Control your speed… during climb

Source: Airbus Safety First URL: https://safetyfirst.airbus.com/control-your-speed-during-climb/ Published: 2015-07-29 Magazine Issue: 2015-07 Category: Flight Ops, climb, energy, flaps, green dot, mmo, overspeed, slats, speed, vfe, vmo, weight, zfw PDF: Original PDF

---

006 Safety First #20 | July 2015 PROCEDURES

Control your speed… during climb

Second of a series of articles on the theme of speed control during a fl ight, which started in issue #18 of this magazine, we have just taken off and are now entering the climb phase. The main objective is to retract the slats / fl aps at an adequate speed, while sustaining enough lift to accelerate and climb.

LORRAINE DE BAUDUS

Flight Operations Standards and Safety management

PHILIPPE CASTAIGNS

Experimental Test Pilot

After take-off, the aircraft continues in the climb phase and flies away from the busy airspace. The objective for the crew is to accelerate to the en-route climb speed and at the same time, manage various aircraft configuration changes, usually consisting of gears, slats and flaps retraction, and a change from take-off power to climb power.

This article aims at shedding some light on the way the different maneuvering and limit speeds that are of use during climb are defined and determined, and how they can be implemented in daily operations.

MANAGING YOUR CLIMB: UNDERSTANDING SPEEDS

A climb is generally flown at an airspeed that is often initially limited by Air Traffic Control (ATC) instructions. To safely manage the climb phase within these restrictions, some characteristic speeds are useful tools, and they require a close monitoring. What speeds exactly should be monitored? What do these speeds mean and what happens if they are exceeded?

For every flight, characteristic speeds are computed automatically by the aircraft Auto Flight Systems (Flight Management System (FMS), Flight Guidance (FG) and Flight Envelope (FE)) and effectively displayed on the PFD airspeed scale. They are extremely useful as maneuvering speeds and limit speeds to safely guide the pilots configuration change decisions through the climb phase.

Our objective is to highlight the design and operational considerations underlying all recommendations Airbus has issued to flight crews regarding the monitoring of these speeds during climb.

Amongst other parameters, the maneuvering speeds Flaps (F), Slats (S) and Green Dot (GD) are a function of the Zero Fuel Weight (ZFW) inserted by the crew at FMS initialization. Therefore, any erroneous entry will impair these speeds.

F, S and Green Dot speeds frame the aircraft climb performance limits.

Maneuvering speeds

In nominal conditions (all engines operative), the climb phase poses some challenges to the crew: accelerate the aircraft, maintain a satisfactory climb gradient and manage several configuration changes at the same time. To

help pilots fly their aircraft safely through the different steps of this phase of flight, some characteristic speeds were defined as maneuvering speeds. F, S and Green Dot speeds frame the aircraft climb performance limits.

PROCEDURES

Control your speed… during climb

F and S: Flaps and Slats minimum retraction speeds

Definitions

S speed is the minimum slats retraction speed, i.e. the minimum speed at which a clean confi guration should be selected.

F speed is the minimum speed at which fl aps should be retracted from CONF 3 or 2 to CONF 1+F.

It is represented by a green “F” on the PFD speed scale and displayed only when the slats / fl aps control lever is on position 3 or 2 (CONF 3 or 2) during the take-off phase, the initial climb and go-around (fi g.1). It is no longer displayed when in confi guration 1 or 1+F.

It is represented by a green “S” on the PFD speed scale and displayed only when the slats / fl aps control lever is on position 1 (CONF 1 and 1+F) (fi g.2).

How are F and S determined during the take-off phase?

In this respect, F speed allows a margin above the stall speed in the confi guration 1+F.

F speed varies according to the aircraft weight and altitude. It is tabulated in the Flight Envelope as a function of VS1g CONF 1+ F , which is the reference stall speed demonstrated by fl ight tests and agreed by the Airworthiness Authorities.

F speed = k x VS1g CONF 1+F , with k equal to about 1.18 to 1.26 VMCL + 5 kts ≤ F ≤ VFE CONF FULL – 2 kts

S speed varies according to the airIn this respect, S speed allows a marcraft weight and altitude. It is tabugin above the stall speed in the clean lated in the Flight Envelope as a funcconfi guration. tion of VS1g CLEAN CONF.

S = k x VS1g CLEAN CONF , with k equal to about 1.21 to 1.25

Green Dot (GD): best lift-to-drag ratio

Definition

GD speed is the engine-out operating speed in clean confi guration. In other words, it corresponds to the speed that allows the highest climb gradient with one engine inoperative in clean confi guration.

represents the operational speed of the clean confi guration and the recommended speed in holding in clean confi guration.

It is represented by a green dot on the PFD speed scale and displayed only when the slats / fl aps control lever is in the ‘0’ (CLEAN) position and landing gears are not compressed (fi g.3).

In all cases (all engines operative), the GD speed gives an estimate of the speed for best lift-to-drag ratio. It is also the fi nal take-off speed and it

How is GD determined?

GD speed is computed by the Autoflight systems and is based on the aircraft weight. The GD formula has been set up so that the resulting airspeed provides the best lift-to-drag ratio for a given altitude, air tempera-

ture and aircraft weight, in clean configuration with one engine out. In some phases of flight, GD is computed to minimize drag and thus, the fuel consumption (for example during the HOLD phase).

Limit speed

We have seen that deviations from the maneuvering speeds F, S and GD during climb can have an impact on the aircraft’s aerodynamic performance. We will now focus on the limit speed VFE.

VFE: Maximum speed with Flaps Extended

With the A/THR engaged and active (CLB / OP CLB / SPEED green on FMA), the aircraft remains below VFE.

When the A/THR is not active, VFE exceedance may occur (for example during a go-around).

Definition

VFE is the maximum speed with flaps extended. It has a specific value for each flap setting.

Generally speaking, the maximum speed defining the aircraft’s flight envelope is called VMAX. VMAX is equal to VLE (maximum speed with landing

How is VFE determined?

VFE is the maximum speed for high lift configurations, i.e. with slats / flaps extended: it is related to the structural limitation of the slats / flaps. A VFE is computed for each slats / flaps configuration, based on either the slats / flaps control lever position or the actual aircraft configuration (slats / flaps con-

gears extended) or VFE according to the aircraft configuration. VMAX is equal to VMO (or speed corresponding to MMO) only in the clean configuration. On the PFD speed scale, it corresponds to the lower end of the red and black strip (fig.4).

trol surfaces position), depending on the aircraft type.

In order to keep a sufficient margin between the VFE CONF 3 and the speed at which the next configuration is selected, the following inequality is met: VFE CONF 3 ≥ F + 10 kts.

PROCEDURES

Control your speed… during climb

MANAGING YOUR CLIMB: OPERATIONAL RECOMMENDATIONS

Flying a safe and steady climb requires pilots’ attention to carefully manage the different configuration changes, while accelerating to the en-route climb speed and eventually, cruise speed.

Indeed, not respecting the maneuvering and limit speeds leads to adverse consequences that we will review. Avoiding an overspeed situation during the slats / flaps retraction - with its potential structural damage conse-

quences - is important. It is therefore worth understanding the different VFE display logics implemented in each aircraft family, and the resulting overspeed aural warning behaviour during the climb.

What are the operational implications of not respecting the maneuvering or limit speeds?

F and S: Flaps and Slats minimum retraction speeds

F speed (resp. S) is defined as the recommended minimum flaps (resp. slats) retraction speed. Retracting the flaps (resp. slats) at a speed significantly lower than F (resp. S) would reduce the margin against the high Angle-Of-Attack (AOA) protection. This could lead the aircraft to reach a speed below the lowest selectable speed VLS CONF 1 (or 0), and possibly low enough to break through the high AOA protection threshold.

Retracting the flaps (resp. slats) at a speed significantly higher than F speed (resp. S) would reduce the climb performance and thus, possibly compromise the aircraft ability to clear any obstacles (this is more likely if one engine is inoperative). If flaps need to be maintained for a turn before acceleration altitude for instance, F speed (resp. S) can be used safely to perform a turn while climbing.

GD: Green Dot

GD IN A NUTSHELL Avoid flying below GD during climb.

At a given weight and engine rating, the potential climb gradient is maximum when (Thrust – Drag) is at a maximum - i.e. when the lift-to-drag ratio is maximum.

Deviating below GD involves an increase in the drag on the aircraft and would eventually undermine the aircraft’s ability to continue a climb. Indeed, if the aircraft speed goes significantly below GD, with the maximum available thrust already in use (assuming that thrust levers have just

been set to CLIMB / MCT), then the only way for the crew to recover a satisfactory climb gradient is to decrease the rate of climb (even enter a descent if necessary) in order to accelerate to or above GD. This maneuver is obviously counteractive to the objectives of the climb phase.

Therefore in the clean configuration, the crew should not fly below GD in order to avoid degrading climb performance.

VFE: Maximum speed with flaps extended

In case of take-off with A/THR not active, flying with slats / flaps extended, or extending slats / flaps well above VFE directly poses a risk of structural damage through the slats / flaps track mechanisms. This may result in distortion of the flaps and slats or the extension mechanism or even the aircraft structure upstream. In case VFE is exceeded, an overspeed aural warning is triggered in the cockpit in order to alert the crew.

The flight crew will have to reduce the speed or to retract the slats / flaps accordingly.

Exceeding VFE may subsequently trigger inspections of the slats/ flaps mechanism and/or the aircraft structure.

Specific trouble shooting procedures exist to inspect and repair an aircraft after flight above VFE. These procedures are available in the Aircraft Maintenance Manual (AMM).

VFE IN A NUTSHELL Do not fly with slats / flaps extended above VFE.

How to avoid an overspeed during slats / flaps retraction?

Avoiding an overspeed during slats / flaps retraction relies on a variety of complementary aspects. Procedures, pilots’ attention and coordination, anticipation of configuration

changes, understanding of the limit speed and of the different VFE display logics and overspeed aural warning behaviour implemented in each aircraft family.

The common approach

Slats and flaps retraction during climb can be managed safely by following SOP, and observing the visual F and S indications on the PFD. Incidentally, doing so allows the crew to respect the VFE indication displayed on the PFD and thus, avoid triggering an aural overspeed warning (with potential structural damage). The use of A/THR also enables the crew to avoid an overspeed condition during slats / flaps retraction.

While the PF is expected to manage these configuration changes, the PM plays a key role in facilitating his/her

task by anticipating them. During the initial climb phase, the PM needs to be vigilant to speed trends and alert the PF in case the margin that is left against the applicable limit speed VFE becomes too tight. This is valid at all time, for all aircraft families.

Differences arise when we look more closely at the VFE display logics for each family. In particular, we want to emphasize the possibility of a temporary, yet inconsequential, overspeed aural warning on A300/A310, A320 and A330/A340 Families.

PROCEDURES

Control your speed… during climb

The case of untimely temporary overspeed aural warning during slats / flaps retraction

A300/A310, A320 and A330/A340 Families

• On A300/A310, A320 and A330/ A340 Families,

• The VFE value displayed on the PFD is based on the slats / flaps control lever position and it moves by one step as soon as this lever is moved.

• The overspeed aural warning triggering threshold varies according to the actual aircraft configuration, i.e. the slats / flaps surfaces real time position.

Therefore, during slats / flaps transition, the dynamic acceleration of the airplane may lead to a temporary OVERSPEED WARNING even if the current speed is out of the red and black strip displayed on the PFD. In this situation, there are neither operational consequences nor safety issues.

This is due to the following logic:

• When the flap lever is moved from CONF 2 (or 3) to CONF 1+F, F speed could be very close to VFE before flaps retraction. Once the flap retraction is initiated, VFE CONF (2 or 3) moves in one step to VFE CONF 1+F before the flaps actually reach CONF 1+F. As a consequence, in acceleration towards S speed, the VFE aural warning could activate although the actual surfaces speed is below the displayed VFE.

• When the flap lever is moved from CONF 2 (or 3) to CONF 1+F, S speed could be greater than VFE CONF 1+F before the surfaces retract. When automatic flap retraction occurs, the barbers pole does not move before the flaps fully retract.

A350 and A380 Families

On A350 and A380 Families, a different logic was developed. The VFE display on the PFD is directly based on the actual aircraft configuration, as is the overspeed aural warning trigger-

ing threshold. This means that the two signals are perfectly synchronized, thus the risk of an untimely temporary overspeed warning is eliminated.

The case of temporary overspeed aural warning during slats / flaps retraction after a heavy-weight take-off

BEST PRACTICE

After a heavy-weight take-off, do not delay slats / flaps 0 selection above S speed in order to prevent possible temporary VFE overspeed aural warning.

In the particular case of a heavyweight take-off, the risk of a temporary overspeed aural warning is increased. Indeed, in this configuration, S speed is quite close to VFE CONF 1+F because the aircraft weight is higher and the lift needed to climb is higher too. Therefore the slats need to remain extended for longer. As a result, the crew will order flaps retraction at a speed that might be higher than the Flaps Auto-retraction speed. In that case, should the acceleration of the airplane be rapid, a VFE aural warning may momentarily trigger. This logic is as per design and structural limits are not encountered.

For example, an A320 at a Take-Off Weight (TOW) of 76T, S speed of 205 kts, the pilot will order flaps retraction most probably at or slightly above 210 kts, which is precisely the Flaps Auto-retraction speed. Once the slats / flaps control lever is in the retracted position, the VFE red and black strip is no longer displayed on the PFD speed scale. If the airplane accelerates rapidly, then the airspeed may catch up the actual instantaneous VFE momentarily, which will trigger the VFE aural warning.

Again, this logic is as per design and structural limits are not encountered.

During climb, in manual flight, the main risk is to experience an aural overspeed warning (with potential structural damage) as a result of a late slats / flaps retraction. Understanding the implications of climb speeds is paramount to enable pilots to sense instantly the available margin they have left to avoid exceeding the limit slats / flaps retraction speed.

In practice, once the aircraft is airborne, pilots must be fully cognisant of the airspeed as well as the speed trends at all time in flight.

DID YOU KNOW

To know more about speeds, read our brochure “Getting to grips with aircraft performance”, available on AirbusWorld.

A presentation was also made at the 11th Perf and Flight Ops Conference in Dubai in 2011.

---

中文译文

006 Safety First #20 | 2015年7月 程序

控制你的速度……在爬升阶段

本系列第二篇文章延续上期杂志#18开始的速度控制主题，我们已起飞并进入爬升阶段。主要目标是以适当的速度收上缝翼/襟翼，同时保持足够的升力以完成加速和爬升。

洛琳·德·博杜斯（LORRAINE DE BAUDUS）

飞行运行标准与安全管理

菲利普·卡斯坦（PHILIPPE CASTAIGNS）

试飞员

起飞后，飞机继续爬升并飞离繁忙空域。机组的目标是加速至航路爬升速度，同时管理各种飞机构型变化，通常包括起落架、缝翼和襟翼的收上，以及从起飞功率向爬升功率的转换。

本文旨在阐明爬升阶段使用的不同机动速度和限制速度是如何定义和确定的，以及如何在日常运行中实施。

管理你的爬升：了解速度

爬升通常以空速飞行，该空速最初常受空中交通管制（ATC）指令限制。为在这些限制条件下安全管理爬升阶段，一些特征速度是有用的工具，需要密切监控。具体应监控哪些速度？这些速度意味着什么？如果超过会怎样？

每次飞行，特征速度由飞机自动飞行系统（飞行管理系统（FMS）、飞行引导（FG）和飞行包线（FE））自动计算，并有效地显示在主飞显示器（PFD）空速刻度上。它们作为机动速度和限制速度，极具实用价值，可安全引导飞行员在爬升阶段做出构型转换决策。

我们的目标是突出空客向飞行机组发布的关于爬升阶段速度监控的所有建议背后的设计和运行考虑。

缝翼（Flaps, F）、襟翼（Slats, S）和绿点（Green Dot, GD）机动速度与其他参数一样，是机组在FMS初始化时输入的零燃油重量（ZFW）的函数。因此，任何错误的输入都会影响这些速度。

F、S和绿点速度限定了飞机爬升性能限制。

机动速度

在正常条件（所有发动机工作）下，爬升阶段给机组带来一些挑战：加速飞机、保持令人满意的爬升梯度，同时管理多项构型变化。为帮助飞行员安全飞越该飞行阶段的不同步骤，一些特征速度被定义为机动速度。F、S和绿点速度限定了飞机爬升性能限制。

程序

控制你的速度……在爬升阶段

F 和 S：襟翼和缝翼最小收上速度

定义

S 速度是缝翼最小收上速度，即应选择清洁构型的最小速度。

F 速度是从构型 3 或 2 将襟翼收至构型 1+F 的最小速度。

它以PFD速度刻度上的绿色“F”表示，仅在起飞阶段、初始爬升和复飞期间缝翼/襟翼控制手柄位于位置 3 或 2（构型 3 或 2）时显示（图1）。当处于构型 1 或 1+F 时不再显示。

它以PFD速度刻度上的绿色“S”表示，仅在缝翼/襟翼控制手柄位于位置 1（构型 1 和 1+F）时显示（图2）。

起飞阶段 F 和 S 如何确定？

就此而言，F 速度允许构型 1+F 失速速度以上有一定的余度。

F 速度随飞机重量和高度变化。它以飞行包线中构型 1+F 的VS1g参考失速速度为函数编制成表，该参考失速速度由飞行试验演示并经适航当局认可。

F 速度 = k × VS1g 构型 1+F，其中 k 约为 1.18 至 1.26 VMCL + 5 kts ≤ F ≤ VFE 构型全 + 2 kts

S 速度随飞机重量就此而言，S 速度允许清洁和高度变化。它以飞行包构型失速速度以上有一定的线中清洁构型 VS1g 为函余度。数编制成表。

S = k × VS1g 清洁构型，其中 k 约为 1.21 至 1.25

绿点（GD）：最佳升阻比

定义

GD 速度是清洁构型下的单发失效运行速度。换言之，它对应的是在清洁构型下单发失效时能获得最大爬升梯度的速度。

它代表清洁构型的运行速度，也是清洁构型下等待的推荐速度。

它以PFD速度刻度上的绿点表示，仅当缝翼/襟翼控制手柄处于“0”（清洁）位置且起落架未压缩时显示（图3）。

在所有情况下（所有发动机工作），GD 速度给出最佳升阻比速度的估算值。它也是最终起飞速度且

GD 是如何确定的？

GD 速度由自动飞行系统根据飞机重量计算得出。GD 计算公式的设定原则是：在给定高度、气温和飞机重量条件下，以单发失效、光洁形态飞行时，使升阻比达到最优从而提供最佳空速。在某些飞行阶段，GD 的计算以最小阻力（因此也最小化燃油消耗）为目标（例如在等待阶段）。

限制速度

我们已经看到，在爬升过程中偏离机动速度 F、S 和 GD 会对飞机的气动性能产生影响。现在我们把重点放在限制速度 VFE 上。

VFE：放下襟翼时的最大速度

当 A/THR 接通且处于激活状态（FCU 上 FMA 显示 CLB/OP CLB/SPEED 绿色）时，飞机保持在 VFE 以下。

当 A/THR 未激活时，可能会发生超 VFE 情况（例如在复飞期间）。

定义

VFE 是放下襟翼时的最大速度。每个襟翼设置对应一个特定的 VFE 值。

一般来说，定义飞机飞行包线的最大速度称为 VMAX。VMAX 等于 VLE（放下起落架时的最大速度）或根据飞机形态等于 VFE。在 PFD 速度带上，它对应红黑条纹的下端（图 4）。

VFE 是如何确定的？

VFE 是高升力形态（即缝翼/襟翼伸出时）的最大速度：它与缝翼/襟翼的结构限制有关。每种缝翼/襟翼形态都会计算一个 VFE 值，计算依据可以是缝翼/襟翼控制手柄的位置或飞机实际构型（缝翼/襟翼控制面的位置），具体取决于飞机型号。

为了在 VFE CONF 3 与选择下一形态时的速度之间保持足够的余量，需满足以下不等式：VFE CONF 3 ≥ F + 10 节。

程序

控制您的速度……在爬升阶段

管理您的爬升：运行建议

执行安全稳定的爬升需要飞行员仔细管理各种形态变化，同时加速至航路爬升速度并最终达到巡航速度。

事实上，不遵守机动速度和限制速度会导致不良后果，我们将对此进行回顾。避免在缝翼/襟翼收回过程中出现超速情况——及其潜在的结构损坏后果——非常重要。因此，理解每种机型系列中实施的不同 VFE 显示逻辑，以及爬升过程中由此产生的超速音响警告行为是非常值得的。

不遵守机动速度或限制速度会有什么运行后果？

F 和 S：襟翼和缝翼最小收回速度

F 速度（相应地 S 速度）定义为建议的最小襟翼（相应地缝翼）收回速度。如果以显著低于 F（相应地 S）速度收回襟翼（相应地缝翼），会降低高迎角（AOA）保护的裕度。这可能导致飞机速度降至低于最低可选速度 VLS CONF 1（或 0），甚至可能低到突破高 AOA 保护阈值。

如果以显著高于 F 速度（相应地 S）收回襟翼（相应地缝翼），会降低爬升性能，从而可能危及飞机越过障碍的能力（在单发失效情况下更可能发生）。例如，如果在加速高度前需要保持襟翼进行转弯，F 速度（相应地 S 速度）可以安全地用于边爬升边转弯。

GD：绿色点

GD 概要 避免在爬升时低于 GD 飞行。

在给定的重量和发动机额定值下，当（推力 - 阻力）最大时——即升阻比最大时——潜在爬升梯度达到最大值。

低于 GD 会导致飞机阻力增加，最终会削弱飞机继续爬升的能力。事实上，如果飞机速度显著低于 GD，而最大可用推力已经在使用中（假设推力手柄刚设置为 CLIMB/MCT），那么机组恢复满意爬升梯度的唯一方法是降低爬升率（必要时甚至进入下降），以加速至 GD 或以上。这一机动显然与爬升阶段的目标背道而驰。

因此，在光洁形态下，机组不应低于 GD 飞行，以免爬升性能下降。

VFE：放下襟翼时的最大速度

如果 A/THR 未激活起飞，以缝翼/襟翼伸出的形态飞行，或将缝翼/襟翼伸出远超 VFE，会直接通过缝翼/襟翼滑轨机构带来结构损坏风险。这可能导致襟翼和缝翼或伸出机构甚至上游飞机结构变形。如果超过 VFE，驾驶舱会触发超速音响警告以提醒机组。

飞行机组需要相应地减速或收回缝翼/襟翼。

超 VFE 后可能触发对缝翼/襟翼机构和/或飞机结构的检查。

飞行后超出 VFE 的检查和修理有专门的故障排除程序。这些程序可在 aircraft maintenance manual（AMM）中找到。

VFE 概要 不要以缝翼/襟翼伸出状态在 VFE 以上飞行。

如何避免在缝翼/襟翼收起时发生超速？

避免在缝翼/襟翼收起时发生超速，需要多方面相互配合：程序、飞行员的注意力和协调、对构型变化的预判、对限制速度的理解，以及对各机型所采用的VFE显示逻辑和超速音响警告行为特点的掌握。

通用方法

在爬升阶段，通过遵循SOP并观察PFD上的F和S指示，可以安全地完成缝翼和襟翼的收起。附带地，这样做可使机组遵守PFD上显示的VFE指示，从而避免触发超速音响警告（可能导致结构损伤）。使用A/THR（自动推力）也能使机组在缝翼/襟翼收起期间避免超速状况。

当PF负责管理这些构型变化时，PM通过预判构型变化在协助其任务方面发挥关键作用。在初始爬升阶段，PM需要对速度趋势保持警惕，并在剩余的适用限制速度VFE余度变得过小时提醒PF。这适用于所有时候，适用于所有机型系列。

当我们更仔细地查看各机型的VFE显示逻辑时，会发现差异。特别是，我们要强调A300/A310、A320和A330/A340系列飞机上可能出现短暂的、无后果的超速音响警告的可能性。

程序

控制你的速度……在爬升阶段

缝翼/襟翼收起期间意外出现短暂超速音响警告的情况

A300/A310、A320和A330/A340系列

• 在A300/A310、A320和A330/A340系列飞机上，

• PFD上显示的VFE值基于缝翼/襟翼控制手柄的位置，一旦移动该手柄，VFE值就会移动一步。

• 超速音响警告触发阈值根据实际飞机构型（即缝翼/襟翼表面的实时位置）而变化。

因此，在缝翼/襟翼过渡期间，飞机的动态加速可能导致短暂的OVERSPEED WARNING（超速警告），即使当前速度处于PFD上显示的红黑条范围之外。在这种情况下，既没有运营后果，也没有安全问题。

这是由于以下逻辑：

• 当襟翼手柄从CONF 2（或3）移动到CONF 1+F时，在襟翼收起之前，F速度可能非常接近VFE。一旦开始襟翼收回，VFE CONF（2或3）会在襟翼实际到达CONF 1+F之前一步移动到VFE CONF 1+F。因此，在向S速度加速过程中，VFE音响警告可能会被激活，即使实际表面速度低于显示的VFE。

• 当襟翼手柄从CONF 2（或3）移动到CONF 1+F时，在表面收起之前，S速度可能大于VFE CONF 1+F。当自动襟翼收回发生时， barber’s pole（红针）在襟翼完全收起之前不会移动。

A350和A380系列

在A350和A380系列飞机上，采用了一种不同的逻辑。PFD上的VFE显示直接基于实际飞机构型，超速音响警告触发阈值也是如此。这意味着两个信号完全同步，因此消除了意外出现短暂超速警告的风险。

缝翼/襟翼收起期间在重起飞后出现短暂超速音响警告的情况

最佳做法

在重起飞后，不要在S速度以上延迟选择缝翼/襟翼0，以防止可能出现的短暂VFE超速音响警告。

在重起飞的特殊情况下，出现短暂超速音响警告的风险会增加。实际上，在该构型下，由于飞机重量较大且爬升所需升力较高，S速度非常接近VFE CONF 1+F。因此，缝翼需要保持伸展更长时间。结果，机组将在可能高于自动襟翼收起速度的速度下令襟翼收回。在这种情况下，如果飞机加速较快，VFE音响警告可能会瞬间触发。此逻辑符合设计意图，不会遇到结构限制。

例如，对于起飞重量（TOW）为76吨的A320，S速度为205节，飞行员很可能在210节或略高于210节的速度下令襟翼收回，这恰恰是自动襟翼收起速度。一旦缝翼/襟翼控制手柄处于收起位置，PFD速度刻度上就不再显示VFE红黑条。如果飞机加速较快，则空速可能暂时赶上实际的瞬时VFE，这将触发VFE音响警告。

同样，此逻辑符合设计意图，不会遇到结构限制。

在爬升阶段，在人工飞行中，主要风险是由于延迟收起缝翼/襟翼而导致音响超速警告（可能造成结构损伤）。了解爬升速度的含义对于使飞行员能够即时感知剩余可用的余度以避免超过限制性的缝翼/襟翼收起速度至关重要。

在实践中，一旦飞机离地，飞行员必须在整个飞行过程中始终充分了解空速和速度趋势。

你知道吗

要了解更多关于速度的知识，请阅读我们的小册子《Getting to grips with aircraft performance》（掌握飞机性能），该手册可在AirbusWorld上获取。

2011年，还在迪拜举行的第11届性能与飞行运营大会上进行了相关演示。