is there a rule of thumb for crosswind landings?

[emerydc8]

Jon, V2 failures would be a training item only, and might be practised depending on airline. The EASA regulations are for a failure after V1 and before V2, I think, and at light weight as you know V1 and Vr will be coincident, which is where the engine is normally failed.
Peter.

Thanks, Peter. I guess we had some sadistic check airmen at Polar.

[ahaka]

Is it normal that with a 20-30 knot crosswind full rudder is needed at times to maintain directional control after touchdown?

[emerydc8]

No. I think it would take more like 30 to 35 knots for full cross-control after touchdown to keep it on the centerline. Maybe more. Maybe Peter can chime in here.
Jon

[IefCooreman]

I don't know of anyone who is good enough to duplicate the sideslip (wing low) method used by the autoland, especially if the conditions are gusty (and they usually are). This technique is a combination of the crab and slip where you land slightly wing low on the upwind gear first. I wouldn't bother practicing this. Go with the de-crab technique.

Seen it done by a retired RAF guy about 10 years ago on the 737 (Jaguar guy... the turbine version). Around 400ft he transitioned from crab to wing-low and my mind went "Dude... really?" But the centerline was dead center and straight up, and that didn't change 'till touchdown...

When he passed away very unexpected, I started to see it as a "respectfull" challenge to try it myself. If there are no gusts it's fun. But if there are gusts your brain needs to be very feminine to coordinate that stuff, while at the same time the image of an engine pod scraping the tarmac haunts you every single feet.

In respectfull British style I will usually yell "Oh sod it!" at 100ft, go quickly back to the "tried & trusted" way of flare-ing, and hope I don't become a youtube posted crosswind landing...

[Hardy Heinlin]

I think it would take more like 30 to 35 knots for full cross-control after touchdown to keep it on the centerline. Maybe more.

When PSX does autolandings, it will set full rudder after touchdown for a second when the crosswind is above 35 knots.


|-|ardy

[Panos Bilios]

Hi
It's great fun to practice crosswind landings with PSX
I use the Brussels situ with 20 and 30 knot wind
It's all about timing with the de crab doing it right I nail
Every landing otherwise I am blown off the centerline

Panos

[cagarini]

I too like to shoot x-wind approaches, but my biggest grip is the visuals :-/

For a start not having a proper PAPI is a bit limitative. Then at some airports like LPMA, where double PAPIs are used and good lateral view is also mandatory, it becomes rather complex...

Maybe one day I'll be able to decently use PSX with a visuals generator - XP12 or MFS ...

[Panos Bilios]

Although I have never used an external scenery system with PSX
I find more than adequate the visual cues provided to complete
A successful landing

Panos     

[Britjet]

Using a completely no-crab procedure won't work in the 747 because of the engine pod clearance, as I think we all appreciate - but it was the approved technique on the 777 when I flew it for BA.

I remember one "limits" landing I did in particular at Heathrow. It is actually quite difficult to keep the nose pointing straight down the centreline on approach without overdoing the crossed-controls which result. The whole thing feels extremely uncomfortable - you can feel the effect of the side-slip.

Also - on the 777 - the amount of control column displacement is considerable - it doesn't leave you with much roll control to play with if you need to keep down a lifting wing - and the physical effort to hold the control in place is quite large.

I didn't like it. Maybe other 777 pilots here could comment..

Peter

[ahaka]

I also enjoy crosswind practice in PSX. So far I can get around 50% of those landings to come out quite nicely. The other 50% are not disastrous but not neat either. Usually what happens is that the nose turns too much downwind after the rudder kick, and I end up having to use opposite rudder into the wind to stay on the runway, resulting in jolting left and right during the braking. It can indeed be quite difficult at times to maintain centerline.

This is most likely due to lack of skill, but I have also been thinking if a better set of rudder pedals with more throw would help prevent overcontrolling. As is discussed in the rudder pedals thread.

In real world, would it even be acceptable if a pilot veers off the centerline as long as the wheels stay out of the edge stripes?

[Hardy Heinlin]

Maybe you decrab too early sometimes? I think it doesn't matter if, during decrabbing, 8 of 16 tires have touched the ground already. (The rear wheel pairs of all 4-wheel bogeys.) If the runway is wet or icy the decrab can start even later.

Here's a nice side drift of a 747 after decrabbing: https://youtu.be/YdVupou9ZZA?t=217

I'm not sure if that happened because of a sudden crosswind increase or because they flared too far.


Regards,

|-|ardy

[IefCooreman]

What was explained to me during initial training: when doing small corrections, the FBW is still "correcting" a lot for you, the control wheel displacement is a request for a certain gentle roll and the FBW will give that roll and "cover" for outside influences. You basically "massage" the control wheel and steer the aircraft on a certain path.

However, from a certain control wheel deflection, the FBW will forget the stabilisation and interpret the deflection as a demand of the pilot: pilot wants to roll, and he wants it now. And the FBW will all of a sudden give you his "full force" and the resulting quick roll. And then you get surprised and you have to correct again and... result: pilot induced oscillation.

Hence, flying wing-low I was scared that the FBW at one point would kick my b...t. Never dared it.

Nice example of FBW giving the pilot a piece of it:

https://www.youtube.com/watch?v=02ddnGzxNZs

The jumping from one main gear to the other is the usual result, you see it many times on the 777. It's not the aircraft, it's the pilot oversteering left/right during the flare.

[Will]

Hallo Ief, thanks for posting, I hadn't seen that video before. Nice wing flex with the gusts.

There are lots of high-quality videos shot in cockpits these days, but in most of those the landings seem fairly benign. (Maybe flight crews choose not to make & release videos of challenging experiences? Or maybe challenging experiences are just that rare?) In any event, it would be interesting to see a landing like this from the cockpit.

[ahaka]

Nice video, Hardy. Looks a bit like one of my landings in PSX.

I have built a habit to start the de-crab when I hear the callout "ten". Perhaps I could try waiting for the speedbrake servo sound? I also think I just need to be more careful with how I ration the rudder. It is easy to overdo it cause the heavy aircraft takes a while to respond and has huge inertia. It feels very rewarding once you get it right though.

[Britjet]

I believe the recommended height to start to remove the crab is 30 feet.
Easy to say - at 30 feet in strong wind and turbulence the aircraft (like all others) has a mind of its own...
Peter

[Panos Bilios]

Thanks for your tips Peter, I was removing the crab at 10 feet RA
I find it much more easier at 30, my crosswind landings are getting much better now!

Panos

[andmiz]

There's 3 methods described by Boeing as applicable. Decrab, no crab and sideslip.  The issues with sideslip and pod clearance are obvious, however interesting to note that autoland in a weak-to-moderate crosswind will utilise sideslip instead of a crab.

The manuals state 'just prior to touchdown' to decrab, and that's generally what I do.  A fair kick to align with the centreline just before touching down, as this allows for better protection against having the crosswind drift you off the centreline.  Decrab too early and you run an increased risk of having to use aileron input to prevent sideways drift off the centreline and increased risk of a pod strike.

Important to remember that you can land with no crab at all, so decrabbing and getting it wrong is worse than just not crabbing at all.

[Hardy Heinlin]

If you say "no crab at all" ... hm ... what exactly do you mean by "crab"? My definition of "crab angle" is this: It's another word for "wind correction angle" (WCA). It's the difference between track and heading. From this point of view, I think it's mathematically impossible to fly at a WCA of zero in crosswind conditions. As we know, the WCA can only be zero when we fly directly into the wind or with the wind, i.e. 100% tailwind or headwind, 0% crosswind.

Or did you mean to say "no decrab at all" instead of "no crab at all"?


)-)ardy

[Jeroen Hoppenbrouwers]

A long time ago we let the then brand-new Lufthansa 747-400ER sim land without decrab and after a terrible sound from below, the thing froze dead and announced "lateral forces exceeded, please insert coin for next game."

Ok that was without iced-over runway  :-)


Hoppie

[cagarini]

If you say "no crab at all" ... hm ... what exactly do you mean by "crab"? My definition of "crab angle" is this: It's another word for "wind correction angle" (WCA). It's the difference between track and heading. From this point of view, I think it's mathematically impossible to fly at a WCA of zero in crosswind conditions. As we know, the WCA can only be zero when we fly directly into the wind or with the wind, i.e. 100% tailwind or headwind, 0% crosswind.

Or did you mean to say "no decrab at all" instead of "no crab at all"?


)-)ardy

Or.. he's referring to the typical fwd slip technique, although the danger of pod strike should probably forbid it's use under stronger x-wind components... This is the one I prefer for most of the gliders. Limit has been landing an AS-K21 with 15 knot effective x-wind :-)  but then, I don't have the pod limitations :-)