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.