737NG FMC软件缺陷导致重启

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FMC重启问题，长期以来一直存在，之前也和机组做过这方面的交流。

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事件背景

某737NG飞机，巡航阶段，飞行高度10100米，FMC出现重启现象，大约15秒左右自动恢复，故障期间水平导航断开、双CDU无显示、机长一侧ND屏出现VTK故障旗。机组在MCP上选用航向选择、高度保持，监控飞机状态并核实飞机位置，故障自动恢复，机组正常飞行。

机组落地后报告双FMC空中重启。

下载FMC数据发给GE，GE分析FMC诊断数据后认为是一个偶发事件：内存崩溃导致FMC重启，不是软件或硬件故障，不需要换件。并且只有左FMC重启。



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原因分析

U10.8A、U11、U12版本FMC OPS均存在FMC重启问题，详细可参考工程通告EB-2016-B737-34-201-R。

波音也有好几个FTD说明不同版本的FMC OPS存在的问题。

U10.8A主要问题737NG-FTD-34-10010：

1. Dual FMC Restart Due to Unsent ADS Messages - See FTD 737NG-FTD-34-10009.

2. Intermittent Altitude Intervention Function

3. FMC Software Restart Due to Crossover Altitude Computation and the Speed Propagation Feature

4. Display of “FMC DISAGREE - VERTICAL” Message

5. Software Exception Due to Processing Lateral Offset

6. Software Exception Due to Hold Processing

7. Leg to Leg Transition Logic Forcing Overshoot of Final Approach Courses

8. Sluggish FMC Response During FMC ACARS See Operation Flight Crew Operations Manual (FCOM) Bulletin TBC-86 and Maintenance Tip 737-MT-34-055.

9. Impact of Arming VNAV on the Ground on the Windshear Escape Maneuver discussed in Multi Operator Message, MOM-MOM-11-0009-018 and is the subject of Flight Crew Operations Manual (FCOM) Bulletin TBC-85.

10. Nuisance ARINC FMC BITE Faults in FMC H/W P/N 10-62225-004

U11的主要问题737NG-FTD-34-15001：

1. Invalid Takeoff Speed Calculations when FMC U11 software is loaded without a fully enabled ACARS and AOC Datalink.

2. FMC Engine Out Standard Instrument Departure (E/O SID) Disarm anomaly when the FMC E/O SID option is enabled.

3. Display of VNAV INVALID-PERF message erroneously and requires re-entry of the Cost Index

4. Abeam waypoints not transferred to the off side FMC during a restart of the onside FMC

5. FMC Restart due to an exception in building an ACARS downlink.

6. Dual FMC Restart when accessing the RTE page when a lateral offset exists where waypoints have been collapsed due to offset geometry. Possible Mitigation for this condition is noted in the attachment to this FTD.

7. An incorrect speed or altitude constraint on a STAR waypoint may occur if an approach or runway is changed after selecting a STAR

8. FMC on ground software restart due to additional maintenance and post processing added in the U11 software

9. FMC Restart due to an exception related to too many FMC Prediction Blocks generated when a very long “DIRECT TO” leg with a large altitude gradient is entered in conjunction with ADS contract reports or when a ADS contract is received when there is a Hold at the end of the FMC route.

10. Display of VNAV Invalid message prior to Top of Descent.

11. Airplane Descent during VNAV after calculated Top of Descent (TOD) point

12. FMC Restarts due to Watchdog Timer when a Model A4 FMC is installed as the Primary (typically left) with a Model C1 FMC as the secondary (typically right).

13. Cross load Failures when a Model C1 FMC is installed as the Primary with a Model A4 FMC as the secondary and an Alternate Route and Lateral Offset is used.

14. Incorrect Display of Verify Takeoff Speeds message at Engine Start.

U12的主要问题737NG-FTD-34-16004：

1. DSPLY SRC message on CDS and brief CDS MAP display flicker along with flicker of Fuel Quantity Indication.

2. The U12 software introduced a condition where the FMC can load an incorrect EO SID on the RTE LEGs page creating a MOD flight plan. This can occur when on the DEPARTURE page and a standard SID is selected, followed by selecting associated runway EO SID. This can only occur if this sequence of selections occur before leaving the DEPARTURE page. If leaving the DEPARUTRE page followed by returning to the DEPARTURE page, the issue does not exist.

3. The U12 software introduced a condition where the IAN (Integrated Approach Navigation) along track distance calculations do not account for total length of any RF legs from the FAF to the MAP, but rather point to point distances. This artificially decreases the true total lateral distance. Using the same vertical angle with shorter distances causes the IAN glide path to be steeper than VNAV.

4. An operator recently reported a condition in the U12 software where an FMC restart occurred after a datalink attempted to retrieve Abeam waypoint information for an alternate plan Abeam waypoint. The condition can occur when an Abeam waypoint is created in RTE 1 and a direct to that abeam waypoint is executed and the route is copied into RTE 2. This results in the abeam waypoint to not be included into the FMC abeam database for RTE 2. Any subsequent downlink of a flight plan to RTE 2 will result in an FMC software restart.

而机队目前装这几种版本FMC OPC的飞机都有：







最新的版本是U14，当前，新引进的737NG飞机有安装U13。





当FMC选择电门在BOTH ON L或NORMAL位时，左右CDU都从左FMC得到数据；选择电门在BOTH ON R时，两个CDU才从右FMC得到数据。

所以左FMC重启后会导致双CDU瞬间黑屏，看起来像双FMC重启。

FMC重启时的现象：



最简单的方法就是哪一侧DU上出现VTK故障旗就表示哪侧的FMC重启了。

详细故障现象如下：


机组QRH：



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维护提示

当机组报告FMC重启后，我们需要查看FMC的故障代码。但是，在实际中，经常遇到维修人员说没有代码。



其实，不是没有故障代码，而是查看方法不对。

INFLT FAULTS

很多人不知道查看FMC故障代码要输入工程码300，然后按6R（右下角）行选键。



① 进入MAINT BITE INDEX页，按压FMCS行选键（1L）



② 按压INFLT FAULTS（1L）行选键查看航段中的故障



会有3页，按翻页键查看不同的LRU。

G表示当前地面阶段，1，2，3，4，5，6，7，8，9表示之前的航段。类似发动机的航段。

LRU后面的字母L(left)/R(right)/B(both)表示左FMC/右FMC/双FMC探测到了此LRU故障。

比如上图的故障：机组在微信群反映左CDU间歇性黑屏，另有机组反映之前他飞的时候空中也这样。

③ CDU键盘输入300，按6R行选键可查看故障记录：



此时如果有故障记录，会显示记录故障的航段。



比如上图，地面段和第8段有故障记录。点击对应的行选键可查看详细的故障信息：



以如上图为例，简单说明一下故障代码的意思：

第3行表明故障的部件或子系统。FMC-L，说明左FMC故障。

后面是故障状态。I=intermittent（间歇性的），S=steady（稳定存在的）。

再后面是故障发生的GMT时间，0346Z，对应北京时间是11：46。

下一行是故障描述。PRES POS LAT，当前纬度位置。

再后面是失效原因。RATE=receive rate failure，接收率失效；Parity=parity failure，奇偶校验失效；SSM=sign/status matrix failure，信号/状态矩阵失效；Reason=reasonableness failure，合理性失效。

FMC软件问题导致的重启，比较常见的故障代码就是PRES POS LAT RATE 和 PGM（program） FAULT。

SENSORS STATUS



另外的sensors状态页面也类似，只不过输入的工程码是100：



FAIL代表有故障记录，---- 代表此位置没有传感器。





详细自检操作可参考FIM 34-61 TASK 801 Flight Management Computer System BITE Procedure。

最后再提醒一点：

左右FMC互相监控。当一侧FMC重启后，查看本侧FMC是没有故障代码的，要查看另一侧FMC记录的故障代码。

完

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