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B737 x-wind take-off

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B737 x-wind take-off

Old 30th Dec 2008, 22:07
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B737 x-wind take-off

After reading the Denver thread I did a search for more xwind takeoff info on the 737. The other threads are closed so I thought it couldn't hurt to start another. This is a quote from another thread;

Firstly, about 10 degrees of control wheel movement is required to cause spoiler deployment. This is a very small control wheel input, yet I found this was ample to maintain directional control with a 34 knot crosswind (maximum for my model B737).

There was only 2 degrees of bank on the takeoff roll, yet almost full control wheel input (and full spoiler deflection) was required to level the wings. My opinion is that large doses of aileron/spoiler are not required to maintain directional control.
When I did my type rating we were taught that only 10 degrees control wheel input into wind should be used for a max xwind take-off to prevent spoiler deflection. The rest of the directional control needed, should be achieved by rudder. They also said that the control wheel input will need to be increased through the rotation to keep the wings level and that a rough guide to how much deflection is approx twice the xwind. For example if there is a 20kt xwind, then during the rotation the control wheel will need to be progressively moved through to about 40 degrees deflection.
I have found that this works quite well in real life.
In observing others take off in xwinds I sometimes think that they use too much of the ten degrees allowable aileron and as a result end up with very large rudder inputs to keep tracking straight down the strip. I don't consider myself an expert in this area by any means and would appreciate others opinions (if you are 737 rated).
Cheers, Framer.
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Old 30th Dec 2008, 22:22
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Originally Posted by framer
When I did my type rating we were taught that only 10 degrees control wheel input into wind should be used for a max xwind take-off to prevent spoiler deflection. The rest of the directional control needed, should be achieved by rudder. They also said that the control wheel input will need to be increased through the rotation to keep the wings level and that a rough guide to how much deflection is approx twice the xwind. For example if there is a 20kt xwind, then during the rotation the control wheel will need to be progressively moved through to about 40 degrees deflection.
I have found that this works quite well in real life.
As a former B-737 guy, the only thing I would have added is that as the rotation continues, the aileron input is adjusted to maintain wings level and as the nose gear leaves the runway surface, adjust rudder input to keep the ball centered. Otherwise, I quite agree with all of the above – particularly, the last sentence!
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Old 31st Dec 2008, 01:10
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Is it possible to see on the hydraulic pressure gauge the needle quiver when the spoiler rises? I just had a thought then that this may be the case and prior to lining up I could look at that to get a feel for where the max deflection is.
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Old 31st Dec 2008, 09:54
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In a previous life flying the 737, a tailstrike happened in the company during crosswind conditions.

One of the findings in the investigation was that, due to excessive control wheel displacement (obviously to counteract the effects of x-wind) spoiler deployment occured. This, in addition to the use of flaps 1 which of course also reduces tail clearance, probably was an attributary factor in the scraping the back end (i.e. loss of lift and thus delaying lift off)...

Just my 2 cents worth. TS737

Last edited by TopSwiss 737; 31st Dec 2008 at 09:55. Reason: typo
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Old 1st Jan 2009, 06:06
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Rainbow, I respect your opinion and most certainly your experience butI have never heard any of my training captains or line captains say that the spoiler activation doesn't matter.
Page 3.13 of the FCTM says "Use of excessive control wheel may cause spoilers to rise which has the effect of reducing tail clearance"

I wonder if having more aileron in than is required for the conditions results in more weight on the upwind wheels, which in turn causes a slight pull in that direction, which results in more rudder being required to track the centerline. Does that sound feasible?
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Old 1st Jan 2009, 07:32
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There seem to be so many different opinions as to how much aileron to apply during a crosswind take off on the B737! I go for more rather than less so tend to agree with Rainboe.

But when it comes to a potential tailstrike no mention ever seems to be made of rotation rate. I believe that Boeing recommend 2 to 3 degrees per second. If we take the average of 2.5 degrees per second this means it should take 6 seconds to reach 15 degrees. Quite often I see quite rates of rotation which appear to exceed the Boeing recommendation by a fair amount.

One tip I got was the 10/10 rule - don't exceed 10 degrees pitch up below 10 ft radio height - easy to remember and might keep you out of trouble.

Fly Safe in 2009!
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Old 1st Jan 2009, 11:04
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Spoiler drag on roll is negligible. The darn things don't have much effect below 250kts even, below 140 kts hardly any effect at all
Friend of mine was F/O during a take off in a 737-400 with 25 knot crosswind from the right. The captain pre-set almost full wheel travel right from brakes release. This was his personal choice not a company requirement. The aircraft was runway length limited on this take off. As the story was told to me by the F/O a few days later, around 120 knots the acceleration slowed markedly and at VR the aircraft was extremely close to the threshold.

He described the decelleration as like a car going through a deep puddle and momentarily slowing except this was a 737 that kept going and the V1 was clearly invalid under these circumstances. During simulator training we demonstrate the effects of spoiler extension without reverse actuation or RTO braking during a high speed rejected take off. In the simulator at least there is a definate sense of immediate decelleration and after initial engine spool down the decelleration green arrow is seen on the PFD. As the speed slows below 80-90 knots the green arrow shortens. This suggests that the spoilers when extended at high speed during take off do definately add significant drag for a short period.

This further suggests that excessive control wheel deflection to counter a crosswind in the 737 during the take off run could invalidate V1.
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Old 1st Jan 2009, 11:39
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OK.....let's throw some more wood on the fire.

The way I'VE always done it from day one in a Piper Super Cruiser through many other bug smashers, light to medium twins, Connies, DC-6/7, B-737 (200 & 300), and DC-8s is: Up to max aileron, depending on the amount of x-wind during the initial phase of the take-off roll. As speed increases and the aircraft becomes more "flyable", start relaxing the amount of input. Natural. Of course all this time you're using rudder as well. It IS a coordinated maneauver. The aircraft should lift off tracking right down the centerline, but significantly crabbed into the wind depending on the amount of x-wind, naturally. Don't worry about the darned spoilers. As you start to relax on the wheel with speed increasing, the spoiler deflection will be decreasing.

Simple maneauver.

Next.....
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Old 1st Jan 2009, 12:09
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Those of you reading this who might be fairly new to flying might believe that all that is written by those of us with 'over 20.000 hours' might contain 'good' information. Sadly, this is not the case in this instance, as is so often the case amongst certain posters!.

All the information relating to crosswind take offs from Boeing is contained in this memo.

Read and learn how it should be done!

Memo. Cross-wind Take-off Techniques.

In cross wind conditions it is not uncommon to see large control wheel displacements (and excessive forward pressure) during the takeoff roll in an attempt to improve directional control.

This is not the correct handling technique and greatly increases the
possibility of a tailstrike. The FCTM (3.14 and 3.15) is very clear in this area. The greatest threat to a take-off in strong and gusty crosswind conditions is in fact tailstrike and not directional control.

Guidance material on the prevention of tailstrikes is provided in a number of our approved manuals which are summarised below:

Boeing FCTM: Directional Control
“....Smooth rudder control inputs combined with small control wheel inputs result in a normal takeoff with no overcontrolling. Large control wheel inputs can have an adverse effect on directional control near V1(MCG) due to the additional drag of the extended spoilers.”

Limit of control deflection without spoiler activation 1.5 units

Boeing FCTM: Rotation and Takeoff

“Begin the takeoff roll with the control wheel approximately centered. Throughout the takeoff roll, gradually increase control wheel displacement into the wind only enough to maintain approximately wings level.

Note: Excessive control wheel displacement during rotation and lift-off increases spoiler deployment. As spoiler deployment increases, drag increases and lift is reduced which results in reduced tail clearance, a longer takeoff roll, and slower airplane acceleration.

At lift off, the airplane is in a sideslip with crossed controls. A slow, smooth recovery from this sideslip is accomplished by slowly neutralising the control wheel and rudder pedals after takeoff”

Boeing FCTM: Gusty Wind and Strong Crosswind Conditions.

ALL of this section of the FCTM is crucial to understanding how to avoid a Tailstrike in these conditions but the following is particularly relevant to this memo: -

To increase tail clearance during strong crosswind conditions, consider using a higher VR if takeoff performance permits. Avoid rotation during a gust. If a gust is experienced near VR, as indicated by stagnant airspeed or rapid airspeed acceleration, momentarily delay rotation.

“......Do not rotate early or use a higher than normal rotation rate in an attempt to clear the ground and reduce the gust effect because this reduces tail clearance margins. Limit control wheel input to that required to keep the wings level.
Use of excessive control wheel increases spoiler deployment which has the effect of reducing tail clearance. All of
these factors provide maximum energy to accelerate through gusts while maintaining tail clearance margins at lift-off.”

Boeing FCOM Volume 2
Page 9.20.5, Flight Spoilers, states: -

“The flight spoilers rise on the wing with up aileron and remain faired on the wing with down aileron. When the control wheel is displaced more than approximately 10 degrees, spoiler deflection is initiated.”
10 degrees approximates 1.5 units of Aileron Trim.
Operations Manual Part A
Existing procedures designed to reduce the risk of Tailstrike are: -
Ops A 8.0.10 Co-pilot Flying
When flying with inexperienced co-pilots or a co-pilot newly converted onto type, the Commander shall perform the take-off or landing himself when the following conditions are experienced:
1. Crosswinds more than 2/3rds of limiting value.
Ops A 8.3.0.1.5 – Take - Off Flaps
Flap 5 is the normal departure flap setting; flaps other than Flap 5 shall be used when operationally necessary. If crosswind component is in excess of 10kt fixed derate is permitted, however assumed temperature thrust reduction is not permitted.
All Flap 1 departures shall be flown by the Captain as PF.
Boeing FCTM: Gusty Wind and Strong Crosswind Conditions
The FCTM Gusty Wind and Strong Crosswind Conditions section gives guidance as to how to comply with Boeing’s recommendation that rotation be delayed in these conditions. Specifically: -
“To increase tail clearance during strong crosswind conditions, consider using a higher VR if takeoff performance permits. This can be done by:
• Increase VR speed to the performance limited gross weight rotation speed. Do not exceed VR gross weight + 20kts.
• Set V speeds for the actual gross weight. Rotate at the adjusted (higher) rotation speed. This increased rotation speed results in an increased stall margin, and meets takeoff performance”
In practice, this means that there is no change to procedure and PM will call VR at the set speed but PF may delay rotation to the gross weight VR.

Summary

• Smooth rudder control inputs combined with small control wheel inputs result in a normal takeoff with no overcontrolling.
• Any control-wheel deflection more than 10 degrees (approximately 1.5 units of Aileron Trim) will activate the spoilers.
• Spoiler activation reduces aircraft energy which requires a higher attitude to generate the lift required for takeoff. This increases the risk of a Tailstrike.
• Do not rotate early or use a higher than normal rotation rate because this reducestail clearance margin.
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Old 1st Jan 2009, 12:26
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Rainboe,

Just an aside to your comments regarding the minimal effects of spoilers at low speeds, I remember from my B707 days that there was a performance weight penalty to be applied when taking off in crosswinds that exceeded 15kts component to allow for the spolier drag although I can`t remember (senior moment here) if there was an aileron `dead band` or not but the handling advice was "aileron angle on the yoke equal to the crosswind component". B737 and B747 both had similar advice. It is only the AIRBUS that mention restricting the aileron to a value below spolier deployment value.

PS in 41 years flying - 6 years on the VC9. Now that really was a horribly handling aeroplane!
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Old 1st Jan 2009, 15:16
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Rainboe -

"The way I see it, ANY aileron has no effect up to about 80 kts in a big jet, so why not just hold the estimated amount on steady from the start, and leave it there and not worry about it again?"

You'll note that I said UP TO max deflection depending on x-wind. Kinda the same as your "estimated" the way I see it.
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Old 1st Jan 2009, 15:39
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Rubik 101 Hear hear. Why do people try and reinvent the wheel?

The manuals are the authoritative source of information on how to fly your aircraft. If a problem arises and you have deviated from the manuals because of wives tales and "this is the way I have always done it" your tail is on the line! Not only from the company but god forbid if you were ever then in court trying to defend yourself.

I am not a test pilot and I hope never to be, thats why boeing airbus etc employ people to do these things, Im sure they have tried everything and found the best way to handle the aircraft.
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Old 1st Jan 2009, 16:21
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Post #5
A search would have brought up a cascade of information here about all this. But can you say how much drag you think a cracked spoiler gives you up to 140kts when you get airborne? Do you think 10 degrees of aileron is really enought to prevent wing lift at higher take-off roll speeds?
I dunno Rainboe, I am not a performance engineer.
Was just trying to put some info from an extensive incident report into this thread...

Boeing procedures seem to support this I guess...
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Old 1st Jan 2009, 16:21
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Well, there's the right way, the wrong way, the company way, the manufacturer's way, the test pilot's way, and the Captain's way. The Captain is always right, right?!

Anyway, between myself, Rainboe, and numerous other Captains on here, we probably have over a million hours of experience compared to a few hundred hours that "test pilots" have.

Boeing said the tail of their 737s could not ice. That was an outright dumb lie.
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Old 1st Jan 2009, 16:28
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So we should just disregard what is written in the manuals and thus becomes a legally binding way to operate the aircraft because you are the oracle?

Tell me which airline you fly for where blatant disregard of the FCTM, Flight manual and SOPS is allowed!

You must be a joy to work with in the cockpit with that god like complex you have. I pity the Fo's that fly for you, they must be constantly in awe as you teach them everything and show them that boeing are wrong!

PS I'm sure the test pilots have more time in interesting situations with the aircraft on the limits of the envelope than the millions of hours that the likes of you and Rainboe etc have. I would trust their judgement a hell of a lot more than your "wives tales."

PPS No the Captain isn't always right.

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Old 1st Jan 2009, 16:52
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In the dim and distant past, I recall an incident where a well known carrier had a 747 classic depart from NRT to LGW, fully laden, and had a hydraulic fault that caused some of the spoilers deployed during TO. This wasn't picked up on the SPI but was noticed by the crew once airborne due to the 'vibration' and sluggish climb. The fault was rectified by isolating the hydraulics to the associated spoilers on the overhead panel, you know the guarded switches we never touch! and the flight continued to destination without further ado. Says a lot for Boeing - it will fly!!
My point is, will a small amount of spoiler deflection really make much of a difference? Just my opinion!
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Old 1st Jan 2009, 16:56
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PS Anyone been to 'The Truck' recently, how I miss that place (NOT!!)
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Old 1st Jan 2009, 17:16
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Rhodes13 -
"So we should just disregard what is written in the manuals and thus becomes a legally binding way to operate the aircraft because you are the oracle?

Tell me which airline you fly for where blatant disregard of the FCTM, Flight manual and SOPS is allowed!"



Come now.....you can certainly read between the lines. It was a take off on "the right way, the wrong way, and the Army way". However, there IS some truth in there if you've spent enough time in airplanes, as many of us have, and seen some of the things that "can't go wrong" that DO go against what you've read or heard. Only experience tells you what can and does happen out in the real world.

BTW.....I'm retired from the Friendly Skies.
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Old 1st Jan 2009, 18:16
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This thread highlights the perils of pprune.I rarely post here for the ritual flaming that accompanies attempting to bring the real world to the party versus 'top tips'and 'pet theories' which abound around here.I am a 737 TRE with a uk leisure airline and previously with the orange brigade.My advice,for what it's worth is that you must follow the FCTM guidelines in conjunction with your company sop's.I will not reiterate that advice-please go read it- but suffice to say that crosswind take off technique is precisely and accurately prescribed and has been contradicted in these posts.Boeing test pilots do know what they are doing and ignoring FCTM guidance to follow pet theories (published on pprune)is perilous and inadvisable.

Happy landings in 2009.
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Old 1st Jan 2009, 18:37
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Test Pilot

"Anyway, between myself, Rainboe, and numerous other Captains on here, we probably have over a million hours of experience compared to a few hundred hours that "test pilots" have."
This may have been a tounge-in-cheek comment, but there have been incidents where airline pilots have done experimental flying with a full load of passengers with bad results. When you deviate from the Flight Manual you are a test pilot without a test plan.

It may not be widely known, but the first 737-100 in the Boeing test program was fitted with bail-out provisions. The Fwd baggage door was hinged on the leading edge and had a hydraulic actuator that could push it open against the airstream. A section of floor panel was removed above it and a grab handle was installed above the hole so that crew members could hang from the handle so that gravity would align them with the open floor and cargo door, g forces permitting. It was never used, but there were a couple of anomalies.

The 737 leading edge devices did not have locks on them initialy because wind tunnel data showed that aero forces would keep them tight against the wing in flight. Boeing has thousands of engineers with every applicable specialty that test and analyze every possibility prior to test flights. During one of the high speed tests the leading edge devices popped out and were badly damaged. The crew regained control despite the resulting asymetric leading edge, and managed a flaps up landing at BFI.

Another anomally was that the original TR's actually caused the 737 to speed up when they were applied. Both TR doors deflected thrust under the wing which created lift that reduced braking effectiveness greater than the reverse thrust forces. The fix was to clock them so that one TR door deflects thrust above the wing.

One in service "test flight" that went badly was a 727 flown about 35 years ago by a fellow named Hoot Gibson. Hoot decided that he could deploy a litte flaps at cruise to achieve a higher altitude. The 27's did have locks on the leading edge devices, but guess what? Hoot just unlocked them! The result was much the same as the 37 real test flight. Hoot took a 30,000 foot spiral dive. Initial press reports extolled his hero flying skills, but when the facts were known he was unemployed.

There is good reson to do it by the book.
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