737新型机身过热探测控制器

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航前在起动APU前，我们需要完成火警测试，此时飞机如果只接通了电瓶电源，OVHT/FIRE测试时，火警面板上WHEEL WELL灯是不亮的。

我们都知道，这是因为轮舱火警探测模块是由115V交流电供电的。

↑ 115V转换汇流条2，经过P6-2 A19跳开关，到D742 PIN 7，给过热探测组件M237的轮舱监控电路供电，变压后输出到轮舱过热探测器M270

但是近期，很多小伙伴都跟我反映，在一些737NG上，只有电瓶电源，进行发动机火警OVHT/FIRE测试时，火警面板上WHEEL WELL灯也能亮。

这是为什么呢？

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查看我们的AMM SDS 26章，可以发现，新增加了一种件号475928-01的控制器（之前的旧件号是35008-307）▼

是不是这个原因造成的呢？当前的737NG AMM/SSM手册还真看不出来。

但是在737-SL-26-061，厂家有详细的说明：

感兴趣的可以看看这份SL，写的很详细。

SUGGESTED OPERATOR ACTION:

Operators needing to replace a CODM can purchase the latest Kidde configuration, reference b) CODM via Boeing Spares.

The nomenclature corresponding to the BIT CODEs for the reference b) CDOM when installed on a 737NG airplane will show different FAULT DESC/FAULT MESSAGEs. Refer to the reference e) AMM procedure for a full description and to the reference f) FIM for troubleshooting instructions.

新件号475928-01的控制器显示的故障信息会更详细，从FIM里也能看出来▼

之前的控制器显示的是数字代码，而新的控制器显示是描述信息。

↑ 35008-307

↑ 475928-01

Until the reference d) FCOMs are updated, Boeing offers the following guidance to help avoid confusion and operational delay:

For 737NG airplanes with the new reference b) CODM on 28VDC power only, the ‘WHEEL WELL’ light will illuminate during the OVHT/FIRE test. This is an expected normal behavior with the reference b) CODM installed as the single fire loop (Loop A) in the wheel well is powered by 28VDC.

新控制器安装到737NG上时，轮舱过热探测只使用了控制器的单环路-A环路，由28V电瓶直流电供电。

For 737MAX airplanes with the new reference b) CODM on 28VDC power only, the ‘WHEEL WELL’ light may illuminate during OVHT/FIRE test. This is an expected normal behavior with the new reference b) CODM installed since the 737MAX is equipped with two detection loops installed in the wheel well with “AND” logic. Loop A is powered by 28VDC and Loop B is powered by 115VAC.

• Note: There is a software timer embedded in the new reference b) CODM that correlates to 115VAC power loss. Depending on how quickly the OVHT/FIRE test is conducted after 115VAC is removed, or starting from a cold dark (unpowered) airplane will affect the illumination of the ‘WHEEL WELL’ light while the new reference b) CODM is detecting the power loss or booting from a cold start.
  
  

737MAX轮舱过热探测有两个「与」逻辑的探测环路，A环路由28V直流供电，B环路由115V交流供电。轮舱也有两个过热探测器：A环路是M270，B环路是M3068。

During OVHT/FIRE TEST using 28VDC power only in reference d) Supplementary Procedure SP 6, Boeing suggests disregarding the status of the ‘WHEEL WELL’ light and confirmation of ‘115VAC FAIL’ on the front panel of the reference b) CODM.

↑ 在机组操作手册第一部SP6.2中，也已经增加了相应的备注。

Operators should continue to utilize the current Wheel Well Fire Warning System test when both 28VDC and 115VAC are present, as documented at the end of the reference d) “Electrical Power Up” Supplementary Procedure; and the Overheat and Fire Protection Panel check as documented in the normal procedure portion of the FCOM, to verify full functionality of the wheel well fire detection system.

最后提醒一下：在737NG上，件号475928-01与35008-307是可完全互换的。但737MAX上不能使用35008-307。

完

推荐阅读：

​737NG学习系列 ATA 26：翼身和主轮舱过热系统

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薛定谔的貓

昨天刚遇到过一个件号：475928-01的组件，今天就看到这了这篇文章，学到了