Characteristic_speeds.pdf

Characteristic speedsHow to use maneuvering speeds F, S, green dot ?

May 2011Characteritics speeds - How to use maneuvering speeds F, S, green dot ?

Presented by Yves LEMELLE Director of A320/A330/A340 Flight Operational Standards

17th Performance and Operations Conference in Dubai

© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.


Introduction

May I fly below maneuvering speed ?

How much roll maneuverability whenbelow maneuvering speed?

How much Flap retraction for takeoff and Go-Around?

Reduce speed180 kt


Contents


Definitions & Principles1

Maneuvering speeds - Takeoff & Go-Around2

Maneuvering speeds - Approach3

Maneuvering capability4



Definitions - Vls

• Lowest selectable speed• Represents minimum regulatory speeds depending on

flight phase (can be VMCA, VMCL or Vs1g limited)• Provides appropriate margin versus buffet at high

altitude• Provides appropriate bank angle maneuverability

(defined by regulation) in a stabilised turn

Vls



Definitions – F speed

• Takeoff: Minimum speed for Flap retraction• Approach: Target speed for CONF 2 and 3

Also used as maneuvering speed

• Displayed in CONF 2 and 3

F speed



Definitions – S speed

• Takeoff: Minimum speed for slats retraction• Approach: Target speed for CONF1

Also used as maneuvering speed

• Displayed in CONF 1 and 1+F

S speed



Definitions – GREEN DOT speed

• Engine-out operating speed in clean CONF • Best lift to drag ratio speed

GREEN DOT

speed



Principle of characteristics speeds

• Pilot uses Characteristics speeds displayed on PFD:• As limits, to fly between Vls and Vmax (VLE, VFE, VMO, MMO)• As target maneuvering speed (F, S, Green Dot)

• Automatisms use characteristics speeds for:• Predictions, or• Target speeds• Limits


Contents








Maneuvering speeds - Takeoff • To assist pilots• Minimum speed to retract Flaps while aircraft is accelerating.

• At F speed: Select FLAPS 1• For CONF 3 takeoff:

• select FLAPS 1 directly • Speed remains above Vls of CONF 1+F and below VFE

• At S speed: Select FLAPS 0



Maneuvering speeds - Takeoff

Takeoff at heavy weight:

Do not delay FLAPS 0 selection above S speed => prevents possible momentary VFE OVERSPEED warning

In CONF 1+F: S speed could be close to VFE

• If FLAPS 0 selected above Flap autoretractionspeed (210 Kts on this example):• Possible VFE OVERSPEED warning if rapid

aircraft acceleration• No VFE structural limit exceedance



Go Around below MLW

Maneuvering speeds - Go-Around below MLW

• At F select directly FLAPS 1 (as for takeoff)

Retract one step Flaps:• If LDG FLAPS FULL => Go-Around FLAPS 3



Why retract one step flaps only?

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Maneuvering speeds - Go-Around below MLW

• Meets approach climb gradient requirements

Why not retract 2 steps flaps? (Landing CONF3 – Go-Around CONF 1+F)

• Would provide an approach climb performance better than the minimum requirement

• Could result to fly temporarily slightly below VLS CONF 1



Maneuvering speeds – Go-Around in overweight landing

• Conf FULL for landing

• Retract one step Flaps for Go Around

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• If approach climb gradient performance is met:




• Conf FULL for landing

• Retract one step Flaps for Go Around

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• If approach climb gradient performance is met:




17

• If approach climb gradient performance is not met:

LDGCONF 3

FLAPSRetract 2 steps

• Conf 3 for landing to get sufficient climb gradient performance in Go Around

• Retract 2 steps for Go-Around:• To achieve the required climb gradient performance• Meets regulatory requirement of stall speed ratio between

landing and go-around configuration• Could result to slightly fly temporarily

below Vls after CONF 1+F selection.


Contents








Maneuvering speeds - Approach

CONF 1 selectionS

F

F

Vapp

Managed Speed for approach

CONF 2 selection

CONF 3 selection

CONF FULL selection

Green Dot

Speed targetApproach phase activation

Clean CONF

A/THR automatically decelerates the aircraft towardsmaneuvering speed of selected CONF

A/THR does not allow the speed to go below currentmaneuvering speed




• For Flap extension: • IAS must be below VFE next, but may be

above maneuvering speed.

• Recommended (as per FCTM): Next flapconfig at maneuvering speed +10 kts:

• To limit slats/flaps fatigue• For continuous aircraft deceleration




• Flap maneuvering speeds are recommended to fly the aircraft in a given flaps configuration for:

• Performance & fuel efficiency:

• Comfort in cabin:

Holding pattern during initial approach:

Keep Clean CONF and fly Green Dot (best lift/drag ratio)

Green Dot – Clean CONFS - CONF 1F- CONF 2result in reasonable pitch attitudes (typically 5°)




• Flap maneuvering speeds are recommended to fly the aircraft in a given flaps configuration for:

• Comfort in aircraft maneuver:

• Green Dot, S, F are comfortable• Particularly in turbulent conditions,or• For turns at high bank angle

• Flap maneuvering speeds are not limitations:It is safe to fly between VLS and VMAX (VMO, VLE, VFE) : The required aerodynamic margin is properly ensured


Contents








Maneuvering capability

• Roll maneuver as per JAR 25.43 is ensured



Maneuvering capability

• At V2, one engine out:• Stabilized turn at 30° bank before alpha max

• At V2 + 10, all engines operative:• Stabilized turn at 40° before alpha floor

• At Green Dot:• Stabilized turn at 45° bank before alpha prot

• At Vls (final takeoff up to landing) : • Stabilized turn at 40° bank before alpha floor



Can I fly below Maneuvering speeds?

• General rule: Fly approach maneuvers at the maneuveringspeed minimum

• However if ATC speed constraint:• Selected speed• Possible to fly below maneuvering speed down to VLS. It enables

standard maneuvers:• Margin versus Valpha prot is reduced:• Margin could become small in turbulent conditions, or with high

bank angle. If such conditions are anticipated, consider CONF change

• Resume to managed speed when out of ATC constraint

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Maintain 180 kt



Can I fly below Maneuvering speeds?• Example of pilot’s judgement:

Intermediate approach:• ATC speed restriction for significant

time:• If speed slightly lower than Flap

Maneuvering Speed:• May be advisable to keep

current Conf• For fuel efficiency

Maintain 180 kt

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Conclusion

• Maneuvering speeds are comfortable• Allowed to fly below maneuvering speed:Pilot’s judgement according to anticipated maneuvers and turbulence

• Understand the aircraft: Tight turn close to Vls may activateprotections

• Go Around:• Retract one step Flaps• Retract two steps Flaps when required by procedure

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