at
landing.

//Robini

[alf5071h]

The requirements for manual landing distance are specified in CS 25.125. The distance is normally determined with manual brakes as this in general provides the shortest distance.

The requirements for autoland landing distance are specified initially by JAR-AWO 142 - “The landing distance required must be established and scheduled in the aeroplane Flight Manual if it exceeds the distance scheduled for manual landing.”
JAR-AWO 342 (Cat 3) further requires - “If there is any feature of the system or the associated procedures which would result in an increase to the landing distance required, the appropriate increment must be established and scheduled in the aeroplane Flight Manual.”

The A320 information suggests that the autoland distance is greater than manual landing distance as a result of certification tests (JAR-AWO). Furthermore, I understand that the manufacturer can specify the use of autobrake as part of Cat 3 procedures, thus the AFM landing distance for autoland will again differ from the manual landing case.

However, note that where the difference is published as ‘advisory data’, e.g. QRH, then it is possible that manual landing distances could also have been increased for allow for the use of autobrake as the distance may not be as good as manual brake – guidelines for crew (which may or may not include safety factors – N.B Boeing data); if so, then these distances could also differ from the AFM manual landing distance.

The above points on autoland are summarized in the Airbus document “Getting to Grips with Performance” para 3.2. The increase in autoland landing distance consists of additions in both the airborne and ground roll phases; these are determined ‘statistically’, but the explanation is not very detailed (or particularly convincing).

The Boeing version of flyer146’s description of autobrake/reverse contribution to deceleration is in the presentation Stopping on Slippery Runways. (www.pilots.or.kr/upfile/aip/9AAAA_StoppingonSlipperyRwys2.ppt) A more recent version is in - Landing on Slippery Runways. (www.smartcockpit.com/pdf/flightops/flyingtechnique/0018/)
A version of the above was given at the 59TH International Air Safety Seminar 25 Oct 06 – Paris, France and is available on CD from the Flight Safety Foundation.

[kuwait340]

alf5071h

Thank you Very much...this is getting more clear for me now...

i am looking at the links you attached to put the whole picture.

thanks once again.

K340

[flyer146]

Indeed !
A lot of different numbers to talk about the same thing.
The numbers presented by Airbus in the QRH (manual ldg distances) are "test pilot" numbers (this can mean no flare, max braking etc...) : it is all a question of certification and definitions...
Let's be aware that some of those numbers just do not represent our day to day job and do not contain margins (!)
Thanks for the good question !
Fly all safe.
flyer146

[Screwballs]

I did a search about autobrake rates and couldn't find what I was looking for but this thread seems to have people who might know the answer. What are the deceleration rates for the Airbus autobrake settings?

I know the B737 technical website has it for the Boeing, is there an equally authorative website dealing with the Airbus?

Thanks for help & suggestions,

Screwballs

[charlies angel]

A320 FCOM figures
Autobrake LOW:
4 secs after gnd spoilers deployed signal; brakes demand decel of 1.7m/s2
Autobrake MED:
2 secs after gnd spoilers deployed 3m/s2
DECEL light illuminates if >80% of this rate is being achieved.
Regards.

[naceur]

deceleration by brakes starts at
medium 3 sec after touch
low 5 sec
decel comes at 80% of selected rate
(80 % may come with spoiler reverses before brakes application)

[naceur]

my mistake about the secs
i checked in fcoms
4 and 2

[JSF1]

The autoland distance calculation uses an airborne distance obtained from flight testing - determined as the mean touch down distance from runway threshold plus 3 times the standard variation on this distance.

This is added to a ground distance calculated with max braking starting at the mean touchdown speed plus 3 times the standard variation of this speed.

The combined airborne and ground distances are then multiplied by 1.15 to give the automatic landing distance.