Manual rudder techniques in crosswind

[Hardy Heinlin]

Good evening,

here's a question for jet pilots, especially 747 pilots :-) But any jet pilot input is appreciated.

(It may be airline specific.)

In manual crosswind landings, to what extent do you use the rudders?

Do you apply the same slip technique the AUTOLAND mode uses in order to reduce the crab angle a  bit? Or should only the autopilot provide this luxury?

I.e., in manual flight, are the rudders taboo until you are down to a height at which you really need all tools to stay on the centerline with wings level?

What if you're hit by an extreme crosswind gust at a relatively safe height, say, 1000 feet AGL? Would you react with the aileron only?

Vice versa, is there any rudder usage limit for manual departure?

(Of course, assume all engines running.)


Thanks!

|-|ardy

[Aidan]

For what it's worth from the Airbus A320 Flight Crew Training manual.

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.

(my writing now) Having said all that the nacelle's will not strike until 16 degrees and most of us rather do things in the following order.

Reduce thrust, flare then kick it straight as the last thing on the list.

if only I could help you more with the 747.

[Hardy Heinlin]

Thanks! On the 747, the bank limit at touch-down, to avoid pod strikes, is 5°.


|-|

[the mad hatter]

well this is quite an interesting question the crab technique is taught as part of your basic stick and rudder skill set ... then with the navy you never have to flare or worry about cross winds... I still apply that same set to the aircraft today its personal judgement

rudders level wings centre line  and kick it bang it down then reduce

[Hardy Heinlin]

Any jet pilot on the forum who applies the slip technique of the autoland system in manual flight? I.e. bank into the crosswind until touchdown, that is, max 5° with the 747. (A320 max 16°?).

With a small aircraft, no problem (I used to do it myself). But with an airliner? For the flight computers it's no problem, obviously. Is it considered too difficult for a human?


|-|

[IefCooreman]

I don't really remember how the 747 ap flies crosswind approaches, on the 777 it does a fantastic demo of wing low technique.

 it boils down to pilot training. The only pilots I've seen doing it on 737 are former RAF pilots. They tend to sideslip from 500ft AGL or something and fly wing-low to the ground. Even on the 737 where the engines are critically low to the ground. You still have 5 degrees which is quite a lot because with 5 degrees of bank, you can cope quite some crosswind. But I've never seen these guys fly 747 or 777. I tend to straighten it up during the flare, lowering the wing only then to prevent drift. collegues on the 747 tend to be more cautious indeed so I guess they prefer to keep wings level.

I've seen people use rudder on approach at say 1000ft. i don't really like it. You have to take into account that the rudder on a jet is much more powerfull than on piston aircraft. it is primarily designed to cope with engine failures. Once you are safe in the air, the working pressure of the rudder is reduced because you don't need it anymore untill on the approach again. And even with this reduced pressure, you can kick a jet on it's back if you want. American airlines knows a nice "left, right, left" can even tear your tailplane of...

In gusty conditions, the FD is your best friend. If you know the method of the four squares, you won't deviate a dot from the localizer. You don't need rudder at all. I only use it very close to the ground, because I don't want my wingtip or engine to experience an earthly encounter . As I said, I've seen people use it because they want to fight the gust. I prefer to 'ride the wind' gently.

On takeoff there is no limit to rudder use. Crosswind takeoff: the amount of rudder kicks you need to stay on centerline during the roll is an indication of the aileron correction you need. If you need rudder, aileron correction is not enough or too much. During rotation you use rudder to keep it straight, then in the air it becomes aileron only and rudder ONLY in case of engine failure.

Cheerz!

[Hardy Heinlin]

Interesting. Thanks for the comments.

In gusty conditions, the FD is your best friend. If you know the method of the four squares, you won't deviate a dot from the localizer.

What's "the method of the four squares"?


Cheers,

|-|ardy

[IefCooreman]

It's a technique, or game, to fly the FD. If you have bar-type fd's and they are perfectly centered, the 2 bars divide the central dot on the pfd in 4 tiny squares. The goal of the game is to keep the 4 squares there all the time (if that makes it any clearer). If one or both of the fd bars deviate too much, you loose two squares, or all of them. Many pilots let the FD bars deviate too much on approach. On takeoff you have to fly 'through' the FD or it will make your flight uncomfortable, but on approach when locked in on an ils, AP and FD are sooooo precise... Even when you deviate from gs or loc, they will gently bring you back on it without too much discomfort this way. Sometimes they will even let you deviate from the ils, I guess there is some wind anticipating software in there but it works like a charm.

 I got it from an instructor who was trained by Boeing on the 747. A game like technique, seems stupid but very effective. your eyes only need to look at 2 places: a dot and a speed tape. Easy.

Anyway, I'm off on holiday now, cheerz

[Autopilot]

Hi there.. First post.. Here goes..

Having flown the 737, 777, A320 and now for the last two years the 744, I can tell you the 400 is very different.

As Hardy has alluded to it doesn't take much to strike an engine pod on landing if your wings arent level.. Much much more so than the other aircraft I've flown.

For that reason the technique we use in my airline is (manual flight) fly the aircraft wings level all the way down the approach. I.e. Crabbed into wind. Then when you get to the flare height, raise the nose slightly, close the thrust levers (around 25R-30R) and then de-crab. That way it's just a second or so until you touchdown and you don't have to compensate for drift by putting a wing down.

People get very !!! nervous if you don't fly wings level near the ground: EFATO, crosswind etc etc...

I won't go into it but there have been a few incidents with engines striking the runway...

[Hardy Heinlin]

Welcome, Autopilot :-)

... close the thrust levers (around 25R-30R) and then de-crab. That way it's just a second or so until you touchdown ...

This brings me to the next question, although not rudder related:

30 .. 20 .......... 10 ........................ touchdown. -- In the old PS1 model the radio altimeter readout was around "0" feet at touchdown (if pitch was ca. 3° to 5°). There was no big time delay after the aural "10" call till touchdown.

In PS1 the RA antennas were located a bit too far from the CG (too close to the nose), therefore the RA was slightly too high above the ground during flare. As we know, at nose gear touchdown the RA reads ca. -8, that's the consequence of adding +8 to the electronics to get a "0" readout at main gear touchdown with the nose pitched up.

Meanwhile I learned that the RA antennas are actually installed closer to the main gear, which is also the case in the PSX model. The sine function of the pitch angle remains the same, though: To keep the -8 feet readout in parking conditions, the 8 must still be subtracted. But at main gear touchdown it now reads -4, not 0.

I guess 0 feet indicates the touchdown of the aft wheel pairs of each tilted 4-wheel group. And -4 feet probably indicates that the groups are finally untilted and that the forward wheel pairs are now on the ground as well -- which also triggers the air/ground relays for the reverser and spoiler stuff.

In other words, if I use the RA -- and the aural calls that are driven by that same RA -- I have to expect the initial touchdown a bit later than in the old PS1. The aural calls 30, 20, 10  actually say 34, 24, 14 ...

There is more time after the 10 call. One can flare a bit later. This also explains some youtube videos were the interval from 20 to 10 appeared rather short to me at first. They looked like hard landings. In fact they didn't touch down at 0. They did at -4, softly.

When you monitor the RA during CAT III training, do you expect the touchdown at 0 feet or rather at -4 feet?


Thanks!

|-|ardy

[Autopilot]

Wow, definetly technical.

I understand what you are trying to do and what you're asking. These questions are perhaps better answered by an engineer or an engineer pilot.


What you are trying to do is def important to get right however to the average line-pilot like myself there are just too many !!! variables on the day. I.e. wind / pressure / temperature / pilot preference of flare technique.

Where there might be such a thing as a standard Boeing landing, most of the time things don't tend to work out that way.

For instance as you said a pilot might have slightly misjudged the flare (not enough) hence the rapid 30-20-10, but then tries to overcompensate it by then flaring slightly faster than normal and might get away with it (i.e. a relatively smooth landing)

To some pilots this might then become their technique. Some pilots judge the flare more by the seat-of-their pants, although again on the 744 (unlike most other aircraft) this is VERY difficult.

In short I would expect the 30-20-10 call to be at the displayed 30R-20R-10R whatever REAL height above ground that might be. Even if the 30R callout came at 34R it would be unlikely anybody would notice, because you just arent looking at the RA indication at that stage. And if you were; it would be changing so fast anyway you wouldn't notice it. (unless you were flying level at 34R or 14R)

In reality though (even on a Cat 3B noDH approach) nobody is really monitoring the RadAlt at these heights (i.e. 30-20-10-0).

I can have a look on my next flight, but I could honestly say that I don't know what it would indicate on touchdown, as from a pilot point of view there are many more important things to think about and monitor at that stage.

RA is just an indication. And like airspeed, most pilots won't be able to fly it to the nearest kt (or 2) because of all the variables in atmospheric conditions...

Hope that helps a little bit

[Hardy Heinlin]

That helps, yes. Thank you!

In the last critical moment of the flare, I understand that the RA may not be a primary part of the pilot's instrument scan. However, I also thought that in some airlines this may be different, especially in those airlines that have the RA inside the ATT indicator (pilot head down a bit more), with the RA display moving with the LOC pointer and rising with the Rising Runway symbol until touchdown. This EFIS configuration is used by UAL, I think.

With such an instrumentation, during a CAT III flare, I assume the PF looks out the window and the PNF monitors the Rising Runway on the PFD (and during rollout the IAS and LOC on the PFD).


Cheers,

|-|ardy

[Autopilot]

You're right.. its there and to be used. However from my pov in my 12 years of flying even in Cat 3 I find it not much use. For me its far easier scanning the LOC 'diamond' and the RadAlt for the various target altitudes* (as PNF).

There are 2 cases we are talking about. One is 'Better than Cat 1' (e.g. CAVOK )weather conditions and obviously the other one 'Less than Cat 1' (e.g. Cat3) conditions.

Lesson one in flying / landing is that it is far easier to fly by looking outside. (apart from maybe judging the flare height in a 744)

That is you have a artificial horizon inside, but the actual horizon outside is much much bigger ;-) and far easier to judge changes in flight path. Likewise with the rising runway symbol. In good weather conditions you'll have the actual runway and its much easier to judge.

Even in Less than Cat 1 conditions it is far more helpful scanning the fd, loc, gs, speed, thrust, wind, than it is to scan the rising runway (all IMHO !!!).

This is all an aside and not much to do with you since the 744 is fitted with a rising runway, so more of an issue with Boeing, than you

* Target altitudes like:

2500R ...... You're getting close to the ground
1000R ...... You need to be stable in the approach config + ldg checklist complete
 500R ....... Ultimate stable gate
 DH    ........ obvious

With such an instrumentation, during a CAT III flare, I assume the PF looks out the window and the PNF monitors the Rising Runway on the PFD (and during rollout the IAS and LOC on the PFD).

Correct, except that before the touchdown (which you will pretty much always feel, no matter how smooth) the NHP will mainly be looking for failures in the autoflight system e.g. Autopilot disconnect, LOC deviation etc

[jonb]

I'd agree with all autopilots comments there. I'm not sure what use that rising runway on the PFD is, personally I never notice it in use.
I scan the RA readout a lot below  say about 200ft on LVOs and then it's heads out the window from about 50ft above RA minima searching for lights.
Also I wouldn't try a wing down method in the 747, it's too easy to strike the outer engines. Combined flare and a kick off of the drift at around 25-30 ft while counteracting the tendency for the upwind wing to rise with a bit of aileron.You've also got to keep flying the wing down to about 60kts to stop it banking in a strong crosswind.
You can also land the thing sideways on a wet runway without decrabbing, but personally I've never had the balls to try that !

Cheers

Jon B