Slowing down the aircraft in x wind!!

[Hakeem]

You are arriving on a wet runway with the cross wind from right as you touched down your aircraft is drifting to the left. What do you use??

a) Differential reverse thrust
b) Differential braking
c) Full opposite rudder

I would go for " C " But when I was discussing this my friend came up with a point saying that option " C " is not required right rudder it is full opposite rudder so he said I would go for " B "...

My question is can you guys really use differential braking during the high speed like the seconds after touch down????

Thanks in advance!!!

[pulse1]

isn't there another option?

d Into wind aileron.

[Intruder]

D) Go around.

FLY THE AIRPLANE! Do NOT land with drift on a wet runway!

Full rudder will likely take you off the other side of the runway.

BTW, what does your FCOM/Flight handbook say?

[decurion]

Check out Fig 6 from http://www.nlr-atsi.nl/eCache/ATS/14/919.pdf

[Avenger]

The Boeing FCTM has guidance on this subject.

Differential braking.. No you use Autobrakes

Reduce reverse, differential reverse.. No

Rudder, autobrakes are the best option with reduction in reverse. ..

[Hakeem]

@ Pulse 1

Ailerons into the wind should be right answer But I afraid that option was not there...

@ Intruder

Thats exactly what my friend said But I would seriously think about using differential brakes at that high speed and with out castering nose wheel steering...

@ Decurion

Thanks for that reference...

@ Avenger

Cool that explained every thing

[Microburst2002]

I think that first of all, in such a case you have to reduce reverse thrust to idle.

Thereafter, use everything you have: rudder, diff braking and even nose wheel steering

[low n' slow]

To track the runway in a crosswind, roll into the wind with ailerons and keep the nose from weathervaning by using downwind rudder. Slight forward pressure on the yoke allows the nosewheelsteering to become more effective. I think these corections generally apply to most aircraft.

The aileron input is very important on the little Saab that I fly. Without it it is impossible to maintain the centreline in a noticeable crosswind. Keep flying the plane, the wing doesn't care what the gear is doing...

/LnS

[Lonewolf_50]

low n slow:

There is a limit to that aileron into the wind, "top rudder" technique when landing large transports (from another thread, I recall one of the heavy pilots pointing out that 6 degrees AOB on one of the Boeings 7xx series risks wingtip strike ...).

In this case, what works for a small aircraft isn't quite as helpful when wingspans increase. Other techniques are thus required ...

[A37575]

Edited extract from the 737 FCTM re crosswind landings on a slippery runway.

Assume autobrakes previously selected.
Standard crosswind landing technique. If reverse thrust side component drifts the aircraft to the downwind side of the runway, correct back to the centreline, by reducing the reverse thrust to reverse idle and release the brakes.

This minimizes the reverse thrust side force component without the requirement to go through a full reverser actuation cycle and improve tyre cornering forces for re-alignment with the runway centreline.

Use rudder pedal steering and differential braking as required to prevent over correcting past the runway centreline. When established near the runway centreline, apply maximum braking and symmetrical reverse thrust to stop the aircraft.
............................................................ ...............................

If it sounds real complicated well it is. It needs to be practiced several times in the simulator to become anywhere near safe. First of all, note the FCTM statement "reduce reverse thrust to reverse idle and release the brakes". From full reverse in the 737 to reverse idle of 23 percent N1 takes around 10 seconds of winding down. If you miss the idle detent and go straight through from full reverse to normal forward thrust idle detent, it is likely you will be around 50-60 percent N1 as the reverse levers are fully down. That means significant forward thrust just when you don't need it - especially on a slippery runway.

In fact, snapping the reverse thrust levers from full reverse straight to the forward stops could mean at least 60 percent N1 forward thrust still running down remains by the time the reverser panels have stowed. That can be positively dangerous on a short wet runway. It is often quite difficult to judge exactly the position of the reverse levers that will give you idle reverse. You need to practice that movement in the simulator. And you need to do it quickly - not a slow lowering of the reverse levers.

Now decide exactly how you will release the autobrakes at the same time as you are selecting reverse idle. This can be tricky. You have to do this quickly if you are sliding sideways. Read the FCTM advice step by step. If the autobrakes are armed and immediate braking takes place on touch down, then think about how you are going to quickly disarm the autobrakes. Don't put the speed brake down for obvious reasons even though this is one method of disarming the autobrakes.

Should you switch off the autobrake selector which will give you instant release? Or should you tramp on the manual brakes in the hope of disarming the autobrakes first go? The book says release the brakes not hit them harder to disengage them! How heavy should you squeeze the brake pedals in order to disarm the autobrake sytstem? You cannot afford to experiment with over-riding the autobrakes via manual pressure because it all depends how much pedal pressure you need. Remember you may be still sliding sideways.

It may be that the quickest, efficient and most certain way to disarm the autobrakes, is by simply switching them off. So that leaves you with no brakes at all for a couple of seconds and reverse winding down. Not a good situation to be in on a slippery runway but no choice if you stick to the FCTM advice on the subject.

With some nifty pedal work and now differential manual braking you get the thing straight down the runway albeit the crosswind is a problem. Now you select full reverse again while keeping in mind that from idle reverse of 23 percent N1 to full reverse N1 takes at least 6-8 seconds of winding up.

By now you are applying full manual braking as per the FCTM. If the aircraft starts sliding sideways again then go back to square one and start again.

What pilots need to get into their heads is it is imperative to get rid of the autobrakes if the aircraft starts going sideways under the influence of the sideways component of reverse and weather cocking into wind. This may be hard to accept but there it is in black and white in the Boeing 737 FCTM.

In my experience few simulator instructors set up this slippery runway crosswind scenario for practice. It takes real flying skill and needs to be practiced until perfect. Many new pilots to the 737 have their own handling problems with basic strong crosswinds on a dry runway - let alone the situation described above.

Just remember to brief the other pilot of how you intend to handle things.

[Colin Oskopi]

Dry runway; kick off all of the drift

Wet runway; kick off half the drift

Contaminated runway; kick off none of the drift

On differential braking, the auto brake does it, why can't you? (Why did they give you two brake pedals?)

Use what ever means you have available to control the aircraft.

P.S. I'm Airbus.

[ECAM_Actions]

A critical point not made clear is that by releasing the brakes you can help regain traction and help reduce the slip by allowing the wheels to spin freely. Failure to release the brakes, even with ABS, could reduce traction and make it harder to stay on the runway.

Don't forget to plant that sucker, either. You must break through surface tension or slush if landing on a wet/contaminated runway. A gentle touchdown/greaser is not what you want.

I'd also maybe suggest delaying reverse thrust until you're on satisfactorily. It gives you two options: get the aircraft aligned then stop (the brakes alone are designed to stop the aircraft, reverse thrust just takes some of the strain, so no reverse may greatly aid directional control), and if you haven't pulled reverse, you have the option of going around if you keep heading for the grass.

Reverse is an option, not a requirement. Using it limits your options. Consider also the effect of asymmetric/failed reverser deployment (e.g. downwind engine reverser fails to deploy). It's the last thing you want!!!

[Sammetje]

Why you should reduce reverse??

[safetypee]

Why you should reduce reverse?
See the links in post #16:- http://www.pprune.org/tech-log/455261-reverse-thrust-x-winds.html#post6530636

[Sammetje]

thanks a lot safetypee fig 6 helped a lot!!!

[bubbers44]

I hope the Airbus pilot never lands a tailwheel airplane. You should never land any airplane in a crab. It is hard on the landing gear and if it has a tail wheel you will be spending some money on wingtip repairs after your ground loop. Thousands of hours of instructing xwind landings and retiring in widebody jets with a major airline the sideslip to null out the crosswind always worked for me. I have never landed in a crab ever after 23,000 hrs because it is too hard on the gear landing sideways. Even the DC8 and B747 could be landed this way respecting the max bank at touchdown. Overcontrolling during flare and getting too much of a bank angle could cause a problem so just fly a stable approach to prevent a nacelle scrape.

[PantLoad]

Please show me an authoritative document where it says all this.....

Like...on contaminated runway....land in crab.....OK......good luck,
Striker, we're all counting on you....

Don't mean to be rude....really, I don't, so I'll simply say this,
"Please show me an authoritative document where it says all
this XXXXXXX."


Fly safe,

PantLoad

[stilton]

Our 75/67 flight manual used to recommend NOT taking out the drift before touchdown on a wet or contaminated runway.



The reason given was to reduce downwind drift after touchdown.



This was later revised to recommend taking out all drift.



In a very strong (close to limit) crosswind on a wet or contaminated runway
I still think its more important to get it down in the right place.


You may not be able to take out all the drift prior to touchdown without getting blown too far downwind from the centreline.



You are not going to damage anything touching down crabbed on a wet runway providing your descent rate is not excessive. More important to stay ON the runway.

[scotbill]

Surely phrases like "kick off drift" should not be part of a professional pilot's vocabulary? Try sitting in the last row of an aeroplane 60+ yards long when someone up front applies an agricultural amount of boot at the last moment.
Many students have developed a lasting fear of Xwinds from trying to master the KOD technique so beloved of the RAF and flying clubs.

A controlled sideslip is by far the most polished technique of landing in X winds and the autopilots of aircraft such as the B757/767 are capable of the most impressive demonstrations - landing almost wings level. The principal advantage is that a controlled flare can be made. It must be remembered that the into wind aileron should be held through the flare and landng run. A swept wing can be generating sufficient lift on the upwind side to inhibit autobrake and/or lift dump. The most common fault is to centralise the controls on touchdown.

The 757 in particular demonstrates its dislike of landing with crab on by shaking itself like a wet dog - but the greatest defect of KOD is that, if timing is misjudged, it leaves the machine drifting downwind and the pilot bereft of ideas. A common response is to stuff the nose down - which can result in landing nosewheel first. Now that will very likely damage the aeroplane!
Unfortunately, I gather the Airbus non-conventional control laws have led to a revival of KOD recommendations.
My advice - if you are not a Bus pilot - learn controlled sideslip. It will save you a lot of heartache and works on all types I have flown from the Tiger Moth upwards!

[capt. solipsist]

For the A320:

In case of crosswind various precautions need to be considered:

1) Avoid deflecting the stick into wind. It has practically no efficiency, but has adverse side effects on braking. Indeed, it creates a differential down force on the wheels into the wind side due to the aileron deflection, and it creates a differential drag effect due to spoiler retraction on the out-of-wind side. These differential effects favor the natural "into the wind" turn tendency of the aircraft.

2) The reversers have a destabilizing effect on the airflow around the rudder and thus decrease the efficiency of the rudder. Furthermore, it creates a side force, in case of a remaining crab angle, which increases the lateral skidding tendency of the aircraft. This adverse effect is quite noticeable on contaminated runways with crosswind. In case a lateral control problem occurs in high crosswind landing, consider to set reversers back to idle.

3) In lower speeds, the directional control of the aircraft is more problematic, more specifically on wet and contaminated runways. Differential braking is to be used if necessary. On wet and contaminated runways, the same braking effect may be reached with full or half deflection of the pedals; additionally the anti-skid system releases the brake pressure on both sides very early when the pilot presses on the pedals. Thus if differential braking is to be used, totally release the pedal on the opposite side to the expected turn direction.

[capt. solipsist]

@scotbill:

you surely are gonna get a kick out of this: Airbus prohibits a "controlled sidelip" technique.

however, guess how to perform the "de-crab" maneuver accdg to Airbus?

a rose is a rose... :}

[scotbill]

Thanks for that Cpt S!

Is any Airbus pilot prepared to admit he has found controlled slip works? I'm told the problem is that the sidestick sets an aileron input which is maintained till it is cancelled - but that may be too simplistic?

1) Avoid deflecting the stick into wind. It has practically no efficiency, but has adverse side effects on braking. Indeed, it creates a differential down force on the wheels into the wind side due to the aileron deflection, and it creates a differential drag effect due to spoiler retraction on the out-of-wind side. These differential effects favor the natural "into the wind" turn tendency of the aircraft."

What "into the wind" tendency is that? Taildraggers yes - which is why the pros used controlled slip. But you can crash a tricycle into the ground fully crabbed (as some have suggested on this thread) and the machine automatically tries to straighten up. The important thing on a slippery runway is the aircraft line of inertia - which is why a controlled flare along centre line is preferable to a late adjustment due to (all-too-common) misjudgement of the KOD point.

Surely (sorry - mustn't call you Shirley) the "down force on the wheels into the wind side" is actually what you need to ensure maximum brake/anti-skid efficiency? And the "differential drag ...on the out-of-wind side" would counter any into the wind tendency.

[PantLoad]

You are to be commended for quoting an authoritative document.

Your point #1, however, refers to the aircraft when it is already on the
ground....not the flare and touchdown.

The Flight Crew Training Manual describes the situation....everyone have a
look, please.

Tires have cornering capability and stopping ability....but as Mu
decreases, one cannot expect tires to do both very well. In other,
words, as braking action decreases, you're going to have to accept
one or the other (cornering or braking)....and with less and less
braking action, the trade-off becomes more pronounced.

When wheel are 'crooked' (landing in a crab), you're already
at at disadvantage....cornering and braking.....

This is why the Airbus (and Boeing) procedure is to use
the rudder to align the aircraft with the runway centerline
as you begin the flare. Use some aileron to counteract
any drift downwind.

In 'strong' crosswinds, there may a problem with the above.
There may be geometric limits to 'putting a wing down'. In
that case, some crab at touchdown is to be accepted.
For the Airbus, a maximum of 5 degrees of crab, maximum of
5 degrees of wing down at touchdown. (Reference the FCTM
and the document by Captain Thierry Bourges, Experimental
Test Pilot, Airbus, entitled "Crosswind Landings"....presented
at an OLM FBW conference in 2006.)

The problem with landing in a crab is that, when you grab a
handful of reverse, you will, as Captain Solipsist so correctly
quotes, 'destabilize' the approach. In other words, the reverse
thrust vector is not aligned with the runway....and, it (the thrust
vector) will 'pull' you to the downwind side of the runway. This,
coupled with the fact that, because of the tires not being aligned
(which handicaps their ability to 'corner'), is a prescription for
a runway excursion.

Actually, in this case, Airbus hints that maybe less reverse and
more autobrakes is a better solution.

Landing with more than 5 degrees of crab, for the Airbus, risks
damaging the gear. Further, too much bank risks scraping some
metal. Again, "five and five" is the recommended max. (Ref: ibid)

Good luck, everyone.

[Coldbear]

Hi,

Just to add to Pantlords excelent post. A few quotes from the Airbus FCTM.

FLARE:
"In crosswind conditions, a crabbed-approach should be flown.
During the flare, rudder should be applied as required to align the aircraft with the runway heading. Any tendency to drift downwind should be counteracted by an appropriate input on the sidestick.
In the case of a very strong cross wind, the aircraft may be landed with a
residual drift (maximum 5°) to prevent an excessive bank (maximum 5°).
Consequently, combination of the partial de-crab and wing down techniques may
be required."

ROLL OUT:
"Additionally, the pilot will avoid setting stick into the wind as it increases the weathercock effect. Indeed, it creates a differential down force on the wheels into the wind side and differential drag due to spoiler retraction.
The reversers have a destabilizing effect on the airflow around the rudder and thus decrease the efficiency of the rudder. Furthermore they create a side force, in case of a remaining crab angle, which increases the lateral skidding tendency of the aircraft. This adverse effect is quite noticeable on contaminated runways with crosswind.
In case a lateral control problem occurs in high crosswind landing, the pilot will consider to set reversers back to Idle.
At lower speeds, the directional control of the aircraft is more problematic, more specifically on wet and contaminated runways. Differential braking is to be used if necessary. On wet and contaminated runways, the same braking effect may be reached with full or half deflection of the pedals; additionally the anti skid system releases the brake pressure on both sides very early when the pilot presses on the pedals. Thus if differential braking is to be used, the crew will totally release the pedal on the opposite side to the expected turn direction."

[low n' slow]

An enlightening discussion. Thanks for the posts with explanations about the negatives of rolling into the wind once on ground.

[scotbill]

ROLL OUT:
"Additionally, the pilot will avoid setting stick into the wind as it increases the weathercock effect. Indeed, it creates a differential down force on the wheels into the wind side and differential drag due to spoiler retraction.

I'm sorry guys, this still makes no sense.
I repeat - what "weathercock effect" with tricycle gear?
The only weathercock effect you might get is if the aircraft is already crabbing on a slippery surface - with reverse thrust therefore giving a component across the runway. This is the situation where it might be necessary to cancel reverse.

The danger of not having into-wind aileron is that, for example, it has been shown to delay automatic lift dump on aircraft like the 757. On one swept wing aircraft I remember it was shown that the upwind wing was still giving significant lift at 80 knots - thereby disabling the anti-skid.
Opposite aileron is essential with KOD to avoid any risk of touching wingtip or pod on the downwind side. The controlled slip merely advances that a 100' or so up the glideslope

Could an airbus pilot comment on whether the real reason for their philosophy is a risk of overcontrolling with the sidestick?