Boeing NNC max X-wind

[Barronflyer]

Hi there

I'm wondering if someone can shed some light on the following

The BOEING MANUAL states a max steady crosswind limit. Hence gusts are allowed (the way I read it)

In the non normal section of the QRH however with certain failures the crosswind LIMIT is further limited due to control surface degradation

Can anyone tell me if this reduced limit is a MAXIMUM hence no gusting allowed for?

Many thanks

[FCeng84]

I believe crosswind limits are with respect to the steady crosswind component, not the gust. The steady crosswind dictates the required crab angle and thus the magnitude of the decrab / runway alignment that is needed just before touchdown. The concern with failures is having sufficient control power to perform the decrab plus required maneuvering.

[Intruder]

From our 744/748 FCOM:
Takeoff/Landing Crosswind Guidelines
The crosswind guidelines shown below were derived through flight test data and
engineering analysis. These crosswind guidelines are based on steady wind (no
gust) conditions and include all engines operating and engine inoperative. Gust
effects were evaluated and tend to increase pilot workload without significantly
affecting the recommended guidelines.
Without further annotation, the definition remains -- steady wind only is considered.

[Willit Run]

The 747 is a real beauty to land in a strong crosswind. However, if the runway is at all wet, be very very careful. I landed in LEJ a couple years ago with something around 40 knots direct cross and rolling down the runway, you could feel the plane being pushed sideways across the runway. That was the first time I actually felt out of control.
The side slipping on the runway didn't stop until about 30 knots.

Next time, I'll go hold for 20 mins.

[Qwerti]

The crosswind guidelines shown below were derived through flight test data and
engineering analysis. These crosswind guidelines are based on steady wind (no
gust) conditions and include all engines operating and engine inoperative. Gust
effects were evaluated and tend to increase pilot workload without significantly
affecting the recommended guidelines.


I see exactly the same in the 737 FCTM. In that case, as Intruder mentioned earlier, thats the correct way to interpret Mr Boeing.

Some operators DO include half the Gust in their XWIND component which brings you on the safe side. And strictly speaking.. strong winds usually come with gusts:} Personally, I never had the pleasure of a "steady&strong" crosswind.

What failures and what model are you talking about, if you could be more specific?

[mustangsally]

https://www.youtube.com/watch?v=_z2LtHrn9Jw


De-crabbing is not part of the certification. The above link is a 777 landing with max cross wind. Note there is no effort to de-crab or wing low methods used. Might be hard to sit through, but actually just a nice firm plant.

[Denti]

Most probably just a company restriction, but in our 737NG FCOM the limits are including all gusts. They are hard limits, not demonstrated crosswind capability as well.

[Intruder]

Our company has evolved from hard limits including gusts to "guidelines" of steady state only. They don't tell us why, though...

[RAT 5]

Some opinions please. Many operators have guidance on headwind & crosswind components, including gusts. There are also tailwind limits, either 10 or 15kts. I've asked, searched for guidance on the inclusion of gusts with a tailwind. Total silence and blank faces.
A real scenario: tailwind limit 15kts. (landing on opposite rwy not possible). Actual tailwind 14kts gusting 28kts. Can you legally land? 1 company a/c diverted 2 company a/c landed. Asked for guidance. No reply. Opinions? Rwy was very long, hence the 15kts.

[stilton]

Our guidance on the 757 / 67 is to NOT remove the crab while landing on wet runways.


This will reduce any downwind 'sliding' after touchdown.

[Willit Run]

You have to remove the crab eventually! The fact that you are rolling down the runway with a wet surface and a very strong sideways component,sliding sideways is gonna happen to some extent. Its the ole friction co-efficient........

My advice ; speaking from experience only..... Don't try and "demonstrate" a new limit.

[mustangsally]

I will speak from many years of experience over a wide range of large airframes. Lots of Boeing, 727 through the74, and some AB, 300 series. When touching down on a wet runway the airframe naturally de-crabs. This is set up by the increasing friction, or side load on the wheels and gear. Many companies also require the nose gear to be on the runway prior to entering reverse thrust. (This extra contact and vector will allow the direction of the rolling airframe to remain closer to runway alignment than with only the main gear in contact with the surface.) If you watch the Boeing video referenced earlier, you will see the airframe de-crab as it continues the roll out. Now some rudder input may be applied and with some aircraft includes the nose wheel steering to some degree. The mass the of airframe wants to continue down the centerline and not at the crab angle.


Just prior to touchdown the crab angle keep the airframe s lined with the runway, after touch down the crab angle is reduced to zero very shortly after touch down by the friction and vector mass of the airframe.


Not sure if this helps.

[stilton]

What he said :ok:

[RAT 5]

And then immediately the cross wind component will attempt to steer the a/c back towards the crab angle; if you do nothing. The trauma in the tyres is not small and needs some help.

[stilton]

Er, why would you 'do nothing ? '


Those two pedals in front of your feet will do a fine job of heading you in the right direction, before and after touchdown.

[RAT 5]

Just prior to touchdown the crab angle keeps the airframe lined with the runway, after touch down the crab angle is reduced to zero very shortly after touch down by the friction and vector mass of the airframe.


Because this statement might lead some not so well trained mumpties into believing they did not need to be so immediately aggressive with those 2 pedals to align the a/c with the rwy centreline; it will happen automatically all by itself. Therefore I thought it prudent to remind others of what you & I know to be the truth.

[stilton]

I understand and agree with your point.


I believe it is a good recommendation and have followed it myself in very strong crosswinds on wet or contaminated runways, works well.

[con-pilot]

It seems to me that there are pilots out there that don't realize that what is important is where the main gear is in relation to the runway center line rather than the cockpit/nose gear in strong cross winds.

You can see this in a lot of the videos showing strong wind landings. The main gear is somewhere between the center line and the edge of the runway while the cockpit/nose gear is perfectly lined up with the center line.