【27飞行操纵】维护提示 | 襟翼位置指示器故障导致襟翼不对称锁死
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之前有位机长向我反映过一个故障：
某737NG飞机，空中襟翼锁死，机务工程部门最后排故分析下来是襟翼位置指示表故障，导致后缘襟翼不工作。
Q：输出为什么会影响输入呢？
按我们的常规思维，襟翼位置传感器是用来指示的，它故障了也就是指示不准呗，怎么还会导致襟翼锁死呢？
后来我看下了，波音在2017年10月9日发布了一个FTD，刚好说了此问题：
737NG-FTD-27-17002
Flap System Shutdowns Due to Sensed Asymmetry
这类故障通常在FSEU自检存储有代码：27-52259或27-52260，或27-52261。而且地面通常无法再现出来。
最近刚好看到几起这样的故障，在此简单说明下这个问题。
一、背景介绍
某737-800飞机，AirFASE 远程监控到左右襟翼位置不一致，最大7，左慢右快。
更换右襟翼位置传感器，完成襟翼位置传感器校装，仍然监控到报警。
更换左襟翼位置传感器。继续监控到左右差值最大9.84，但未产生锁定。重新完成左侧襟翼位置传感器校装，仍然一直在报警。
与另一架飞机对倒FSEU监控。
后续某次航班落地前机组反映空中左右襟翼放不出。襟翼位置指示：左侧放出一点，右侧放出不到1单位。
AHM监控到左侧放出13°，右侧放出24°，造成锁定。
注：译码和报文参数单位都是°，飞机表头上指示单位是UNIT。13°和24°换成飞机上的指示都是很小的值。
报文参数说明：
ASAD - Average sum of absolute deltas
APV - Average parameter value
PMAX - Peak maximum parameter value
PMIN - Peak minimum parameter value
TEFSK1P - Trailing edge flap skew 1 position
TEFSK2P - Trailing edge flap skew 2 position
TEFSK3P - Trailing edge flap skew 3 position
TEFSK4P - Trailing edge flap skew 4 position
TEFSK18M - Trailing edge flap skew 1 8 margin
TEFSK27M - Trailing edge flap skew 2 7 margin
TEFSK8P - Trailing edge flap skew 8 position
TEFSK7P - Trailing edge flap skew 7 position
TEFSK6P - Trailing edge flap skew 6 position
TEFSK5P - Trailing edge flap skew 5 position
TEFSK36M - Trailing edge flap skew 3 6 margin
TEFSK45M - Trailing edge flap skew 4 5 margin
LVRPOSN - Lever position
LFP - Left flap position
RFP - Right flap position
TEFAMM - Trailing edge asym margin
FSEU自检，故障代码27-52259，L FL POS +13.3.PIN K7和PIN K8代码信息。
地面拆下襟翼位置表头电插头，重新放襟翼到40度，再次收上正常。排故更换左襟翼位置传感器和襟翼位置指示表头，后续监控正常。
二、原因分析
襟翼位置传感器：左右各一个襟翼位置传感器安装在1 号和8 号齿轮盒的末端，传感器的量程为0 到270度。
↑ 襟翼位置传感器，左右各一个
在襟翼收上时为0 度，放下到40 单位时为270度。它实际上是感受扭力管转动了多少转，它这一度的变化对应扭力管转了多少转。
每个传感器有三个同步器，也就是三组线圈，分别给自动驾驶系统，失速保护系统和后缘襟翼指示系统提供信号。
襟翼位置传感器中间通过FSEU并和位置指示器内部采用联动三相电磁线圈。
当襟翼运动时，位置传感器将襟翼传动杆的转动转化为其内部电磁线圈的位置偏转，由于传感器线圈和指示器的线圈采用联动形式，当传感器线圈位置发生变化时，传感器和指示器的电磁线圈之间就形成了电位差。
该电位差将在两个线圈的回路之间形成电流，驱动指示器线圈也发生位置改变，当指示器的线圈位置运动到与传感器线圈位置相对应时，两个线圈之间的电位差消失，回路中的电流也随之消失，指示器的线圈停止运动。
同时指示器的线圈连接着指示器的指针，当线圈运动时，指针随之运动而指示不同的位置，从而实现指示襟翼位置的功能。
看着挺复杂，其实这里就把它们简单理解成发电机带着电动机转就行啦。
参照波音的分析：
Background
The trailing edge flap position and indication system on the 737NG consists of a pair of flap position transmitters (PN 18-1738-10/-12), a flap position indicator (PN 2061-15-1), airplane wiring, and the FSEU (PN 285A1200-1/-2).The transmitters and indicator are directly wired to each other through the FSEU. This allows the FSEU to monitor the voltages between the transmitter and indicator synchro stator connections and measure the trailing edge flap position for each wing. The FSEU then compares the difference between the left and right wing flap positions. When the difference exceeds 9 synchro degrees, a flap asymmetry shutdown occurs. This shutdown is latched by the FSEU and can only be reset when the airplane is on ground.
These flap asymmetry faults are almost never repeatable on the ground. Many operators replace the flap position transmitter (as recommended by the FIM) and return the airplane to service. Since the fault is intermittent and does not repeat after the airplane has returned to service, most operators conclude that the flap position transmitter was the faulty component.
襟翼锁死故障在地面几乎重现不了。
Status
Boeing has concluded our root cause investigation into these flap asymmetry events. Our investigation has concluded that a faulty flap position indicator can cause a flap asymmetry shutdown. In addition, the investigation found that conditions occurring within the flap position indicator synchros make the flap position indicator much more likely to cause a flap asymmetry shutdown than previously thought.
Boeing found that electrical arcing is occurring internal to the synchros between the brush and slipring of the synchro. It is not known why the electrical arcing is occurring between the brush and the slipring, however, it is thought that it may be due to airframe vibration causing the brushes to momentarily lift off the slipring creating an air gap. The electrical arcing causes erosion of the brush and increases friction between the brush and slipring. Both of these effects can result in a lagging or stuck indicator synchro that is detected by the FSEU as an erroneous flap measurement. When this condition persists long enough, the 9 synchro degree flap asymmetry margin can be exceeded resulting in a flap shutdown.
同步器上的电刷和滑环上产生了电弧，导致位置指示卡住或者滞后。
In addition, Boeing's investigation also found that increased resistance in the airplane wiring between the flap position transmitter and the FSEU can also result in a flap asymmetry shutdown. Increased resistance on the synchro stator wiring by approximately 80 ohms or more can also cause the FSEU to measure an erroneous flap position resulting in a flap shutdown. Boeing believes that 80 ohms of additional resistance can occur due to corrosion within the transmitter connectors or other exposed connectors between the transmitters and FSEU.
传感器与飞机线路阻值增大（80欧姆）也会导致襟翼锁死。
Interim Action
Boeing recommends that operators inspect and clean flap position transmitter connectors D40034, D40024, D229, and D275 in accordance with Boeing Service Letter 737-SL-24-207 on a regular basis at a convenient maintenance opportunity and following any flap asymmetry event.
Subsequent to any flap asymmetry event, Boeing recommends that operators consider replacing the flap position indicator as the first maintenance action taken. For asymmetry events that are NFF after maintenance troubleshooting, operators may consider replacing both the flap position transmitter and the flap position indicator.
建议优先更换襟翼位置指示器，如果排故没有发现问题，可以考虑襟翼位置指示器和传感器一起更换。
Final Action
Boeing is revising the FIM and AMM to provide better troubleshooting recommendations following a flap asymmetry shutdown event. These recommendations will take into account the new understanding of how the flap position indicator and wiring faults can cause flap asymmetry events to occur.
目前手册还未改版。
三、最后总结
今后遇到此类故障时，可以先检查相应插头并测量阻值。
如果故障在地面能复现，或者能被检查出来，可以脱开襟翼位置指示器表头插头后再试。
如果检查没有发现问题，也要优先考虑更换襟翼位置指示器。
完
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