Use Of Rudder In Large Transport Category Airplanes

[NGjockey]

I just read a interesting IFALPA briefing leaflet titled "Use of rudder on Boeing aircraft". One conclusion towards the end of that article was that (quote) "The rudder in a large transport aircraft is typically used for trim, engine failure, and crosswind takeoff and landing." In other words, do not step on the rudder pedals during normal operations except when required in crosswinds during takeoff or landing.

At this point I would like to clarify that I am familiar with the AA587 accident, its reasons and conclusions. I agree that the incorrect use of the rudder was a causal factor for the loss of control there, and I want to stress that I do not want to start another discussion about the inappropriate and/or excessive use of the rudder in large jets.

What I would like to know is your opinions and experiences regarding the subtle use of the rudder in situations where it would be perfectly warranted in smaller aircraft types, such as after departure or in a traffic pattern. What I could so far gather from my fellow colleagues out on the line is that the vast majority of pilots shies away from using the rudder like the devil shies away from holy water, and understandably so when reading that even the manufacturer recommends to do so (as mentioned above). In most situations at normal speeds during climb, cruise and descent that makes perfect sense to me as well, but there are some situations where I would like to question this mindset. For example, when flying a SID which requires a large turn at low speed after departure the slip/skid indicator in a B744 shows a considerable deflection (with or without the autopilot engaged). The airplane is actually in a sideslip since the aerodynamic forces at low speeds are not strong enough to prevent the tail from "hanging" down into the bank. This is not an issue at higher, "normal" speeds, but at low speed and low altitude it kind of goes against everything I've learned back in the days on the single engine trainer. The more uncoordinated the airplane flies, the larger the turn radius will become, and to some small extent there will also be a little bit of performance loss (even though I will admit that this should have a negligible effect in a all engine operating condition).

So, in airplanes where the autopilot does not control the rudder directly, would it really be so terribly wrong to GENTLY and SLOWLY add a little bit of rudder in such situations until the slip/skid indication indicates coordinated flight again?

I often hear the argument " Don't you know what happened to that Airbus in New York?", but like I said above, a gentle and appropriately slow rudder application has nothing to do with what happened with AA587. It would be the same like saying that we should not use the yoke to control pitch during approach because we might pull back too hard, stalling the airplane or overstressing it at higher speeds. As highly trained pilots we should all be able to judge the amount of control input required to maintain our flight path, and if we aren't, what does that say about our abilities to safely fly the airplanes we are rated on?

[flyfan]

Not taking into account any manufacturer recommendations or SOPs, I tend to agree with your point - especially considering the massive rudder deflections needed with an engine out, there shouldn't theoretically be any problem in using normal rudder deflections on takeoff / approach. The airplane should be designed to be able to handle that, as long as you're not doing left/right full deflections with 300+kias.

Nonetheless, I never noticed any significant slip on the NG yet so definitely no need for rudder...will have a look next time I fly (so expect that to be in 5 years or so :} )

[mustafagander]

Spoilers on the down going wing are sized, so Boeing tells us, to eliminate any need for rudder. And it really works as advertised.
Rudder is not used in normal flight manoeuvres.

[anson harris]

In the aircraft I fly (747) the yaw damper provides turn co-ordination without causing any movement of the rudder pedals. I think that's fairly common across the Boeing range. The turn and slip indication on the PFD is (so I'm told) not especially accurate. Quite honestly I don't see any need to overcomplicate matters. I only touch the rudder pedals during taxy, crosswind takeoff and landing and in the sim during an engine failure. If Boeing says don't touch, I don't touch.
When I have deviated from SOPs in the past, I try to ask myself whats in it for me. The answer is often nothing.

[Check Airman]

On my current plane (A320), my feet are on the floor once airborne. The yaw damper does a pretty good job. I’ve only ever needed to use the rudder on one airframe.

[BraceBrace]

The slip & skid indicator is the most unreliable instrument (together with the compass) on larger transport aircraft. The YD keeps it coordinated, there is no need for rudder at all. On top, slipping an aircraft of this size (jet engines, swept wings) creates extra hazards you don't want to learn in reality (disturbing the intake airflow for the jet engines, different stall characteristics in low speed turns).

Rule n°1: don't fly a jet like a Cessna, it will get you killed. Especially in low speed. It's the start of all line training for pilots flying swept wing jets for the first time. Never ever "tighten the turn" with rudder in low speed on a swept wing.

[PEI_3721]

Most large aircraft have an integral turn co-ordination function within the yaw damper to minimise the lateral acceleration by applying a small amount of rudder in turning flight
The co-ordination system is generally independent of the AP - a stand alone system, or if part of an integrated flight control system, it would not depend on AP engagement.
In an aircraft with well optimised turn co-ordination and yaw damping there should be no need to use rudder in normal flight. Any manual rudder input could confuse the system, temporarily, or be out of phase, resulting in even more acceleration.
The quality of turn co-ordination relates to the aircraft characteristics, control system (e.g. spoiler for roll), flight conditions, and system fidelity; an ‘optimised compromise’, there may be some transient deviations when rolling, which reduce, to become balanced in a steady turn.
Note; check which parameter the ‘slip/skid’ indicator uses and its scaling, - lateral acceleration?

[Switchbait]

Pure gold 🤣

[tolip1]

I think we should listen to Airbus, Boeing and company SOPs over a stranger on Pprune.
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[lomapaseo]

I don't understand?? I thought this was a discussion and not rule based no matter who posts

[Timmy Tomkins]

On the DHC Dash 7, full rudder authority was not available until some flap was selected; are there any similar systems on the Boeing fleet?

[pattern_is_full]

What I would like to know is your opinions and experiences regarding the subtle use of the rudder in situations where it would be perfectly warranted in smaller aircraft types, such as after departure or in a traffic pattern.

Depends on how you define "smaller aircraft types."

It is definitely the case that propeller aircraft suffer from asymmetric engine and prop yaw-control effects that are neglible in turbojet/fan aircraft.

P-factor, engine torque, gyroscopic precession, and (in singles) spiral propwash impacting the entire tail-fin assymetrically, all combine to make prop aircraft yaw, especially during climb-out (high nose angle). And the smaller the aircraft (relative to engine power and prop mass) the greater the effect.

Unless, of course, the aircraft is a multi-engine and the manufacturer goes to the trouble and expense of installing engine(s) on one side that are "backwards" (counterrotating) and balance the yaw forces (Piper Seminole twin-trainer, for example).

See also: "Critical engine" - a problem very important to prop fliers if they lose an engine, but generally non-existent in flying jets.

[BraceBrace]

I have flown several Cessna jets, and I was not killed.

Lol. Good for you.

"As highly trained pilots we should all be able to judge the amount of control input required to maintain our flight path, and if we aren't, what does that say about our abilities to safely fly the airplanes we are rated on?"

The answer is easy: highly trained pilots learn to fly the aircraft they are flying as explained by the constructor, it's part of being "rated" on the aircraft.

Better?

[NGjockey]

@ BraceBrace:

I beg to disagree. On the type I fly (B744), the slip/skid indicator derives its information from the IRU, which is also the source for heading, wind, track angle, drift angle and ground speed information. That is information we usually put quite some significance on, so why would only the slip/skid information be inaccurate enough to be allowed to be dismissed? Boeing (and all other manufacturers) would get into hot water if they deliberately installed an indicator which would provide misleading information, especially in the middle of the PFD, which is the most important display of all.

As to your argument that I don't want to learn about the effects of the extra hazards that a slip would create on an aircraft of this size, let me assure you that I couldn't agree more. The point is however, that the aircraft already is in a slip in a high bank angle low speed turn, and that is why I have raised this topic here. This is not about trying to "tighten the turn", this is actually about getting rid of the slip and achieving coordinated flight. According to the slip/skid indicator the yaw damper does a pretty bad job at coordinating the turn at low speeds. As the airplane accelerates into higher speed ranges turns get more coordinated because of the increasing velocity of the airflow around the rudder. Just have a look at the slip/skid indicator at low speeds and then at high speeds, using the same bank angle. The difference might surprise you.

[blind pew]

In the old days when pilots tried to do a greaser we had a captain, who if he thought you had accidentally got it right in spite of trying extremely hard, would put a large boot of rudder in during the flare and watch how you coped with the secondary effects with a highly swept wing.
Still here to tell the tail.

[NGjockey]

@ BraceBrace:

True. Also true is that part of being rated on an aircraft includes for example being able to perform crosswind takeoffs and landings on slippery runways. If you read the FCOM or FCTM you won't find any information about how many inches of rudder or control wheel input you will need exactly for a particular crosswind or a particular mass. You will apply inputs as needed according to your experience, and that is what I wanted to state with my argument about being able to judge the amount of control input required as highly trained pilots, in any phase of flight.

[Vessbot]

Is the ball showing a slip just during the roll-in, or also during the constant-bank, established part of the turn after stabilization? What about the rollout?

[tdracer]

On the DHC Dash 7, full rudder authority was not available until some flap was selected; are there any similar systems on the Boeing fleet?
IIRC, rudder authority is reduced at higher airspeeds, but don't recall specifics.

[Vessbot]

Could this be the long-tail slip (https://www.av8n.com/how/htm/yaw.html#sec-long-tail-slip) effect happening? In a turn, the airflow is curved but the fuselage is straight, so the airflow can be aligned (zero slip, or beta, angle) either at the tail or at the CG (or wherever the IMU is installed) but not both - you have to choose one or the other. So, if the inclinometer shows centered, that means there is a slip angle at the tail. Or, conversely, if there is no slip at the tail, there is slip at the CG (therefore side force, therefore off-center inclinometer). Usually negligible, but could show up in a long enough airplane in a tight-enough turn. And a basic yaw damper cancels yaw rates but not steady-state conditions of off-center yaw, so it allows this condition to persist.

[KayPam]

Airbus has automatic turn coordination, but if it happened for some reason to not work, I don't see any reason why not to use the rudder and do the job.
Sideslip should be demystified, I'm practically sure that Airbus and Boeing have very good models for simple movements around the yaw axis, why not do it in the sim ? Do a little dutch roll to see how it handles.

On the fun side, using the rudder in an A320 type will create an artificial wind on the ND. Try it and see for yourself :)

[RetiredBA/BY]

IIRC, rudder authority is reduced at higher airspeeds, but don't recall specifics.

Yes, it was called the rudder ratio system.

I see no reasons (because there aren’t any ) to use rudder on a large jet, x wind, engine failure etc. excepted . period.
Chipmunks, Tigers, Cessnas and Pipers are different.

[B2N2]

You use the rudder when it’s time for you do some pilot stuff aka when it’s appropriate.
From small to large all aircraft fly the same, you just don’t fly them the same.
Low speed regime use the rudder pedals, high speed regime you don’t.
The outboard ailerons lock out at 235 kts, I’d say that’s a pretty good clue from Mr Boeing.

[megan]

To add to Vessbot's post, on a large aircraft the radius of turn made by the extremities (nose, tail) will differ to that of the CoG and have noticeable effects, compared to a small aircraft such as a Chipmunk. If the slip/skid was of a self contained type, as used on light aircraft, and installed in a large aircraft cockpit centering the ball would mean everything aft of the cockpit would be in a skid. IMHO

[CCA]

As others have said the so called slip skid indicator is very sensitive and shouldn’t be used like on a light aircraft.

Boeing refers to the Slip/Skid as body lateral acceleration.

I’ve always surmised that it’s slip/skid indication in a turn is the fact the IRUs are some distance forward of the aerodynamic centre of the aircraft.

The 747 in particular is very good inherently for turn coordination and does not need “help”, handling the big jets has a good read.

One thing that isn’t really talked about is the large amount of roll induced by the rudder which can cause instability.

3 large rudder inputs:
1. final
2. Flare
3. During the go around!

https://youtu.be/oRScivHIH10

[vilas]

IIRC, rudder authority is reduced at higher airspeeds, but don't recall specifics.
Even Airbus does the same. It is called rudder travel limiter.

[anson harris]

The outboard ailerons lock out at 235 kts, I’d say that’s a pretty good clue from Mr Boeing.
If "Mr Boeing" wanted you to read something into that, I'm pretty sure he'd tell you.
Secondly, if the turn co-ordination provided by the 747 yaw damper was so poor, wouldn't everyone in the cabin be feeling accelerations, other than straight into their seats, every time we go around the corner? As well as flying the thing, I've spent a fair bit of time in the cabin and can't recall my drink ever being spilt while turning, even at low speed.
I think the video of the podstrike shows exactly why a lot of caution is required every time the rudder pedal is touched in the 747. The associated roll is significant and I'd be lying if I said it hasn't surprised me at least once. Hopefully I learned from it and got better the next time. But then again, I tend to follow the guidance that it really doesn't need any rudder until just prior to touchdown and on a wet runway I would say it's only really required once you have main gear touchdown - you can see in that video that the rudder is being hammered at about 50 feet.

[MadamBreakneck]

Rule n°1: ... Never ever "tighten the turn" with rudder in low speed on a swept wing.

Lordilord, I wouldn't even let student pilots do that in a microlight, swept wing or otherwise!
(No experience worthy of mention in anything heavier, so p'raps misunderstood)

[FullWings]

Can you use the rudder on large jet transports in the same way you might use it on a light aircraft? Yes. Do you need to? No, not really, outside of asymmetric conditions or deliberate crossed controls. I admit to a bit of top rudder turning visual finals with an empty aircraft, just for the fun of it, but I don’t think it would impress passengers.

On modern jets, especially FBW ones, there are all sorts of things going on underneath the skin that obviate the need for rudder inputs in normal flight, so you’ll just end up fighting those systems...

[Koan]

They took the Boeing slip/skid ball off our 737NG panels years ago.
There is an indicator under the roll pointer on the PFD when you need it.
Some sim sessions left me sweating and thinking I need more leg work at gym.
787 much nicer.

[farefield]

I had a mate who used the rudder a lot in a VC10 up at 30 odd thousand feet. Back and forth or should that be side to side? it went. Fortunately it stopped once he'd got the probe in the drogue.:ok:

[filejw]

In the old days when pilots tried to do a greaser we had a captain, who if he thought you had accidentally got it right in spite of trying extremely hard, would put a large boot of rudder in during the flare and watch how you coped with the secondary effects with a highly swept wing.
Still here to tell the tail.
He would get away with that maybe once at the place I worked....

[B2N2]

you can see in that video that the rudder is being hammered at about 50 feet.

That’s a rudder defection to the Left with a pod strike on the Right.
They encountered windshear at low altitude.

[CCA]

WRONG and why rudder should only be used for crosswind correction and engine failures. If the aircraft had a fin out the top and the bottom you’d only get yaw and secondary roll from the wing but there is a significant roll from the top mounted fin when rudder is used inappropriately.

That fin has more wing area than one side of a 757 and they just deployed the entire trailing edge to full deflection.

[anson harris]

That’s a rudder defection to the Left with a pod strike on the Right.
They encountered windshear at low altitude.

Yes, I realise that. What I'm hinting at is that maybe there's some misunderstanding of how to use the rudder during a crosswind landing.

[BraceBrace]

@ BraceBrace:

True. Also true is that part of being rated on an aircraft includes for example being able to perform crosswind takeoffs and landings on slippery runways. If you read the FCOM or FCTM you won't find any information about how many inches of rudder or control wheel input you will need exactly for a particular crosswind or a particular mass. You will apply inputs as needed according to your experience, and that is what I wanted to state with my argument about being able to judge the amount of control input required as highly trained pilots, in any phase of flight.

Yes, but that is training. I sometimes allow people who are scared of crosswind landings in line training to go (established on the ILS with runway in sight) low wing and out again on the approach. It gives them a sense of how much rudder input is required (but it is REALLY important to state that rudder input is gentle & singular and then you hold the rudder in that deflection - never "play" with it) AND how it effects your aileron requirement. The secondary roll effect due to rudder is always there, always, and you have to give it time to show up.

I don't know if it is a common thing on turboprops, but when people come in with turboprop experience they will often "fiddle with the rudder" on final. Some of the aircraft I fly are old classics with not too symmetrical thrust and some rudder trim requirements, and that's always been an excuse for them for the negligence of the secondary roll. It shouldn't be if the thrust is equalized and the trim was set properly. They will hardly ever be able to stabilise the aircraft with the rudder tickling because they end up correcting secondary roll all the way down.

Rudder is "designed" to cope with engine failures and therefore very powerful for "normal" steering. Which is why once the flight controls become more effective (flaps up) or engines less powerfull (high up), the rudder force is generally reduced to more acceptable levels. If you look even look at non-normals, Boeing is very cautious in advertising the use of rudder. Even in manual reversion on the 737, Boeing doesn't stop you from using rudders, but it emphasises not to overcontrol it and be really gentle. Because you always create secondary effect you don't want. Even in an approach to stall - or stall recovery or upset recovery, Boeing says not a single word about use of rudder. The reason is easy: DON'T, as the secondary effect is the nastiest backstabber you can find.

Boeing designed an aircraft where you don't need to use rudder except in a certain set of situations and that is trained for. And I'e never felt uncoordinated in a turn (within the limits of course, but heck I don't even like 30° bank to be honest, 25° in manual flight should get you everywhere as the maneuvering speeds allow you)

BTW: it's one of the hardest things to "de-learn" for the turboprop guys, because there have been many cases where I said "but you were steering with your feet" and they said "no". I truly believe them as there have been too many. They do it without even knowing. Which is why I emphasize "no rudder unless a very specific situation" so hard in this discussion, and the idea you really have to put an effort in "learning the aircraft you fly".

I know the document that started this thread. The background is not about good or bad pilots, it even discusses people with plenty of military background who are very capable pilots. They have used rudder on carrier landings, to pinpoint the nose in dogfights, etc etc... but the main goal here is: learn to use your aircraft as the guys who designed it tell you to.

Tapping the rudder to coordinate a turn "more" does not make you a better pilot (which is also a statement that was posted in the thread starter), as subconciously you might be learning yourself dangerous stuff. Don't tap the rudder in a turn. Learn yourself the right way to fly the aircraft, don't go out and tell the other guy he's not flying correctly as he IS doing it the correct & safest way.

[CCA]

Nicely put, like you say you can feel the crew who still fly it like it needs rudder assistance, small roll inputs with small rudder inputs. The problem will be on those gusty days with large roll inputs required then coupled incorrectly with large rudder inputs which can get ugly very quickly but will be blamed on the weather.

[KingAir1978]

In the old days when pilots tried to do a greaser we had a captain, who if he thought you had accidentally got it right in spite of trying extremely hard, would put a large boot of rudder in during the flare and watch how you coped with the secondary effects with a highly swept wing.
Still here to tell the tail. I see what you did there...

[Schnowzer]

Having flown big Airbus, the fear seen when discussing the use of the rudder is sometimes irrational. The manuals say it is available for crosswind landings and engine failures but most crew think it is a one off input rather than an adaptable flight control. Obviously it is dumb to put a large input above approach speeds but the latest aircraft even protect dummies from doing this by reducing the rudder authority as speed increases.

I believe if you get a float in a large aircraft and the fuselage has been aligned too early, the only way to prevent lateral drift is with, as you say, the “subtle” use of rudder. Using aileron when the inner engine is on the runway edge is fraught with danger. Obviously if you are going to miss the TDZ, go around and have another go but a squeeze of rudder to prevent drift is eminently sensible.

All that said it is madness to try and coordinate turns when there is a decent flight control computer between the stick and control surfaces.

[Pugilistic Animus]

I've used the rudder to fly runway heading from an initial track, on instruments and VMC. Of course, the runway as a reference will most likely be gone by then.

[B2N2]

anson harris

So go on, teach us how to use the rudder in a crosswind landing when encountering windshear.
We obviously need it.
I’d love to hear.

[vilas]

In airbus aircraft yaw dampers automatically provide turn co-ordination and yaw damping. In alternate law turn co-ordination is lost so if it's needed one can use rudders to do that. There is embargo on rapid recycling of rudders fro one end to other. During cross wind landing after flare it's normal to take-off the crab by using rudder to align with the runway. But if downwind drift develops then it cannot be corrected with rudder alone. It requires some bank and if it's not enough then a go around is the only answer.

[anson harris]

B2N2

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