A320 Tail strike at Take-Off?

Source: Airbus Safety First URL: https://safetyfirst.airbus.com/a320-tail-strike-at-take-off/ Published: 2007-12-14 Magazine Issue: 2007-12 Category: Archive PDF: Original PDF

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By: Marc Baillion Flight Safety Manager

1 Introduction

The engineering department analysed the Flight Data Monitoring and reported to Airbus as follows: “The FDM trace shows a maximum pitch angle of 16.52 degrees nose up, with both main gears on the ground (presumably at least partially compressed), and the nose wheel is in the air. Even if the main gear was fully extended, a strike should have occurred at 13.5 degrees.

This article describes an event that was first thought to be a tail strike. Further investigation allowed the operator to dismiss this belief. The subsequent analysis of this occurrence brought three interesting points to highlight, from which lessons can be drawn. These experiences are particularly addressed to the cockpit, cabin crews as well as to the engineers in charge of analyzing flight data.

Assuming that the runway undulations were not a factor, it would appear that either the FDM software, or the data provided in the FCOM Bulletin No.22/4, is inaccurate.”

2 Descri ion pt of the event

The airline reported no sign on the aircraft aft lower fuselage indicative of a tail strike.The take-off weight and center-of-gravity location were inside the normal envelope. The operator kindly provided Airbus with a copy of the DAR data.

At rotation, a member of the crew in the rear galley felt a thump and heard a bang at the rear of the aircraft. This information was forwarded to the cockpit crew when the aircraft had reached FL 160. At this time, the crew contacted the tower, which initiated a runway inspection, but found no sign of a tailstrike. They then consulted with the airline’s engineering department and decided to divert the aircraft. After landing, it appeared that about 20 bags had shifted in the rear hold.

3 Anal sis of the event y and lessons learned

Take-off was performed in the following conditions: Configuration 3 Thrust levers position was set to TOGA TO weight: 73.690 T TO center-of-gravity: 31% Stabilizer position: 0.5° down V1 = 123 kts VR = 133 kts V2 = 138 kts

3.1 Stick inputs and rotation

Rotation was initiated at the expected VR. Analysis of the DAR data shows that about half forward stick was applied until 80 kts, as per SOP. When the stick was released (at approx. 100 kts) the aircraft experienced a pitch attitude increase of +1°.

The rotation was initiated through a square input of about 1/2 full back stick deflection (-8° of stick) that was then slightly increased (up to -9° of stick) and maintained.

A subsequent calculation of the event lift-off conditions was conducted, using as inputs: longitudinal sidestick inputs, THS trim position, a/c weight and center-of-gravity, TO configuration, thrust lever position. The calculation results correlate well with the 12-13 degrees at lift-off and confirm also that a high pitch rate (5°/sec) was achieved, while the minimum distance between the tail and the runway was 2 feet.

A too high rotation rate is one of the main causes of tail strike at take-off and should therefore be avoided. Airbus recommends adhesion to the Flight Operation Briefing Note titled “Take-off and departure operations - Preventing tailstrike at takeoff”, which states:

“At VR, the flight crew should initiate the rotation with a smooth positive backward sidestick input to achieve a continuous rotation rate of approximately 3°/sec. Avoid aggressive and sharp inputs.”

See also FCOM bulletin 806/1 “Avoiding Tailstrike”.

Under these conditions, the A/C initiated its rotation at about +1.4°/sec before stabilizing at a rotation rate of about +5°/sec, whereas the recom - mended value, as per SOP, is 3°/sec.

3.2 Cabin-to-cockpit communications

According to the crew report, the purser informed the cockpit at FL160, and not before, because of the application of a sterile cockpit concept by this operator.

In the event of a tailstrike, the abnormal and emergency procedures call for LAND ASAP and MAX FL100 (see hereafter), in order to avoid cabin depressurization:

Airbus’ “Getting to Grips with Cabin Safety”, chapter 9 “Crew Resource Management” recommends that “any situation, feeling, word, behavior, observation that alerts cabin crewmembers to a possible threat to flight safety, must immediately be reported to the purser and the flight crew.”

For good crew coordination, training should include instructing flight crewmembers and flight attendants on each other’s emergency procedures, codes, signals, and safety-related duties.

ABNORMAL AND EMERGENCY 3.02.80 P 21 MISCELLANEOUS SEQ 001 REV 39 TAILSTRIKE In the event of a tailstrike, apply the following procedure :

• LAND ASAP

• ] MAX FL … … … … … … … … … … … . . 100 or MSA 500 feet/minute should be targeted for the climb, to minimize pressure changes, and for passenger and crew comfort. Similarly, the rate of descent must be limited to about 1000 feet/minute, except for the final approach that must be performed normally. Notify the ATC of the aircraft’s rate of climb.

• ] RAM AIR … … … … … … … … … … … … … . . ON ] PACK 1 and 2 … … … … … … … … … … … … . OFF

The sterile cockpit concept comes from FAR 121/542, which among others, prohibits non essential communications between the cabin and cockpit crews below 10 000ft. This regulation may explain why cabin crews may hesitate to report occurrences which have no obvious safety implications. A concern addressed by Advisory Circular AC 120-48, which states: “hesitancy or reluctance on the part of a flight attendant to contact the flight crewmembers with important safety information because of a misconception of the sterile cockpit rule is potentially even more serious that the unnecessary distraction caused by needless violations of the sterile cockpit”.

Conducting joint crew briefings will help in creating a working environment that is more conducive to a safe operation:

• Cabin crewmembers should be encouraged to report to the purser, or the flight crew, anything that they feel may pose a threat to the safety of the flight

• Discuss the “Sterile Cockpit” rule with the pilots, and the circumstances that are acceptable for contacting the flight crew during this time

See also CCOM chap 08.045 “SOP Preflight Briefing”.

3.3 Determination of the lift-off time when analyzing flight data monitoring information

The flight data analysts of this particular airline wondered how the aircraft could have reached a nose up pitch angle of 16.5 degrees, “with both main gears on the ground (presumably at least partially extended)”, without striking the tail, considering that the FCOM calls for a pitch limitation of 11.7 degrees with the MLG fully compressed and 13.5 degrees with the MLG fully extended.

The explanation lies in the fact that the main gears were in fact not on the ground any more when the pitch reached the 16,5 degrees. The reason for the confusion lies in the time difference, due to the gears’ damping function, between the actual lift-off time and the MLG full extension.

The actual lift-off can be reasonably well determined by the aircraft normal load factor variation. Recorded data shows that when the load factor began to increase, the pitch angle was in the range of 12 to 13 degrees i.e. within the published limitations for the A320 (as per FCOM bulletin 806/1).

4 Conclusion

This event did not jeopardize the safe continuation of the flight, but the conducted investigation allowed to highlight some shortcomings, which could have led to a critical situation.

Lessons can be drawn from this occurrence for the benefit of all operators in the following fields: - Rotation technique

• Cabin to crew communication

• Understanding DFDR data This illustrates the benefit of reporting events for the advancement of safety.

Airbus safety and operational materials, including the Flight Operation Briefing Notes and Getting to Grips with… brochures, can be found in the Flight Operations section of the secure area of www.airbusworld.com.

Alternatively, the FOBNs can be consulted at www.airbus.com/en/corporate/ethics/safety_lib/

A further analysis has been performed by Airbus to substantiate the time difference between the actual lift-off time and the MLG full extension. A flight test A320 was equipped with MLG load measurements and the results fully confirm the good correlation of the actual lift-off time with the normal load factor variation. The full extension of the MLG may take place more than 2 seconds later, depending on the aircraft weight and centerof-gravity location. This confirmed that the use of the gear squat parameters[1] is not accurate enough to give precise lift-off times.

1 RHSQUAT and LHSQUAT parameters shift to zero when, respectively RH and LH MLG are fully extended.

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中文译文

来源: Airbus Safety First 网址: https://safetyfirst.airbus.com/a320-tail-strike-at-take-off/ 发布日期: 2007-12-14 杂志期号: 2007-12 类别: 档案 PDF: Original PDF

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作者：Marc Baillion 飞行安全经理

1 引言

工程部门分析了飞行数据监控（FDM）数据，并向空客报告如下：“FDM轨迹显示最大俯仰角为16.52度抬头，两个主起落架在地面上（估计至少部分被压缩），且前轮已离地。即使主起落架完全伸展，在13.5度时也应发生擦尾。”

本文描述了一起最初被认为是擦尾的事件。进一步调查使运营商得以排除这一判断。对该事件的分析带来了三个值得关注的问题，并可从中汲取经验教训。这些经验特别适用于驾驶舱、客舱机组人员以及负责分析飞行数据的工程师。

假设跑道起伏不是影响因素，那么看来FDM软件或FCOM公告第22/4期提供的数据可能存在不准确之处。

2 事件描述

航空公司报告飞机后下部机身没有任何擦尾痕迹。起飞重量和重心位置均在正常范围内。运营商向空客提供了DAR数据副本。

在抬轮时，后厨房的一名乘务员感觉到飞机后部传来撞击声并听到一声巨响。该信息在飞机达到FL160时传达给了驾驶舱机组。此时，机组联系了塔台，塔台进行了跑道检查，但未发现擦尾痕迹。随后他们与航空公司工程部门协商，决定让飞机备降。着陆后，发现后货舱约有20件行李发生了位移。

3 事件分析与经验教训

起飞在以下条件下执行：构型3，推力手柄位置设置为TOGA，起飞重量：73.690 T，起飞重心：31%，水平安定面位置：0.5°下偏，V1 = 123 kts，VR = 133 kts，V2 = 138 kts

3.1 侧杆输入与抬轮

抬轮在预期的VR速度启动。对DAR数据的分析显示，按照标准操作程序（SOP），在约80节前施加了约一半的前推侧杆。当侧杆在约100节时被释放，飞机经历了+1°的俯仰姿态增加。

抬轮通过约二分之一满后拉侧杆偏转（-8°侧杆）的阶跃输入启动，随后略微增加（至-9°侧杆）并保持。

随后利用以下输入参数对该事件进行了抬轮条件的计算：纵向侧杆输入、THS配平面位置、飞机重量和重心、起飞构型、推力手柄位置。计算结果与抬轮时的12-13度吻合良好，同时也确认达到了5°/秒的高俯仰率，而尾部与跑道之间的最小距离为2英尺。

过高的抬轮率是起飞时擦尾的主要原因之一，因此应予以避免。空客建议遵守《起飞与离场操作——防止起飞擦尾》飞行操作简报中的规定：

“在VR时，机组应通过平稳的正向后拉侧杆输入启动抬轮，以实现约3°/秒的持续抬轮率。避免激进和急促的输入。”

另请参阅FCOM公告806/1”避免擦尾”。

在这些条件下，飞机在约+1.4°/秒开始抬轮，随后稳定在约+5°/秒的抬轮率，而按SOP建议的值为3°/秒。

3.2 客舱-驾驶舱通信

根据机组报告，乘务长在FL160时才通知驾驶舱，此前未进行通报，原因是该运营商实施了无菌驾驶舱概念。

发生尾撬擦地时，不正常和紧急程序要求尽快着陆和最大飞行高度100（见下文），以避免客舱释压：

空客《客舱安全手册》第9章”机组资源管理”建议：“任何使客舱乘务员意识到可能威胁飞行安全的情况、感受、言语、行为或观察，必须立即报告给乘务长和飞行机组。”

为了实现良好的机组协调，培训应包括向飞行机组和客舱乘务员相互介绍彼此的紧急程序、代码、信号和安全相关职责。

不正常和紧急情况 3.02.80 P 21 杂项 序列 001 修订 39 尾撬擦地 发生尾撬擦地时，执行以下程序：

• 尽快着陆

• 最大飞行高度 … … … … … … … … … … … … … … . 100 或 MSA

爬升时爬升率目标约为500英尺/分钟，以最大程度减小压力变化，确保乘客和机组人员的舒适度。同样，下降率必须限制在大约1000英尺/分钟，除正常执行的最终进近外。应将飞机的爬升率通知ATC。

• 冲压空气 … … … … … … … … … … … … … … … … … 接通 ] 组件1和2 … … … … … … … … … … … … … … … … … … . . 关闭

无菌驾驶舱概念源于FAR 121.542，该规定禁止客舱与驾驶舱机组之间在10000英尺以下进行非必要通信。这一规定可能导致客舱乘务员犹豫是否报告没有明显安全影响的异常事件。咨询通告AC 120-48 addressing addressing addressing了这一问题，其中指出：“由于对无菌驾驶舱规则的误解，乘务员犹豫或不愿与飞行机组联系重要安全信息，其潜在危害可能比不必要的无菌驾驶舱违规造成的干扰更为严重。”

开展联合机组简令有助于营造更有利于安全运行的工作环境：

• 应鼓励客舱乘务员向乘务长或飞行机组报告他们认为可能对飞行安全构成威胁的任何情况

• 与飞行员讨论”无菌驾驶舱”规则，以及在此期间联系飞行机组可接受的情况

另见CCOM第08.045章”标准操作程序起飞前简令”。

3.3 分析飞行数据监控信息时确定抬轮时刻

该航空公司飞行数据分析师想知道，飞机如何在”主起落架仍在地面上（据推测至少部分伸展）“的情况下达到16.5度的俯仰角而不擦地，考虑到FCOM规定MLG完全压缩时俯仰限制为11.7度，完全伸展时为13.5度。

解释在于，当俯仰角达到16.5度时，主起落架实际上已不再接触地面。混淆的原因在于，由于起落架的阻尼功能，实际抬轮时刻与MLG完全伸展时刻之间存在时间差。

实际抬轮可以通过飞机法向载荷因子的变化相当准确地确定。记录数据显示，当载荷因子开始增加时，俯仰角在12至13度范围内，即在A320公布限制范围内（根据FCOM公报806/1）。

4 结论

该事件并未危及航班的安全继续，但进行的调查揭示了一些不足之处，这些不足可能导致危急情况。

可以从该事件中为所有运营商汲取以下方面的经验教训：- 抬轮技术

• 客舱与机组通信

• 理解DFDR数据

这说明了报告事件对促进安全的益处。

空客安全和操作资料，包括飞行运行简报笔记和”Getting to Grips with…”系列手册，可在www.airbusworld.com安全区域的飞行运行部分找到。

或者，可以在www.airbus.com/en/corporate/ethics/safety_lib/查阅飞行运行简报笔记。

空客进行了进一步分析，以证实实际抬轮时刻与MLG完全伸展之间的时间差。一架飞行测试A320配备了MLG载荷测量装置，结果完全证实了实际抬轮时刻与法向载荷因子变化之间的良好相关性。MLG完全伸展可能延迟2秒以上，取决于飞机重量和重心位置。这证实了使用起落架squats参数[1]不足以提供精确的抬轮时刻。

1 RHSQUAT和LHSQUAT参数分别在右和左MLG完全伸展时变为零。