Side Slip (wing down/cross control) Landing Technique on Airbus (A330)

[titaniumwings]

Dear Learned Ones,

I learned that Airbus recommends the crab/decrab at flare method while Boeing does the wing down/cross control side slip method at about 400'.

During conversion from Boeing to Airbus, I was told once by an instructor that the Airbus aircraft will crash if the cross control method of Boeing is used on the Airbus. However he did not explain or elaborate further.

Can someone please give me a technical explanation on this? Your help is very much appreciated.

Many thanks.


ps: someone also told me that the A380 may be able to do the side slip method.

[vilas]

titaniumwings
In AB FBW when you move the stick to one side it is rate roll demand so computers will position flight controls to give you that. You are trying to fly straight with wing down so the computers will try to correct that by use of spoilers, aileron and rudder. It may lead to over use of rudder which can have serious consequences. When you are try to do something that is against the design concept the result cannot be predicted.

[ACMS]

That's funny because I've landed the 330 with wing down into wind just like a 777 and it doesn't get confused or crash....:D

Indeed it's supposed to behave just like a real Aircraft.

[ACMS]

A330 FCTM---


LATERAL AND DIRECTIONAL CONTROL FINAL APPROACH In crosswind conditions, a crabbed-approach wings-level should be flown with the aircraft (cockpit) positioned on the extended runway centerline until the flare. FLARE The objectives of the lateral and directional control of the aircraft during the flare are: • To land on the centerline, and • to minimize the lateral loads on the main landing gear. The recommended de-crab technique is to use all of the following: • The rudder to align the aircraft with the runway heading during the flare. • The roll control, if needed, to maintain the aircraft on the runway centerline. Any tendency to drift downwind should be counteracted by an appropriate lateral (roll) input on the sidestick. In the case of strong crosswind, in the de-crab phase, the PF should be prepared to add small bank angle into the wind in order to maintain the aircraft on the runway centerline. The aircraft may be landed with a partial de-crab (residual crab angle up to about 5 °) to prevent excessive bank. This technique prevents wingtip (or engine nacelle) strike caused by an excessive bank angle. As a consequence, this may result in touching down with some bank angle into the wind (hence with the upwind landing gear first).

[ACMS]

So.

In the Flare---

Rudder to align the nose straight down the runway.
Aileron used as required to keep it over the centerline and not drifting downwind and if the xwind is strong enough land on the upwind wheels first. Yep a small gentle sideslip.

Basically like a 777.

You will find that unlike a 777 the Airbus won't require Aileron to keep the wings level while pushing in the rudder during a gentle crosswind, the FBW will do that for you. ( it's supposed to but........)

[titaniumwings]

Thanks a lot for bringing up the points. It is what I had wanted to discuss.

As villas mentioned; the FBW flight computer may introduce an input which is contrary to that of a pilot.

As ACMS mentioned, the comparison I am trying to make is between B777 to A330. Also the part of which it can be flown like any other aircraft may need more thought. But you will be a great person to compare as I believe you have flown both the B777 and A330.

Consider a conventional turn, any aircraft (other than airbus) will require the pilot to hold in the input on the aileron to continue the turn. For airbus just demand a roll rate till the bank angle and release to neutral-this is not conventional.

I believe the B777 sets itself up for sideslip at 400', this can be observed on its autoland.

The A330 has normal lateral law till practically touchdown. Considering the way it coordinates for the turn, it therefore cannot do a wing down at height (400' or higher) like the Boeing.

During flare however, momentarily wing down before the coordinated lateral inputs by the flight computer will result in the wing down touchdown. This is just my interpretation of the normal lateral law.

Please correct my understanding accordingly.

ps: by this theory, with an all engine flameout and still under Normal Law and the engines do not light up, it is not possible to the side slip/ forward slip method to lose height while still maintaining track on finals

[titaniumwings]

ACMS, can I just check where is this part about the wing will remain level even after you centre the heading with rudder is interpreted from.

It may be the same principle that I use to reason out the above.

Thank you very much.

If you are on a straight and level flight then you put in a rudder input, using the Lateral Normal Law as a guiding principle, what would the aircraft do?

[hikoushi]

I get the opportunity to make crosswind landings in the 330 with anywhere from a 10 to 30 knot direct component fairly regularly so this is my 2 pesos. These are just observations gleaned from drinking myself into an obsessed self-analytical stupor after making a few LEGENDARY "crunch-on" crosswind "arrivals". They have since gotten a bit better. Read on for some ideas; take what you can use and chuck the rest.

In normal law, roll and yaw control remains the same until the main wheel touchdown, at which point lateral control blends down to a direct stick-to-deflection relationship.

Pitch, on the other hand, changes to a direct stick-to-elevator relationship around 100 ft RA. Autotrim also stops, and at 50 feet a slight nose-down moment is applied to get you to pull through in the flare. This all combines to basically make the airplane feel like a Cessna 172 IN PITCH during the flare and touchdown, assuming the autothrust isnt jumping around too much. In roll, if you use a "kick-out in the flare" kind of technique and have a gentle touch on the stick, it also will feel fairly intuitive if you just look out the window and fly it.

Autothrust, however, can really mess up the feel of the flare on a gusty day.

In Normal Law ABOVE 100 ft, the FBW maintains 1 "G" corrected for pitch, regardless of gusts or thrust changes. That does not mean it will necessarily hold the PITCH exactly stable, but the G LOAD; subsequently the pitch stays pretty close. So let's say as you motor down short final, you hit a big old sinker and lose a few knots below Vapp (assume we are below 400 ft so GS Mini has stopped "mini-ing", and above 100 ft so we are still in fully normal Normal). The airplane will hold CLOSE to the current pitch as the FBW applies up elevator to increase "G" against the "sinker". Simultaneously (actually a little after), the A/THR will blast in some power to bring up your speed. This would conventionally cause a non-FBW airplane to pitch UP due to "pitch-power couple", but of course the FBW counters this as well. So to you the airplane's path feels fairly steady, with no input needed on your part except for small little "guiding" touches when the path wanders off as the airplane works to maintain "G".

Now we get into "flare mode", below 100 feet. Remember our PITCH CONTROL ONLY has returned to a DIRECT relationship between stick and elevator, with no autotrim. A/THR, however, is STILL in "SPEED" mode. Let's say you hit that same sinker NOW, at 80 feet. The nose will drop with the "sinker", and you will correct for it. This feels natural and lets us have an intuitive feel for the airplane's energy state just above the ground, where it matters most. However, as the power surges in the "pitch-power couple" is also back with us, and the nose wanders up and down. In a Boeing, we have our hands on the throttles and feel them moving, giving us an instinctive grasp of what the power, and therefore the pitch, will do. On Airbus aircraft that is not the case. You really don't know what the hell the thrust is doing until a split second after it "does", because you are looking out the window and the engines are too far back to hear until they really crank up. So when the autothrust starts jockeying itself in gusty winds just above the flare, a lot of "stick-and-rudder" type pilots will feel just a touch "out of the loop".

So going back to the gusty crosswind landing, if your SOPs allow it, manual thrust is much more intuitive, assuming you have practiced using it. A good technique on the A330-200 is to set the power for around 1.6 ~ 1.7 EPR while all set up and riding down final. Use small power changes (.1 or less) to counter airspeed TRENDS, and allow the exact IAS to wander slightly in the gusts, preferably on the higher side. The autothrust is rough in gusts because it AGGRESSIVELY tries to maintain the EXACT speed at low altitude; maintaining ENERGY STATE is more the name of the game hand flying. It is also MUCH smoother on the passengers' ears (and the neighbors' around the airport).

Most important this puts the pitch-power couple COMPLETELY back in your hands, taking away the variable that seems to destabilize crosswind landings more than any other IMHO.

So we have pitch dealt with. Now the lateral. Roll stays in Normal (roll-rate demand) till the ground. So same as pitch, it will NOT lock in your bank angle, but your RATE. So zero stick deflection equals zero rate. It will try to correct back to zero if it is disturbed, and that correction puts it back more or less where it started, but not always. So there will be some "guiding" to do here as well BUT NOT MUCH. That does mean that as you squeeze out the crab angle with the rudder, it will try to hold zero roll rate. It does a good job of this right up to the point that a gust nails you in the de-crab. NOW, it will zero the roll rate but not always exactly on wings level. This is where we usually start "stirring the pot" and it gets really wonky (like the Lufthansa A320 near-accident a while back). Small, steady motions are the key. Big, steady motions if those don't do it, but above all steady and not jerky. Think Cessna 152 more than Boeing 747. Remember a given lateral stick deflection commands a given roll rate; the airplane may take a moment sorting out how to give that to you, so hold the command STEADY until it either starts moving in the right direction or you are ABSOLUTELY sure that it will not. Let it do the work for you; by getting your control inputs "out of phase" with what the airplane is trying to do for you, the famous "Airbus Hula" will begin and your landing is SHOT.

The secrets of the guys I've seen who do really good crosswind landings mostly involve:

Use manual thrust. Since you are controlling thrust directly now, idle the throttles slowly like you would in a Boeing, to reduce pitching tendencies. Squeeze out the crab as late as possible DURING the flare and not before, to minimize lateral stick corrections. Small, STEADY pressures on the stick; use STEADY, CONSTANT PRESSURES in pitch below 100 ft, with small, STEADY, intermittent pressures in roll that ALWAYS RETURN TO NEUTRAL.

And even then sometime the damn thing just drops like a brick, and lands itself on the wrong wheel while everyone else in the cockpit laughs at you.

Good luck!

[Goldenrivett]

villas,
You are trying to fly straight with wing down so the computers will try to correct that by use of spoilers, aileron and rudder. When you are try to do something that is against the design concept the result cannot be predicted.
This Airbus produced document doesn't agree with you.

http://www.skybrary.aero/bookshelf/books/179.pdf

"With higher crosswind (typically above 15 kt to 20 kt crosswind component), a safe crosswind landing requires:
•
− A crabbed-approach, and
− A partial decrab prior to touchdown, using a combination of bank angle and crab angle (achieved by applying cross-controls).
On most Airbus models, this requires touching down with:
− Maximum 5 degrees of crab angle, and
− Maximum 5 degrees of bank angle."

[titaniumwings]

hikoushi,

Great writeup. :ok:
Thank you very much for sharing your experience and the enlightenment. Really appreciate it.


Regards.


ps: If you are on a straight and level flight then you put in a rudder input, using the Lateral Normal Law as a guiding principle, what would the aircraft do? TQ.

[Georgeg13]

Some really interesting lines written by Hikoushi...:)

[vilas]

Goldenrivett
If there was no problem with side slip technique then all that write up was unnecessary, then why not fly wing down cross control like any other aircraft? There is a problem as I mentioned. If you carefully read what you quoted it is applicable in your own words prior to touch down. It does not mean you fly side slip approach and there is a bit of jugglery involved. You fly the crab all the way to flare and when you align the nose down the runway if you start drifting down wind you put on max 5 degrees bank to stop that and if the crosswind is too strong you land with partial drift. I Don't know about 777 but I have flown a lot the 747 and A320 is not flown like that. And I have to disagree with hikoushi about manual thrust in gusty wind. It is exactly opposite of what Airbus recommends. You don't knock out GS Mini and convert AB FBW to Boeing it is not a safe way to fly. It is safer to change your company and fly a Boeing instead.

[vilas]

ACM, goldenrivette
Your post 3 and 4 are contradictory. In post 4 FCTM extract does not tell you to use side slip technique. You only use roll to stop the drift after flair and in that you may keep some crab and some bank in very strong crosswind. It is done prior to touch down and not in approach.

[vilas]

titaniumwings
Your post 6 is correct except all engine flame out part. I don't know what you mean by that. Any way with all engine flame out you do not remain in normal law. With both AC busses and G+Y knocked out you are in alternate law.

[titaniumwings]

vilas,

It should be in alternate law. I suppose that means that side slipping to lose height is then possible?

Thanks for checking n cheers.

[vilas]

titaniumwings
It is not that you cannot side slip the Airbus but you should not. And I see that you are obsessed with side slip for loosing height. This is very dangerous as it may cause brake up of the tail plain. Use of too much and rapid rudder input caused fatal accident of A300 in New York. It is not to be done.

[pontifex]

I trained in Canada where they taught the wing down technique. When I got back to the UK I was made to use the crab technique by RAF QFIs. I continued with the latter until I got to ETPS and subsequently onto B Sqn at A&AEE. During my time there I did a considerable amount of work on landing techniques where I was given carte blanche to try what I liked. My findings were conclusive - wing down is far superior. OK, so you land on one wheel, but you are still, in fact, still partially wing bourne at this time. Advantages are as follows: the fine judgement on when to kick off drift is very difficult to get right and, if you don't, the ac will land with crab on which can significantly stress some ac. In strong, gusty X winds, with wing down, you land with the control deflections which are exactly what you want for the roll out which prevents the arm and leg blurr that usually follows a crab touch down. It is easy to land without drift because the instant of touchdown is not critical and so is a much smoother. I have used this technique with ac ranging fom Slingsby T67s through to VC10s taking Comet and Lancaster en route. The only ac not suitable for this treatment are things like 747s A340 and B52. Incidentally, I have fair experience on both A320 and B737. There is no mystery - they both handle like normal ac. In fact I found the A320 a little nicer to handle manually than its rival. (Retire to WWll bunker at the end of my garden). As you may appreciate this is a big hobby-horse for me, but I do wish the RAF had been broad minded enough in times past to get away from sacred cows and try different techniques.

p.s. I never ground looped a Harvard and so have disproved the old saying "There are those who have ground looped a Harvard and those who havn't yet"

[pontifex]

Vilas.

The A300 accident was caused by more than simple unidirectional rudder movement. There were at least three rudder pulses, each one reinforcing the previous one. The ac didn't have a chance.

[vilas]

pontifex
I am aware of the reasons for that crash and after that Airbus has made a video presentation on use of rudder in transport aeroplanes. The point I am making is in Passenger jets you do not use manoeuvres like sever side slip to loose height.

[TyroPicard]

titanium wings
ps: If you are on a straight and level flight then you put in a rudder input, using the Lateral Normal Law as a guiding principle, what would the aircraft do? TQ.
In Normal Law side stick neutral the a/c will try to maintain zero roll rate. If you apply the rudder slowly the bank angle will not change much; if you boot the rudder the FBW cannot cope and the aircraft will roll initially then stabilise provided you maintain constant rudder deflection.

You can fly a side slip in an airbus the same way as any other aircraft... Rudder in the opposite direction to the bank angle, and fly the required attitude.

[titaniumwings]

:ugh: That's a 'good' one!!!

Another thing which I was told; Airbus does not build its landing gears to withstand the lateral loads of landing without decrabbing. Such a 'technique' usually results in significant damage.

Just to share.


vilas; i am going through hell-day contingencies being new to the bus. One of the scenario given is all eng flameout. Am thinking what to do when you are on finals and high, not high enough for an orbit but high enough to have the speed being excessive. Better be prepared with my plans and options rather than thinking about it when the sxxx hits the fan.

[titaniumwings]

TyroPicard,

Thanks for your reply. As you said because there is no input in the side stick there should be no bank. There is pitch and lateral law but there isn't any yaw law as I thought it is to supplement the roll (lateral). I think the yaw is used by the computer to coordinate the turn. Hence when there is no turn the computer will neutralize the rudder. But when the pilot makes a rudder input, will the computer try to counter this with the primary objective as 0 roll rate?

I am not trying to split hairs or be an engineer but I really hope to know and understand what the aircraft does especially maneuvers which is close to ground where I don't have much room to play or experiment with.

[vilas]

titaniumwings
If you are new to the Bus then FCOM and FCTM should be your bible. If you didn't understand something from that you can ask some one to explain in PPRUNE. Do not learn flying here. Lot of things some incorrect and some downright dangerous are suggested in these columns. The most dangerous thing to do is start making your own procedures in Airbus FBW. Airbus is flown only one way and that is airbus way. There is no place for experimentation listening to some one no matter how experienced he is. Do not compare it with previous aircraft. One very senior airbus industry instructor told me if you have taken a new girl friend do not compare her with your old one the result will not be pleasant. Also I can feel you are reading procedures as if they are horror stories. In air if you misjudged something there is limit only within which you can recover. If everything was recoverable there would be no accidents. You don't side slip big aircraft and first try to fully understand laws in normal flying and not aerobatics.

[titaniumwings]

Once again I thank you those who give me advice and recommendations especially on techniques.

I have developed an approach to my operations (but always learning and in the process of refinement). As a pilot it is important to know the books. Attention to limitations are essential. Those are usually non-negotiable. When reading the books attention to the wording is important. Most of them are written with much thoughts. 'Must' and 'should' are used appropriately.

Beyond knowing the books understanding the underlying reasons helps to mature one's operations. This is especially true for recommended techniques. There are many instances of instructors debating over different techniques but the management usually takes the macro view of pilots exercising their judgement and determining what is the best course of actions. This is to the exception where certain techniques which may be prohibited due certain restrictions. These limitations must be adhered to.

I listen to the range of views and opinions especially those with accompanying reasons. This develops my understanding and judgement in determining the best course of action. I will comb the books and web for answers and when not satisfactory I may consult as much resources as I could. After getting the range of opinions I have to evaluate critically and determine the best course of actions.

Nonetheless I appreciate any effort to share. Again, much appreciation for the spirit of sharing guys. :ok: Also I will decrab for landing :)


Ps: Airbus told me that this aircraft can be flown like any other aircraft. But I feel that it is essential to know their FBW laws and characteristics. I also read their FCB: Yaw Disturbances During Takeoff Roll which pay special attention to the improper use of rudder. An accident that I have visited was AA 587 which was a B737 nonetheless. I try to learn from all the incidents and accidents, don't think I live long enough to make all the mistakes especially the ones I learned.

[roulishollandais]

Cadet pilots are no more taught down wing technique in France and learn realistic cross-wind in airliners with passengers:{

[titaniumwings]

Thanks for the info. Just for interest sake, can I verify that it is also such for Boeing, especially B777? Cheers

[Denti]

Can't say for the big twin, but for the 737 the sideslip (wing low) method is actually one of the boeing approved methods, up to a crosswind component of 17 kts at flaps 15, 20 kts at flaps 30 and 23kts at flaps 40.

Two other techniques are described, one being touchdown in full crab, which is approved up to the 40kts crosswind limit, but not recommended on dry runways, however is recommended on wet or slippery runways. The other one is the overall recommended technique of de-crab during flare.

The fail operational autoland uses a mix of wing low (up to 7° of bank if memory serves right) and crab.

[737Jock]

decrab in flare on both 737 and a320. Have never seen a 737 come down with wing-low method on approach. If you do this you are a minority.

As for all engine out method, just stick the nose down and pitch for the runway threshold at FULL flap. You won't be at optimal glidespeed so you loose altitude faster.
Unless you picked the shortest runway in town the wheelbrakes will stop you, just don't try to achieve a smooth touchdown.

[stilton]

Usual hysteria about 'sideslip in airliners'


If it is that dangerous then why is it built in to every autoland system on modern Boeing aircraft ?


Try watching the different stages of autoland to see this wing down correction introduced by the autopilot, very smoothly while limiting the bank angle at touchdown.


In manual flight it nearly always produces a better, more predictable result than the 'push it straight at the last second' technique.

[vilas]

stilton
By slide slip I do not mean wing down approach. titaniumwings wants to slide slip to loose height. I would like to know which commercial aircraft manufacturer recommends this.

[titaniumwings]

Thanks for sharing the different techniques on different types guys.

Denti, B777 seems to share similar techniques to the B737. The gears can take the no de-crab. But most pilots would.

I was asking for recommendations. Thanks to 737Jock for his recommendation

vilas;
I would like to reiterate my position: I am trying to investigate and reaffirm my knowledge of Airbus FBW laws and characteristics. In the process I also thought about contingency plans for all eng out forced landing piloting techniques especially to losing height at finals in case of being caught high and fast. I am not about to give up in that situation and have learned of a few techniques which did include side slip to lose height in my early days. I have not seen an outright limitation on this nor am I recommending it. Neither could I find a recommended technique for this situation in FCTM. I am open to suggestions and would be enlightened if I could be pointed to the reason(s) as to why not for this technique, be it references or even technical explanation. I have in mind more than 1 technique and had evaluated the plus and minus of each but I always like to learn from others if they are kind enough to offer.
Thanks in advance to those who do. Cheers guys.

[ACMS]

Vilas----gidday again mate, in the flare during a strong crosswind you will need to apply ( with a crosswind for the right ) LEFT rudder and then RIGHT Aileron into wind and probably have to hold those inputs in to control the Aircraft smoothly onto the ground on the upwind wheels.

So isn't that a small sideslip?

Unless you are very quick and push the rudder quickly to align the nose just before touchdown and don't need any wing down you MUST have to apply opposite control input at the same time....

Sideslip.....

Anyway mate it works for me.

I assume that's what you do as well?

[ACMS]

Titaniumwings-------Also remember the Transat A330 dead stick approach after running out of fuel over the Atlantic, the machine glides so well they needed to use a lot of side slipping after getting too high on their approach. Worked well for them on the day and they managed to land and stop with blown wheels.....ok:

Not that I would sideslip in any other situation in a commercial Jet but in an Emergency like they had all bets are off!! You do what you need to..

[vilas]

ACM
You hold the crab till flare. After flare you straighten the nose with rudder or hold 5 degrees crab if too strong a wind and use stick as required to maintain direction or the centre line in that you may use 5 degrees of bank before touch down. That is the recommended technique for all not only for you. The dispute is can you do it from 100ft or 200ft? Airbus does not recommend it and the reason is stick out of neutral is rate of roll demand. If you want to do it ask the airbus. Don't develop procedures on your own or drag Boeing procedures in AB FBW.

[Gryphon]

OK, I'll review it for myself.

When talking about if you are able to land the Airbus FBW (I only know 320 family) in crosswind using the "wing down/cross control side slip method", I'd like to make different considerations.

- Airbus clearly recommends the crab technique. Why? They didn't tell us! But it is a recommendation. They didn't say it's a must or any other technique is prohibited or any other technique is not possible or discouraged because the flight controls. In the other hand if the manufacturer is recommending you something....better to follow it! But still a recommendation.
- There is nothing in the flight controls system that prevents you to do so. You make a roll input in the sidestick to produce a roll rate until you have the target bank and then go to neutral to order roll rate zero and the desired bank will be maintain (it doesn't matter if the target bank is zero or 5 or any other until 33 or if you are changing your heading or keeping it). Of course in real life you have to work on it the same way you have to do it in every landing, with the only difference that the target bank won't be zero. Simultaneously you use the rudder to align the aircraft with the runway centerline. You will flight straight and the computers will be happy because they are doing what they are supposed to do and nothing else. Just the same way you'd fly any other aircraft.
- Is it difficult? I don't think so, but as any other technique, has to be trained, and the more you do it the easier it become. Will you train it? I don't think so because it is not the recommended technique.
- ACMS and hikoushi: wise words, thank you!
- Titaniumwings: don't worry! You won't crash so easily! Just an aircraft! Enjoy it! :ok:

[titaniumwings]

ACMS: How can anyone forget Air Transat 236, an Airbus 330. You put it in perspective.

Gryphon: I have considered your approach, interpretation and technique analysis. Totally agree with you philosophy and perspective.

Wise words by wise aviators!! Thanks for the learning and sharing session. :D

[ACMS]

Vilas-----mate mate mate

Please re read my post particularly the underlined bold part where I stated with emphasis I was speaking of during the flare manoeuvre. No where did I say to start the side slip earlier, a technique I have seen on conventional aircraft but not on Airbus FBW. I don't use that technique myself either.

Eaelier I posted the A330 FCTM reference to crosswind technique which I do follow quite well even in gusty typhoons as per Airbus and company policy/training, so I'm not using my old 777 737 747 experience. ( although they are indeed the same )
Cheers

[Goldenrivett]

Villas,
The dispute is can you do it from 100ft or 200ft? Airbus does not recommend it and the reason is stick out of neutral is rate of roll demand. If you want to do it ask the airbus
How much side slip do you think you have with a badly trimmed aircraft during an engine failure on take off? Even with a big side slip, the bank can be held constant with neutral side stick. The tail doesn't fall off either.

At some time or another, most pilots will have flown the Airbus sim with lots of side slip and not realised until spotting the Beta target / slip indicator. You don't need constant aileron to control the slip induced roll. The computers are doing it for you.

What do you think the FBW computers are doing differently when side slipping at 2,000 ft with all engines at symmetrical power and flying with the slip indicator not centred during EFTO?

[vilas]

Goldenrivett
It is my well considered opinion that pilot should stick to Airbus recommendations in FBW aircraft. Because line pilot does not have access to the software, hardware or wind tunnel or has the training or opportunity to test fly. Also the manufacturer is in touch with all customers across the globe and is aware of all incidents. Therefore they are in a better position to approve or disapprove certain way of doing things. If you develop your own procedures in isolation there may not be a crash but in different circumstances and situations it may lead to undesirable state. Can you side slip an airliner to lose height like a small trainer? If your answer is yes I have nothing more to say but good luck. Till the A300 crashed in New York they didn't know that overuse of rudder can cause the tail to brake off did they?

[vilas]

ACMS
If you read what I have been saying you will realize that we are saying the same thing so where is the argument.

[Goldenrivett]

villas,
In post #35 you said Airbus does not recommend it and the reason is stick out of neutral is rate of roll demand.

All I'm asking is why you think you'd need stick out of neutral to maintain bank / wings level with side slip and why you think the rudder loads with constant side slip is enough to break it - yet it must be designed to withstand rudder loads with EFTO.
Till the A300 crashed in New York they didn't know that overuse of rudder can cause the tail to brake off did they?
You don't seem to be very confident in the loads the Airbus fin can withstand under constant rudder deflection. How will you cope with your EFTO?

Can you side slip an airliner to lose height like a small trainer?
Suggest you read The Gimli Glider ? Damn Interesting (http://www.damninteresting.com/the-gimli-glider/)
If the options are to do a forced landing beyond half way down a short runway, or loose some more energy on short finals - then I might try side slipping. In normal ops, side slipping is simply inefficient flight.

[TyroPicard]

titaniumwings
As you said because there is no input in the side stick there should be no bank
That is not what I said! Excuse me for shouting, but Airbus FBW in roll WILL NOT MAINTAIN CONSTANT BANK ANGLE. Stick free it tries to maintain zero roll rate, but if the bank angle is changed by turbulence or rudder input it will try to stop the roll, but IT WILL NOT RETURN TO THE ORIGINAL BANK ANGLE.
Is that clear enough?

[titaniumwings]

TP- bear with me for a while. I m not trying to be funny but let me try this one more time. Say do a right turn then neutralise the side stick at 5deg right bank. Then put in left rudder input gradually gently. What will the bank angle then be?

Thanks.

[FlightDetent]

I'll try: the bank angle will be whatever the presumed rudder input will create. Large possibilities available with swept wing.

No lateral SS input, no roll demand. Unless, of course, you can take her beyond 33 degs.

[ACMS]

Vilas----ok good after you re read my post above:ok:

Gentle controlled smooth sideslips ( partial rudder applied ) at low speeds are not going to knock the tail off, the AA A300 in JFK was sudden full rudder control that placed rapid excessive sudden loads on the fin.

Anyway blue skies...

[hikoushi]

"And I have to disagree with hikoushi about manual thrust in gusty wind. It is exactly opposite of what Airbus recommends. You don't knock out GS Mini and convert AB FBW to Boeing it is not a safe way to fly. It is safer to change your company and fly a Boeing instead."

vilas, methinks you are trying to say that either the Airbus or the Boeing aircraft line is safer than the other, but I can't quite tell which one. Either way, horse-pucky.

I see according to your profile that you are a sim instructor on the 320, but have not flown the 330. In the training world it is easy to lose touch with real flying, yes? Remember the Airbus Golden Rule that it "...can be flown like any other aircraft"? The rule at the very front of "The Book"? Yes A/THR is the way to go most of the time; the FBW is designed to work with it and it all does a very good job. However, the 330 has very smooth and responsive throttles and is a joy to truly hand-fly as well.

GS mini is done doing it's "thing" as you descend through 400 feet. It does a great job of keeping an energy reserve and preventing excessive thrust changes. Below 400 feet, the GS mini function blends out. Your target speed becomes your Vapp, and with shear and gusts (big ones) it is common to have that speed drop to Vls and a great big burst of power come in, suddenly and without warning, slightly out-of-phase from the wind. Think back to your 747 days and all the inertia of a big heavy airplane, then couple it with the Airbus FBW and autothrust. This is where a steady manual thrust setting can be more comfortable IF you are comfortable, proficient, and current at actually using it. Barring the wild winds we are talking about here, the A/THR GENERALLY stays ahead of the speed very well AS LONG AS you have good pitch control (and incidentally if you have trouble keeping the nose pointing straight on a single-engine ILS in the simulator using autothrust, I guarantee you your pitch control is junk).

Do you fly the 330? If so, do you fly frequently enough into gusty winds to have become comfortable with them IN THE 330? Do you fly, and have you used, manual thrust enough to be as comfortable with it as with the autos? If not, does your company allow the A/THR to be deferred or MEL'd? Ours does. If yours does too, and your SOP allows it, I HIGHLY recommend you learn how to fly the airplane "like any other aircraft". You state that (paraphrasing) turning the autothrust off is "not a safe way to fly"; I sincerely hope you do not wind up getting an aircraft with the autothrust deferred and having to figure it out for the first time under pressure. Practice and be comfortable flying your aircraft at ALL levels of automation, as there are times where you will NEED all of them. And if your SOP allows it (ours does), there are times where you may WANT to have a little bit bigger of a bag of tricks to choose from that are all equally comfortable and safe, no matter what aircraft you fly.

Tailwinds to you and good luck out there.

[stilton]

'Below 400 feet, the GS mini function blends out. Your target speed becomes your Vapp, and with shear and gusts (big ones) it is common to have that speed drop to Vls and a great big burst of power come in, suddenly and without warning, slightly out-of-phase from the wind'



No thanks, i'll stick with manual thrust on my Boeing :eek:

[vilas]

Hikoushi
I was not talking about individual flying ability or developing the skill to fly without auto thrust. You must acquire all the skills that it takes. I didn't fly 330 but I did A320. But starting from B707 to non FBW airbuses and classic 747, without the luxury of PFD and trend arrow I have enough in the kitty to handle well anything that others can do. I found A320 the easiest aeroplane to handle with or without any automation whatsoever. We didn't use GS mini in 747 but speed addition which was bled off at flare but GS mini is a good concept. Can pitch control be easier than airbus normal law? In a GA with TOGA power you need to pull up otherwise it gets damped. So in approach and landing a burst of power is not a big deal. You just point the bus like a gun at the threshold let the thrust do what it will. If you have good scan you will have good control.

[vilas]

stilton
If you were to fly an Airbus you will be amazed how easy it is compared to 737. That is the problem with AB FBW it takes some of the glamour away because even a well trained inexperienced co-pilot flies it equally well.

[pontifex]

Vilas

I agree 110%. I have flown both AB and B (and McDD, DH, Lockheed and Fokker). The A320 was without doubt the sweetest to handle. Equalled only by Vickers.

[hikoushi]

As much as people (who have never flown one) slam the Airbus philosophy, I must admit I have really learned to enjoy it, even with all it's quirks. It will never have the visceral feel of an older Boeing or Douglas (or Piper for that matter), but it is definitely a pleasure to fly. I still encounter Airbus pilots in all seats who never developed comfort flying the airplane and leave the autos on absolutely all the time. All of them wish they were flying a 777 instead. If they would just take the time to fly the airplane for what it IS, they would find the Zen in the Art of Bus Driving (or just bid back over to the Boeing fleet).

But you know what happens when you go back and fly long-haul in a Boeing after being on the Bus for a few years? YOU CAN'T STAND IT. IT IS PHYSICALLY UNBEARABLE to have that damned control column jamming your legs again. You never noticed it before, but after experiencing that legroom, you now start thinking about deep-vein thrombosis. You leave the autopilot on all the time anyway so you don't care that the airplane "feels" better, you just care about that damn column. And the table! Where is my meal tray going to go? And my coffee? Come on, my break doesn't start until 0900 and it's only 0300! We have a 14 hour block to ZBAA today, this thing is uncomfortable as all getout! Give me back my French ergonomics!!

Time to call it a day and go have a beer. What whining little snots we become with a little comfort!

[RetiredBA/BY]

Quote: I trained in Canada where they taught the wing down technique. When I got back to the UK I was made to use the crab technique by RAF QFIs. I continued with the latter until I got to ETPS and subsequently onto B Sqn at A&AEE. During my time there I did a considerable amount of work on landing techniques where I was given carte blanche to try what I liked. My findings were conclusive - wing down is far superior. OK, so you land on one wheel, but you are still, in fact, still partially wing bourne at this time. Advantages are as follows: the fine judgement on when to kick off drift is very difficult to get right and, if you don't, the ac will land with crab on which can significantly stress some ac. In strong, gusty X winds, with wing down, you land with the control deflections which are exactly what you want for the roll out which prevents the arm and leg blurr that usually follows a crab touch down. It is easy to land without drift because the instant of touchdown is not critical and so is a much smoother. I have used this technique with ac ranging fom Slingsby T67s through to VC10s taking Comet and Lancaster en route. The only ac not suitable for this treatment are things like 747s A340 and B52. Incidentally, I have fair experience on both A320 and B737. There is no mystery - they both handle like normal ac. In fact I found the A320 a little nicer to handle manually than its rival. (Retire to WWll bunker at the end of my garden). As you may appreciate this is a big hobby-horse for me, but I do wish the RAF had been broad minded enough in times past to get away from sacred cows and try different techniques. Unquote.



As an ex RAF standards QFI, and later Boeing TC (with time on the VC10 too) I can assure you the RAF teaches the crab technique because it works so very well on all types (although I have no Airbus experience) and on podded aircraft minimises the chance of pod strike. Why change a perfectly good technique and on my Boeing conversion at Seattle, it was a fully approved technique. The thought of significant bank near the runway with a CF6 hanging under the wing fills me with dread, as does the thought of landing in a 40 k crosswind without decrabbing !

In my almost 40 years of flying, RAF and civil, the ONLY time I ever saw a wingdown crosswind approach was when my Boeing was making a coupled approach.

If it ain't broke why fix it ?

[pontifex]

Hi there Retired BA/BY. I was also a standards QFI and also a commercial FI so our background is rather similar. I still maintain that, where physically feasible, the wing down is superior. I have also done instrumented trials on Xwind handling and the results were rather conclusive. The aircraft involved were Nimrod, C130 and PC9. In all cases the wing down was established by at least 100ft so the approach was stabilised in good time before touchdown.

[hikoushi]

Many years of wing-down landings in Cessnas and such. Flew GA from a young age and only went for the commercial path when it dawned on me that it is better to fly on someone else's dime. :)

When pursuing my instructor's certificate many moons later, a wise old eagle taught me the technique I've used since on pretty much everything. Fly the airplane in the crab INTO THE FLARE, round out and hold it just above the deck. Squeeze in the rudder to straighten the nose while simultaneously squeezing in opposite aileron to keep wings level; at the moment the nose is dead strait, keep the wing coming down slightly and continue to rudder the nose down the runway. This is, of course, EXACTLY the same technique you would use to establish your "wing-down sideslip" at 100 feet or wherever.

BUT, since you are right over the runway, your slip is interrupted by the upwind wheel pressing into the ground. It will do so with just the scarcest bit of bank, since you are "pirouetting" in the flare. Also lets you choose the moment the wheel touches, in a similar way to a wheel landing in a taildragger. And, if you blow it and flare high, you just wind up in a normal wing-down approach. In a big plane usually not even that happens, as your inertia will keep you tracking straight a good bit longer than in a lightplane (mega-winds notwithstanding).

In the Airbus I do what basically feels just like that method. Starting it right around the first "retard" call along with the final throttle reduction seems like a decent starting target, then adjust that for energy state, wind, steeper approach slope, etc.

This is of course, just a technique so take it or leave it.

So far so good, except for the first few mega-pancakes and the occasional random wonky approach (usually after a long red-eye that lands before sunrise. Good morning EARTH! "No, Tower, we don't need the trucks! I was just using the main landing gear to drill for oil here on the numbers of 23 Left! What's that? No, we didn't strike crude, that is just my number 2 tire vaporizing").

[glendalegoon]

hikoushi


a lovely way of saying it. most planes will do just fine with the crab and decrab very close to the runway, over the runway, at very , very low altitude (way under 50')

I understand why so many like the wing down method. It means they are lacking in skill, technique, and the courage to take the plane down close to the ground and do many things at once.

kick rudder

lower wing

bring nose up

and all this done at the same time or nearly so. sort of hard like walking and chewing gum at the same time.

And while we are at it, you can even use assymetrical thrust to help you along. Many will doubt this, but it is usually a lack of skill which could be developed if you like. Try it in the sim on a non jeopardy ride.

There are pilots that get by and then there are pilots that are fully in command of an aircraft.

choose the type of pilot YOU want to be.

[bubbers44]

One night I was on my first captain flight with an FO on his first Lear flight landing in a 30 knot direct crosswind. He asked how does this thing land in a crosswind? I said "I don't know, never have."

I used Glendalegoon's method including leaving the upwind engine power up some and got a great landing. It is all done at once late in the flare and is not difficult in any airplane.

[ACMS]

So did the paying punters down the back know how incompetent you were?

Surely you were "trained" in an approved FFS or if that wasn't available an Aircraft? And had completed crosswind landings with an instructor Pilot along BEFORE being cut lose in a fast swept wing Jet??????!

I don't know anyone that would suggest using differential thrust ( especially in a centerline thrust type A/C like a Lear Jet where it would be basically useless ) to get the Aircraft straight in the Flare.

THAT'S WHAT THE RUDDER IS FOR, and if it's not effective enough I would suggest the crosswind is a little excessive:D

[Capn Bloggs]

I don't know anyone that would suggest using differential thrust ( especially in a centerline thrust type A/C like a Lear Jet where it would be basically useless )
Arr ,yes, the old "engines are on the body, no assy thrust there" furphy. Ever flown a Lear, ACMS?

[vilas]

I have never understood the need to develop non standard procedures. Using differential thrust for crosswind landing is absolutely non standard procedure. No manufacturer needed it for certification nor has recommended it. On AB FBW if you forget to bring that thrust levers to idle the ground spoilers will not deploy so no auto brakes. Landing on short slippery runway not a smart thing to do.

[pontifex]

Glendalegoon

There is no doubt that the "kick off drift" technique requires more skill to produce an acceptable landing. This, of course, means that its success rate is inevitably less than wing down. As a result the aircraft is more stressed and the pax less happy. You seem to imply that, because you are an above average pilot, you would deny lesser mortals the opportunity to produce consistent, acceptable results. "Standing up in a hammock" springs to mind.

[ACMS]

Bloggsy-----nope not a toy plane like the Lear, wouldn't mind though.:ok:

Surely the differential thrust would be f all?

Anyway why would you want to do it anyway, surely the rudder is sufficient.....

Do you do it in the 717? Is it an approved method?

[stilton]

Boeing doesnt seem to have an issue programming wing down for the autoland.


As long as its not excessive there's nothing wrong with it, it produces a far more stable, predictable result.

Of course if you don't have the 'courage' to kick it out at the last minute :eek:

[scotbill]

Once again the crusty old ex-RAF types who have acquired the necessary skills for a last-moment juggling exercise with rudder and stick pour scorn on the inadequates who use easier methods.

My confidence in Xwinds was almost completely destroyed by the RAF technique in Chipmunks. Later in Scotland I was taught that the crossed controls method was the professional way to make smooth controlled landings in Hebridean gales at minimum discomfort for passengers.

Later I was able to satisfy myself that the technique works superbly on machines as diverse as the Chipmunk, Tiger Moth, Viscount, B767 - and have no doubt Airbus as well although I have not had the pleasure.
As an ex-TRE I treasure a note from a very experienced ex-RAF pilot thanking me for having undone his service brainwashing after he had carried out a max Xwind landing on the 757.

There is no question in my mind but that the controlled slip (not wing-down!) is by far the easiest method to teach and is likely to have the most successful outcome.

The B767 autopilot gives a particularly polished demonstration.

[Capn Bloggs]

There is no question in my mind but that the controlled slip (not wing-down!)
This'll be good. Please explain the wings-level controlled slip.

[vilas]

What is so difficult about removing the crab I fail to understand. The only problem I see is doing it too early causing a downwind drift. Then you use the bank anyway. You are permitted to land with 5 degrees of crab. Suppose you were late in removing the crab on touchdown the aircraft will straighten itself because of CG but if you were coming with wing down it may be more than 5 degrees and during flare you may risk engine contact. In airbus you are not dealing with flight controls directly but asking computers to give rate of roll so it positions ailerons, spoilers and rudder accordingly even if you neutralise the stick, yaw damper is positioning the rudder as long as wing is down and you need to fly against that. May be that is not desired so is not recommended.

[Goldenrivett]

villas,
yaw damper is positioning the rudder as long as wing is down and you need to fly against that.
Exactly the same in a Boeing.
May be that is not desired so is not recommended.

The probable reason is, if you fly with big side slip angles (early in the approach) on Airbus, you won't know when you are about to run out of aileron control (full deflection) due no feed back of FBW controlled aileron position. On all Boeings (including 777) it's obvious by the amount of control wheel necessary.

[vilas]

Goldenrivett
There is a little difference with non FBW. In that Yaw damper action may be same but the aileron and spoilers you directly control. In airbus the computer is in opposition to your action. So there is conflict. May be what you say also is possible. That is the reason I recommend SOP. You want to do something else refer to Airbus industry. I have done it on many issues and got clarifications from them. Doing something different without all the answers I am not comfortable with.

[glendalegoon]

ACMS...

Do you realize that many people learned to fly in the actual airplane and not in a sim? Do you realize that many checkrides are flown and that a max crosswind is not available at the time of the checkride and you can still get a type rating?

AS to assymetric thrust on planes with tail mounted engines...yes, you actually have assymetric thrust and guess what, WHEN AN ENGINE QUITS you need full rudder at some times.

AS to passenger comfort, slipping an airplane can be a bit uncomfortable.

And what really gets me is that pilots today don't seem to understand that the wind at 300' afe is not the same as it is at touchdown, so you are still FUTZING with the thing .

So if you have crabbed, can see a wind sock and can "KICK IT STRAIGHT" you are actually DOING LESS WORK than the slip method.

AS to NON APPROVED procedures. IF you don't want to use assymetric thrust, don't. But if you ever do, you will find you have more options.

And all those fancy autopilots seem to have lower crosswind limits for their landing than humans do...why is that? ;-)

Go Get Em bubbers, fly with you anytime!

[ACMS]

Yes I came from a time before flight sims and we had to learn in the Aircraft as well, I clearly remember having to do crosswind landings during conversion in the Aircraft.

I still can't believe neither you or the new FO had landed in a good crosswind and they signed you off as safe IN ALL CONDITIONS? Surely you should have found suitable conditions to be trained in to a competent standard, even if that meant waiting or flying off to another Airfield to find a crosswind....

Wouldn't happen today, in my 777 command 14 years ago we had to demonstrate competence with a 38kt crosswind at Cat 1 minima and a wet runway.....if I couldn't do it safely I would not have passed....

As for the differential thrust idea, great but I've never been trained by Boeing Fokker or Airbus to use that style ( mainly as they prefer the use of Autothrust ) and I don't think it would be wise to stuff around trying......Rudder and Ailerons work just fine for me up to Max crosswind.

Yes I realise the 300' wind is most likely different to the surface wind....but thanks for the heads up.

p.s. The 777 Autoland crosswind limit 38 kts ( NON AWO ) is the same as the Pilot limit of 38kts

[bubbers44]

Back when we were flying dozens of different types of aircraft while waiting for our shot at the airlines when noone was hiring we were competent to fly so checking out in a Citation Jet or Lear was done quickly with your charter company or what ever you were doing. No ground school, no formal training, just learning the differences and taking a check ride. We all could read a manual and get in the airplane and after a couple flight were competent in that type. No training on how to land or SOP's because we were expected to fly a single, twin cessna, Beach 18, Citation any time a flight came up. The Lear I was flying that night I just started flying so never got to do a cross wind landing until then. Since I wanted to make sure I had enough rudder to compensate for the crosswind I used some upwind thrust. If you don't think fuselage mounted engines require much rudder with assymetrical thrust you are wrong. Try a V1 cut with no rudder some day.

[glendalegoon]

ACMS

Every time I got a new plane, I would read the aircraft flight manual, especially the introduction.

It always said that the book was no substitute for an experienced pilot.

Boeing didn't teach me to fly.

I was thinking about one of the airports I fly into on a regular basis. KDCA. Its approach to the south would not lend itself to the slip method of crosswind landing. I'm sure some of you know what I'm talking about .

So, don't hit the wing, or the engines, keep it in the center of the runway and do it any way you can.

[McNugget]

I know that you like nothing more than telling people how great aviators were, back in your day (we're going back quite some time, too). The simple fact remains that having zero training as you transition from one jet to another is foolhardy by anyones standards. That's why you'd never get away with it now. Oh, but never mind, that must be because your generation were so much more skilled, back then. That'll explain why flying was so much safer 40 years ago than it is today.

However, that's completely irrelevant.

What is relevant, is your assertion that a LR provides asymmetric thrust on approach. Ha, having flown one, and also having landed one with an engine inop, I must ask you whether you were joking? The asymmetric thrust experienced during approach power settings needs nary the slightest squeeze of rudder. To pretend that you need it as an option on approach is, frankly, laughable. To even consider it as a possible option would suggest that you're flying too many types, therefore unable to apply the basic aerodynamic principles pertinent to the one you're sat in.

We're not talking about V1 cuts with 'no rudder'. We're talking about differential thrust on a CL thrust aircraft on approach. With rudder.

Can you do a checkride on a LR to remove your CLT limitation? I didn't think so.

[glendalegoon]

mcnugget

are you saying flying a learjet means you are flying a center line thrust airplane?

tell me, what other planes with engines mounted on the fuselage are center line thrust?

[scotbill]

Quote:
Originally Posted by scotbill
There is no question in my mind but that the controlled slip (not wing-down!)

This'll be good. Please explain the wings-level controlled slip.
http://www.pprune.org/images/statusicon/user_online.gif http://www.pprune.org/images/buttons/report.gif (http://www.pprune.org/report.php?p=8742046) http://www.pprune.org/images/buttons/reply_small.gif (http://www.pprune.org/newreply.php?do=newreply&p=8742046&noquote=1)

A question of terminology. "Wing down" suggests you could be placing wingtips or pods in jeopardy whereas a correctly flown controlled slip landing should see bank angles of the order of no more than 2 degrees.
Similarly it amazes me that any professional pilot can use words like "kick" in connection with control of an aircraft in the flare. What do you think would be the effect in Row 40 if your student takes it literally? (Yes, someone did do it to me in a 757!)

The single greatest disadvantage of the last-moment de-crab is that, if mis-judged, it leaves the aircraft drifting downwind and the pilot running out of ideas (particularly if carrying excessive speed). A common reaction is to push the nose down in an attempt to get on the ground. If this means that the touchdown is nosewheel first, it can cause serious damage to the airframe.

While I eventually did acquire the ability to de-crab early in my career, there is no question in my mind that controlled slip builds student confidence earlier and is more likely to lead to successful outcomes.

Why accept that touchdown with 5 degree crab angles is OK if you can ensure a smooth normal flare and touchdown on centre-line?

[scotbill]

Glendalegoon

I have yet to find a runway where you could not use controlled slip. The whole concept is based on maintaining runway centre line and gradually intoducing opposite aileron and rudder in the last 100 feet or so. Even displaced centre lines allow a normal approach eventually.

Please explain what is different about Washington?

[ACMS]

Yep I've said it before in this thread and I'll say it again......

I only introduce the "de crab" slip during the flare, I don't fly a sideslip approach.....I've seen it done in Jets and I didn't like it.

I've flown the IGS in HK with a gusty crosswind lining up at 500' on approach around the corner between the roof tops in a 744 at 160 KIAS during a Typhoon.

Then used the Boeing trained "de crab" manoeuvre in the flare

I'm still here alive and the Aircraft ain't bent.....

[bubbers44]

McNugget, a quick check of FAR 61 says a multiengine rating with no centerline thrust limitation can be given in any aircraft that has a VMC. The Lear has a VMC as does the MD80 and B727.

[Case One]

Still not seeing the requirement for, or advantage of this "upwind asymmetric thrust" concept (or whatever you wish to call it). Could one of the virtuosos of this technique kindly explain it in detail? Is it only peculiar to some types?

[vilas]

Titaniumwings
You started the thread in relation to A330 and was applicable to Airbus FBW in general. Now it has drifted out of that parameter and now individual techniques and quirks are being discussed. None of which is applicable to Airbus. I hope you have already switched off.

[titaniumwings]

I have big ears and always like to listen. Now I am listening to aviators all around the world the comparing the pros n cons of the side slip vs crab-decrab method. The passion of everyone loving their art is really heartening and invigorating. Always love listening to aviator's stories and their craft.

I was taught both when I first started flying. I also read the pros n cons of both. I saw both being practiced in the Boeing and many other aircrafts but just to have a particular discussion on Airbus as its FBW has certain characteristics which make the side slip method quite a topic for discussion.

This is especially so because both the side-slip and crab-decrab method are predicated in Boeing FCTM but Airbus specifically predicate crab-decrab method in their FCTM without any restriction or limitation being mentioned anywhere else. I do not have a problem with Airbus recommendation but for those who ever wish to try the side-slip method on Airbus, an understanding of the aircraft Law would be beneficial to the action-reaction/see n react that thing pilot does. In the real world not thoroughly understanding this part may not result in critical consequences. I just like to know the aircraft intimately. BTW I used the crab-decrab method but I don't judge those who use side-slip. I like to keep things simple and just follow the recommendations whenever I can but when someone asks me I wish to be in a position to tell yes and no with the corresponding reasoning and explanations especially technically.



ps: But if someone has time and free then consider the question that I last posted in #44. I believe there is a group which has the following interpretation:

In a steady state crosswind with Airbus FBW Lateral Law the roll rate is ordered by the side stick. Computer will order rudder output for turn coordination (centering the "ball") and yaw damping. Hence in wings level condition and without sidestick input, 0 roll rate will be ordered.

Now here is the key: Will this order be continued when pilot give a rudder input. In other words will the aircraft's computer order the rest of the control surfaces to give 0 bank as the sidestick still orders "0" roll rate? From what I read, I believe some people believe this and expect the wings to be level when they input the rudder in decrabbing. (The other interpretation will have the pilot putting in a coordinated aileron with the rudder input when decrabbing).

Should this be the case then consider when you are turning the aircraft with 5 degree angle of bank then you neutralise the sidestick. Aircraft will order the rudder accordingly to coordinate the turn. Now you put in rudder input, will the computer still order the rest of the control surfaces for "0" change in roll rate to maintain your 5 degree angle of bank? (some may even take it as "in-between" the 2)

In the real world, wind is not constant and pilot will do whatever is necessary(inputs accordingly) to keep the heading down the runway and aileron correspondingly to keep the aircraft on the centreline.

Nonetheless if the interpretation of the aircraft reaction is valid then there is a bearing on the "way" the aircraft can be "used" to the the sideslip method. This thread is started by the comment that I have heard some people saying that Airbus can't do sideslip method for landing, by that I mean side-slipping the aircraft at 400'. For the purpose of this discussion let's simplify the comparison between crab-decrab (as most may have known it) and sideslip to mean sideslipping starting at short finals of below 400' but above flare height. It is also clear to me that most (if not all) know how to fly their aircraft and do their jobs. I and we are not contra-recommending any change in techniques, just a simple exploration of the aircraft that we love.

Thank you for your time and consideration.

[sonicbum]

To cut a long story short follow the manufacturer's instructions and as many have already stated don't try to reinvent the wheel.

[sonicbum]

In other words will the aircraft's computer order the rest of the control surfaces to give 0 bank as the sidestick still orders "0" roll rate?

Yes. When you decrab as you know one wing will travel faster than the other and therefore generate more lift which ends up in induced roll. For crosswind up to 20 kt the normal law will manage to keep wings level or almost level by coping with the zero roll rate demand. With winds speed greater than 20 kt the induced roll during the decrab will have a greater intensity and therefore the pilot is required to adjust the wings by giving some side stick inputs. With very strong crosswind it may be quite challenging to coordinate it without risking to have one wing down during the flare, as you can see here.
Airbus tells you that 5 degrees of crab are still acceptable at touchdown to cope with the above mentioned difficulty. Now the question is : do you remember how many degrees of crab you had during your last crosswind landing ? Probably the answer is no, as I believe that you are not watching your ND at that stage, nor is your other CM. If something happens and findings reveal that you were well above these 5 degrees, you can have an interesting debate with whoever is concerned. Finally decrab the airplane following Airbus specs and if it is not feasible then you may want to explore the function enable alternate. :8

[vilas]

titaniumwings
Try to do an auto land in the SIM with 20KT crosswind and you will get all the answers. First the auto flight system uses crab and not slide slip, second when it decrabs after flare wings are maintained level by spoilers and aileron activation. I think that is enough to explain the design philosophy and the SOP.

[glendalegoon]

scottbill


what is different about washington, landing to the south, is that final approach lasts about three seconds. a very low altitude turn to line up with the runway is required after following the Potomac river for about 6 miles.

if you can obtain a copy of the river visual approach to runway 19 or view someone's video, you might understand.

all the best

CASE ONE

if you use the upwind power technique,/ assymetric/differential thrust, you are making the engine do the work of the rudder...and that gives you more rudder for the instantaneous corrections sometimes required. does that make sense?

[vilas]

Airbus asking you to land with 5 degrees crab is another indication that the design does not prefer wing down. You don't need to look at ND to touch down with some crab, looking at the centre line ahead will suffice. The problem in landing with crab is the side load. If you land with drift it will still impose side stress. I remember in 747 classic it was recommended to land with crab on wet runway. On wet runway the aircraft initially skids sideways that reduces the side stress and then the CG position straightens the aircraft.

[ACMS]

Vilas---I think you just proved our points. The A330 autopilot can only handle 20 kts of crosswind, which is not a lot. Up to 20 kts the wings can be kept level in the de-crab during the Flare if it's done correctly and you won't need much if any Aileron input. Yes that is how the Autopilot does it in an ideal world.
( then again how do you really know how much Aileron input the A/P makes in the flare as the Sidestick doesn't move and you can't watch the F/CTL page!! )

But at the end of the day in the real world ( not a sim ) you may need to land one wing down in a decent crosswind whilst hand flying.

AS PER THE AIRBUS PUBLISHED FCTM I quoted way back.

Can we move on to something else now?

Close the thread it's running around in circles chasing it's tail.....:ugh:

[vilas]

ACMS
I am talking about a Sim demo and you confirm the behaviour of normal law on the F/CTL page. However as you say in real life you stick to centre line if required by banking into wind.

[Goldenrivett]

Hi sonicbum,
With very strong crosswind it may be quite challenging to coordinate it without risking to have one wing down during the flare, as you can see
The Lufthansa aircraft landed on the down wind wheel first, lost half their aileron control, and continued to roll despite full side stick.

See pages 39 & 53 of A320_Hamburg-Crosswindlanding.pdf (http://www.bfu-web.de/EN/Publications/Investigation%20Report/2008/Report_08_5X003_A320_Hamburg-Crosswindlanding.pdf?__blob=publicationFile)

"Touchdown
• The aircraft was 4° left wing down at the time the left main landing gear made contact
with the runway
• The horizontal acceleration was 0.17g to the right, the vertical acceleration was 1.68 g
• The rudder was deflected about three quarters of maximum throw to the left. At this time
the yaw rate was about 6° per second.
Between contact by the left main landing gear and contact between the left wingtip and ground:
• The aircraft rolled towards the left
• Both the captain and co-pilot gave sidestick inputs to the right
• The left wing down attitude reached a maximum of 23°, whereupon the left wingtip
touched the ground
• The rudder was deflected about one third of its full throw to the right"

"The system was so designed that when in lateral Ground Mode the ailerons/spoilers kinematics are modified as a function of speed, in the sense to reduce the maximum available ailerondeflection by half (at high speed: > 80k)t. This was also confirmed by the Flight Data Recorderparameter traces, in which aileron deflection was reduced to about half of full travel in responseto full sidestick deflection."

Oops!

[vilas]

Goldenrivett
There was a modification done by Airbus after this accident.

[Goldenrivett]

vilas,

If you are referring to "Evolution of ground spoiler logic" Airbus%20Safety%20First%20Mag%20-%20Feb%202010.pdf (http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presentations/Airbus%20Safety%20First%20Mag%20-%20Feb%202010.pdf), then that mod was to reduce the height of a heavy landing bounce.
It does not restore full aileron control.

[scotbill]

I agree that this thread has probably ended in the usual stand-off between entrenched closed minds on both sides. It can do without this sort of thing

scottbill

what is different about washington, landing to the south, is that final approach lasts about three seconds. a very low altitude turn to line up with the runway is required after following the Potomac river for about 6 miles.

if you can obtain a copy of the river visual approach to runway 19 or view someone's video, you might understand.Thank you for the condescension but perhaps allow that after 40+ years in aviation, this does not look like a task for supermen only. Looks like fun, though.

"Three seconds" - really?
The controlled slip I discussed is best initiated at about 100 feet (to allow for low-level windshear). 50 ft perhaps - so long as it is set up before the flare. On Boeings, the important bit that so many get wrong is that the control wheel movement to set the aileron input becomes a new datum which has to be maintained throughout the flare and initial landing run. See-sawing of the ailerons must be avoided.

Could that be relevant to the application of the technique on Airbuses?

[glendalegoon]

scottbill

DCA is not for supermen. But, in my 40 plus years in aviation, I don't see anyone doing the sideslip method at DCA.

[hikoushi]

If you enjoy the approach into DCA, try a "channel visual" approach to 08L at PHNL with a screaming crosswind sometime, or better yet the "Keehi Lagoon" circling approach to 26R the local pilots use on strong southerly-wind days. Thank the China Airlines flight that buzzed downtown Honolulu on a visual approach for getting that one on the books years ago. Watched from Lagoon Drive off the end of that runway many a time over the years as DC-9's and 737's rolled wings-level around 300 or 400 feet on final with a 20 or 25 knot tailwind on base-leg that now becomes a direct crosswind. Many times with many techniques. Most roll out in a crab and kick it strait anywhere between 50 and 100 feet, slip the rest of the way. Some kick it out in the crab, some don't kick it out at all, etc etc etc.

All those techniques seem to work just fine. As long as it is in accordance with the flight manual and SOP, use whichever method works for you. Bottom line, just land on the centerline, keeping the airplane's inertia along that line and the wheels pointed reasonably close to the same direction the airplane is moving.

[bubbers44]

Teaching basic crosswind landings I started with an early sideslip to show how to keep the aircraft straight with the rudders and correct for crosswind with ailerons to stay on centerline.

As they became more experienced I had them delay until late into the flare to make one fluid coordinated rudder and aileron application and then make small adjustments to keep on centerline with no crab. The technique is comfortable for the passengers because you aren't kicking it out but smoothly coordinating the transition from crab to touchdown.

[vilas]

titaniumwings
The thread is split in three parts, cross wind landing techniques in general, individual ideas and lastly Airbus procedure. As far as you are concerned only the last applies to you. I recommend you obtain and read Airbus document 20th Fight safety conference LATERAL RUNWAY EXCURSIONS Cross wind Design and Operational Considerations which was held between 24th and 27th Mar2014. The salient features of that are follow auto pilot logic i.e.
1. Wings level and crabbed approach
2. Flare
3.Decrab
4. Ground control
In high cross wind and especially contaminated runway partial decrab may be required using crab angle and bank angle, use roll control only if required to maintain aircraft on centre line.
In the19th safety conference in gusty wind conditions use of ground speed mini(ATHR in managed speed) is recommended.
If you do something else as suggested by some people here and have an incident you will find yourself a very lonely man.

[MD83FO]

http://www.skybrary.aero/bookshelf/books/871.pdf

[Amadis of Gaul]

I agree that this thread has probably ended in the usual stand-off between entrenched closed minds on both sides. It can do without this sort of thing


Yeah, but consider how much knowledge did we the great unwashed Airbus drivers just gained from the highly qualified internet aerodynamicists on this thread. The learning experience has been invaluable.

[vilas]

MD83FO
Did you say Airbus? I didn't notice this word any where.

[Aztec Kid]

Several years ago, when attempting to gather more detailed information regarding the Airbus autoland logic, than is currently available in the FCOM and AMM, an Airbus flight control engineer shared the following:

The autoflight system will utilize a crab to compensate for a crosswind until approximately 45 feet. At this point, the align control law engages. The goal of the align control law is to reduce the crab angle, while maintaining the track of the runway centerline. For the A340-500/600, the autopilot will decrab up to 70 percent of the initial crab angle, with a limiting decrab of 7 degrees. According to the engineer, up to a 7 degree bank angle will be used to counter any drift during the decrab.

It was decided to limit the maximum crab angle during touchdown to 3 degrees. Combine that 3 degree angle with the limiting decrab of 7 degrees, yields a maximum crab angle prior to the engagement of the align control law of 10 degrees. This is what was used to determine the maximum crosswind limit of 23 knots, for an autoland in the A340-500/600.

As vilas has pointed out, Airbus has produced several presentations and documents devoted to crosswind landing techniques. While these sources give a reasonably good explanation of how to deal with crosswinds in the Airbus, I do believe there is room for additional clarity.

There are several potential negative transfer issues for pilots who are transitioning from traditional aircraft to the Airbus. The crosswind landing is one of these potential problem areas. As pilots flare and apply rudder pressure to remove the crab, they often apply and hold an opposite roll input. This leads to a greater bank angle than desired. Attempts to then reduce the bank angle typically are made with sidestick inputs that are too large. The result is PIO in roll, especially in gusty conditions. This type of PIO during the flare has been captured in numerous videos of Airbus crosswind landings.

When a bank angle is required to control drift, only a very small roll input is required until the proper bank has been attained. Once this bank angle (no more than 5 degrees) has been establish, the sidestick roll input is neutralized. At this point you are accomplishing a slideslip, but you are not utilizing the “cross control” technique of a more traditional aircraft.

I have found this thread quite interesting, and hope that it continues.

[titaniumwings]

Aztech Kid,

Really enlightening information. Thank you so much for sharing.

"Incidentally" my SOP requires the call of "BANK BANK" if the bank exceeds 7 degree for landing (for A330). I can see clearer now.

Appreciate the sharing guys!!!

[pontifex]

Aztech

You may not be utilising the "cross control technique" but the aircraft is!

[Aztec Kid]

That is precisely my point. The flight control surfaces are “crossed”, even though the control inputs are not. That is why pilots who have extensive experience with crosswind landings in aircraft with traditional flight controls, often need time to get accustomed to the control inputs required when they transition to the Airbus.

[titaniumwings]

This thread is started with the basic question of:
Can Airbus utilize Side Slip Landing Technique? and if not Why?
(side slip landing technique for this discussion means to establish in a side slip prior to flare)

Though it is reemphasized that Airbus recommends crab-decrab technique for landing in its FCTM. The reasons for that are possibly in this thread. These valuable explanations may ease the minds of those who are transitioning from the side slip technique.

Once again many thanks to those who had contributed to the search for this answer, especially the explanations. I have gained much. Thanks also to those who had given their inputs for the use of the different landing techniques and why not the other. I learn no less.

Many has and will continue to chant the mantra, the moment you cease to learn is the time you cease to fly.

Cheers to the camaraderie of aviators.

[titaniumwings]

vilas,

Thanks for your summary and views. Not able to source for the Flight Safety Conference document yet. Any chance you can share it?

A good suggestion to see how the "aircraft" works by looking at the sim. As you had mentioned the autoland pilot will centre the heading and apply the aileron to level the wing for crosswind landing.

A question from this. Some has mentioned that they expect the aircraft to maintain wings level while they centre the nose as they are not demanding any change in the roll rate and expect the aircraft to keep 0 roll rate by itself (meaning the computers will order the necessary aileron output).

We know the aircraft outputs aileron for wings level but would this be done by the computer or is it expected from the pilot/autopilot? In other words, while manual land, when the pilot centre the heading would he need to level the wing or would the computer do it? (This is with reference to crosswind value which does not require a partial side slip at touchdown). Could you please verify for us with your ideal controlled simulator environment?

Thanks very much.

[Gryphon]

Vilas,

What MD83FO posted is a document from Flight Safety Foundation (ALAR), but a copy of it has been reproduced by Airbus in "Getting to Grips whith Approach and Landing accident reduction" Briefing Notes "crosswing landings".

I cannot provide a link, but it won't be a problem for you. :)

[vilas]

Gryphon and titaniumwings
Thanks I have that entire series and have read it. It is old. The safety conference I quoted is March 2014.
titanium wings, as quoted by ACMS in post 5 when you decrab you do not require aileron as the yaw will not cause roll because the FBW will hold level yes even in manual flight. Off course to do that it will apply aileron, spoilers but you don't have to apply. You only apply aileron if required to keep on the centre line. I am not able to post the conference report. Sorry about that. Lastly I would add that it is a very easy aeroplane to fly but not that easy to understand because of it's computerised nature. So it is safer to stick with manufacturer's recommendation than devise your own procedure because you do not have access to all the software that goes into the design and even it were available most of us would clueless unless you have software background.

[vilas]

Goldenrivett
I mentioned that a modification was done to improve the aileron effectiveness but I couldn't locate it. Here is that Mod after Hamburg incident of wing scraping the runway.
The reduced effect of controls was not documented in the system description and was unknown to pilots or the training department.
By now the Flight controls laws logic has been modified with a modification of transition from flight to ground lateral law. This improvement has been certified in 2012 in the ELAC standard L96 and is available through Service Bulletin ref 27-1225.

[Goldenrivett]

vilas,
Thanks for the update. Do you have any more info on what the mod actually does?

[vilas]

Goldenrivett
Unfortunately I have lost access to the MOI. But what I quoted is mentioned in the inquiry report. If you google it you will find.