Characteristic_speeds.pdf

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Characteristic speeds

How to use maneuvering speeds F, S, green dot ?

Presented by Yves LEMELLE

Director of A320/A330/A340 Flight Operational Standards

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Introduction

May I fly below maneuvering speed ?

How much roll maneuverability when

below maneuvering speed?

How much Flap retraction for takeoff and

Go-Around?

Reduce speed

180 kt

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Definitions & Principles

1 Maneuvering speeds - Takeoff & Go-Around

2 Maneuvering speeds - Approach

3 Maneuvering capability

4

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Definitions & Principles

1 Maneuvering speeds - Takeoff & Go-Around

2 Maneuvering speeds - Approach

3 Maneuvering capability

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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

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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

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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

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Definitions – GREEN DOT speed

• Engine-out operating speed in clean CONF

• Best lift to drag ratio speed

GREEN

DOT

speed

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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

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Definitions & Principles

1 Maneuvering speeds - Takeoff & Go-Around

2 Maneuvering speeds - Approach

3 Maneuvering capability

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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

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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 autoretraction

speed (210 Kts on this example):

• Possible VFE OVERSPEED warning if rapid

aircraft acceleration

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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

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Why retract one step flaps only?

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

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Maneuvering speeds –

Go-Around in overweight

landing

• Conf FULL for landing

• Retract one step Flaps for Go Around

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Maneuvering speeds –

Go-Around in overweight

landing

• Conf FULL for landing

• Retract one step Flaps for Go Around

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Maneuvering speeds –

Go-Around in overweight

landing

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• If approach climb gradient performance is not met:

LDG

CONF 3

FLAPS

Retract 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.

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Definitions & Principles

1 Maneuvering speeds - Takeoff & Go-Around

2 Maneuvering speeds - Approach

3 Maneuvering capability

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Maneuvering speeds -

Approach

CONF 1 selection

S

F

Vapp

Managed Speed for approach

CONF 2 selection

CONF 3 selection

CONF FULL

selection

Green Dot

Speed target

Approach phase activation

Clean CONF

A/THR automatically decelerates the aircraft towards

maneuvering speed of selected CONF

A/THR does not allow the

speed to go below current

maneuvering speed

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Maneuvering speeds - Approach

• For Flap extension:

• IAS must be below VFE next, but may be

above maneuvering speed.

Page 20

• (as per FCTM)

:

Next flap

config at maneuvering speed +10 kts:

• To limit slats/flaps fatigue

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Maneuvering speeds - Approach

• 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 CONF

S - CONF 1

F- CONF 2

result in reasonable pitch attitudes (typically 5°)

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Maneuvering speeds -

Approach

• 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

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Definitions & Principles

1 Maneuvering speeds - Takeoff & Go-Around

2 Maneuvering speeds - Approach

3 Maneuvering capability

4

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Maneuvering capability

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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

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Can I fly below Maneuvering speeds?

• General rule: Fly approach maneuvers at the maneuvering

speed 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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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 activate

protections

• Go Around:

• Retract one step Flaps

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Characteristic_speeds.pdf