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B737 crosswind landing
Hello, I'm B737 FO and I'd like to ask about the relationship among LOC, main landing gear and FD for heavy crosswind landing.
- According to B737 TM, "whenever a crab is maintained during a crosswind approach, offset the flight deck on the upwind side of centerline so that the main gear touches down in the center of the runway." - LOC antenna is located at radom. Q.When crab is maintained during heavy crosswind(ex 30 kts) If the LOC pointer and FDs are on center, does it mean A/C nose(radom) is on extended RWY centerline and main landing gear on downwind side? If yes, how can I maintain main landing gear on extended RWY centerline during crab approach? Should I be on upwind side while LOC pointer and FD on downwind side? Best regards, |
You're to look outside at that stage... yes the LOC bar won't be centered any more.
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Seems like it would be a real but minimal effect.
A little trigonometry says that for a 737-8, with the main gear about 20 meters behind the nose, and a crab angle of 5°, the nose would be offset about 1.7 meters upwind of the runway centerline when the main gear are centered either side of the runway centerline. For a 3000-meter runway, with a TD zone 500 meters down the runway (2500-meter LOC range), the nose being 1.7 meters left or right of centerline would show a 0.04° needle deflection downwind at the touchdown zone. And since full-scale deflection of the LOC needle for an ILS is 2.5°, that would mean the LOC needle deflection would be about 1.6% of the full deflection. Probably less than the width of the needle itself! Longer runway or shorter airframe (731/2/3/4/7) or smaller crab angle - the LOC needle deflection will be even less. Over the threshold it will also be even less. Longer airframe or shorter runway or larger crab angle would result in more visible deflection. Someone can check my math - sines and cosines were never my favorite subject. |
Originally Posted by safelife
(Post 10380262)
You're to look outside at that stage... yes the LOC bar won't be centered any more.
+1 use the Window.... |
pattern_is_full
I won't double check your math, but to at first glance, I'm sure your conclusion is right, and the effect is negligible. |
Too much thinking and not enough hands on! You definitely shouldn't worry about this, just look out the window and fly the plane! You can de-crab a 737-800w up to about 20kts of crosswind, but after that there's not enough aileron authority to keep the wings level so you crab the rest.
Even if the mains are not on the centre line, they soon will be as they're pointing the right way to make their way onto it! Just remember, the autobrake will effectively de-crab for you, just keep it going down the middle with the rudder and keep the into-wind aileron fully in at least until you get control taken off you by the skipper. the untidiness is his/her problem after that. |
This sounds like my time at KAL. After a captain would smash the plane on the ground, he would have me print up a landing report.
"Ah. I flared 3.2 degrees. I should have flared 3.3 degrees!" No, you should have been looking out the window. |
The big rudder on the 737 makes it capable of crosswind landings way above the demonstrated limits. I don’t look at the localizer when I fly close to the ground, but I keep the nose upwind of the centreline. I don’t fly in a wing down/de crabbed state ever, just kick the nose straight and drop the wing just before touch down. It works but takes a bit of coordination to get it right. With this procedure I have done crosswind landings with 50kts crosswind in the simulator. |
Originally Posted by ManaAdaSystem
(Post 10381675)
The big rudder on the 737 makes it capable of crosswind landings way above the demonstrated limits. I don’t look at the localizer when I fly close to the ground, but I keep the nose upwind of the centreline. I don’t fly in a wing down/de crabbed state ever, just kick the nose straight and drop the wing just before touch down. It works but takes a bit of coordination to get it right. With this procedure I have done crosswind landings with 50kts crosswind in the simulator. |
What on earth are you talking about?
That's the exact way I've landed every 737 in a crosswind for the last decade. I'm not Red 1. |
Originally Posted by Chesty Morgan
(Post 10381975)
What on earth are you talking about?
That's the exact way I've landed every 737 in a crosswind for the last decade. I'm not Red 1. No, I don’t do 50 kts xwind landings in RL but it is nice to know it’s within the aircraft capability. After all, the tables are just demonstrated limits. |
Originally Posted by ManaAdaSystem
(Post 10381675)
The big rudder on the 737 makes it capable of crosswind landings way above the demonstrated limits. I don’t look at the localizer when I fly close to the ground, but I keep the nose upwind of the centreline. I don’t fly in a wing down/de crabbed state ever, just kick the nose straight and drop the wing just before touch down. It works but takes a bit of coordination to get it right. With this procedure I have done crosswind landings with 50kts crosswind in the simulator. I hope this is just your vernacular and you don’t really ‘kick’ the nose straight Drift should be pushed off smoothly |
Originally Posted by stilton
(Post 10382462)
I hope this is just your vernacular and you don’t really ‘kick’ the nose straight Drift should be pushed off smoothly For a landing in 50 kts xwind I don’t just press the rudder to get the nose where I want it to be, there is an element of inertia involved. A firmer application of rudder than in a 20 kts xwind. I had the pleasure of landing in 50 kts just a few days ago. Xwind was 30 ish. Again, a more firm use of rudder to to put the nose in the right direction. I like xwind landings. That is because I’m confident in what the aircraft can do. It doesn’t mean I don’t stuff up my xwind landings every now and then, but it doesn’t happen very often. |
I'm with Chesty and ManaAda here.
On the 737 (200 to 800 variants). Crab until shortly before touchdown and then squeeze the drift off applying aileron to keep the wings level and erring (if that is the right word) into lowering the into wind wing a little. Worked well in very strong crosswinds with plenty of rudder and aileron left. That was how I was taught and it seems to work for me. Ditto the 757. The 777 was a somewhat different matter as we were taught the wing down method but also that crab was acceptable. Aiming to keep the main gear on the centreline was required. Never did any limiting crosswind landings as at that time I was an F/O. The A320: I once had difficulty in keeping the into wind level on a strong crosswind despite full into wind sidestick (I was reasonably new to type). Talking to some A320 old hands who told me that the drift needed to be removed early in order for 'the system' to catch up. Not sure about the truth in that. The Bus always held some 'mystery' for me but many others loved it. The final approach and landing, whether crosswind or not, and regardless of type, should always be carried out visually. Regards Exeng |
ManaAdaSystem, re # 8, 11, 13 When expressing alternative views it would help if the basis for these were provided. Whilst the size of a control surface could be interpreted as providing greater theoretical crosswind capability, this might not consider if control power can be achieved, or any adverse consequences when attempting to use it. The control response or aircraft motion could be insufficient for the conditions; similarly piloting finesse. Thus the well considered advice to smoothly control the aircraft. The need to ‘kick’ the rudder could be an indication that you are near your crosswind limit; a lack of experience in the conditions, control coordination, or poor feedback - lacking a good feel for the aircraft. Feel is particularly important in judging sideways motion, lateral movement vice sway of normal flight, seat of the pants accelerations - poorly represented (if at all) in simulation. The consequences of large and/or fast yaw inputs in the roll axis requires similar consideration; and beware control reversals or cross control. The aircraft is physically limited, wind tip or pod scrape; both require significant margin to ensure an adequate level of safety. In addition, even if an aircraft can be aligned with the runway for a landing, control is still required on the ground, perhaps a greater need than that required in the air. A hazard of self reference definitions - your ‘max demonstrated’, is that any difference with the agreed industry definition increases risk in operation, reducing safety margins, and adds confusion to the complexities of operation. Furthermore, there may be a greater hazard if an unwary pilot believes these erroneous statements. In a professional forum individuals must consider their responsibilities in what is said; this is best defended with well considered opinion without assumption. For general info: https://www.dropbox.com/s/zq6lxugvoc...ation.pdf?dl=0 (If no App, use website option) |
Say whaaat??
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I think that was what I was saying but slightly more complicated. Yes ManaAdaSystem, I was talking about more of a steady state control ability. The 737-800 can't hold more than about 20kts without wing drop from the adverse yaw, despite full aileron, plus the increased drag really costs you speed and lift.
So yes, I concure, a last second swing round onto centreline can be achieved, but I've seen a lot of these on Youtube, as many where it goes horribly wrong, with overcontrol, wing rocking and other effects as the lucky ones that don't. If you can't hold it steady, then it's what it is. I can smoothy bring it into wind in the flare and hit the aileron stops shortly after 20kts. so over that I accept crab. The aircraft doesn't seem to mind at all. I've always tried to de-crab earlier than some. My bad perhaps. Too late now to chance, I'm closer to retirement than I was....but not close enough. |
June737, #1, Don’t get too concerned about the theory of electronic guidance. The runway is always the primary reference for landing. Crosswind operations are more art than science, although science provides the boundary conditions. Getting a feel for the situation is important, as is being in the loop. These aspects are subjective, something which you have to learn with experience, looking - following through, and practice as allowed; knowing where the aircraft (cg) is, and direction and speed of movement. Re #15 link: has anyone experienced the downwind turning effect during take off? Would this particular mechanism have an opposite effect when using reverse thrust? Is this a concern during takeoff in 737s with the larger engines - intake / fan influence? |
"turning"?? How about "yawing"? Although I suppose it is Airbus/Boeing...
I was surprised they said the effect was "dramatic" and may be limiting. Looking forward to reading comments from the "underslung" people... As for "Max Demonstrated", in my view this is a major copout. An aeroplane must have a limiting crosswind based on the technique used to get it on the ground eg forward slip, the bank angle will be limiting. For the manufacturers to state only the max demonstrated crosswind and not call it a limit (which we all interpret it as) is pretty weak, I reckon. |
Bloggs, in the air an aircraft yaws; on the ground it turns relative to a ground reference - wheels. Being either in the air or on the ground, an aircraft can translate laterally due to wind side force, this is ‘very relative’ to the edge of runway. ;) Certification requirements specify the conditions when the crosswind is to be published as a limit; this is rarely used. Certification is not an absolute science, more probability; in addition we might be surprised by the influence that the operating industry has had on the ‘need’ for max demonstrated. Defining personal limits is a very good safety policy, but not to forget that changes should only be considered after evaluation of landings experienced and not that just before landing. :ok: |
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