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其实同样的内容老兵新传已经发过了：
737NG飞机，偶尔会出现航前APU启动好后蓝色的MAINT灯亮，同时在维护历史信息里有LOQ（低滑油量49-91227）的信息：
但是此时如果去检查APU的滑油量的话，又会发现APU的滑油量其实是不少的，不需要加油：
此时再次启动APU，就会一切正常，APU维护灯也会熄灭。
这是为什么呢?
737NG-FTD-49-13001 Nuisance Maintenance Fault on 737NG aircraft with the P/N 70720860-1 Commercial Common Controller
Description Nuisance maintenance faults have been reported on 737NG aircraft which have the 131-9B APU using the new P/N 70720860-1 ECU (sometimes referred to as the Commercial Common Controller or CCC).
一些飞机安装了新件号的ECU(P/N:70720860-1)。新ECU又被称为CCC。在使用过程中，用户报告了新ECU可能产生的一些错误信息。
New APU ECU Software Part Number (P/N) 4919-TUS-A52-00 (Boeing Specification P/N S351A401-2007) was incorporated into production on Airplane Line Number 5326, 19-MAR-2015, to fix issues with the current APU ECU Software, P/N 491A-TUS-A51-00 (Boeing Specification P/N S351A401-2005). However, after discovering a non-compliance in the new software (P/N) 4919-TUS-A52-00, MOM-MOM-15-0364-01B was issued to implement a stop and reversal back to the current software.
针对这些问题，波音之前发布了新的ECU软件，旨在解决上述问题，但无法满足要求，停止了升级又恢复到之前的软件版本。
Background Honeywell identified four issues associated with the CCC. Three of the issues are listed below with the fourth issue in the Status Section:
1. Nuisance Maintenance message in the CCC: The Legacy/Old (P/N 2118966-222) ECU (with software P/N 491A-TUS-A04-00 or P/N 491B-TUS-A05-00) is checked continuously for an over current in the indicator circuit.
The new CCC (P/N 70720860-1 with software P/N 491A-TUS-A51-00) no longer checks for over currents on the indicators. It now checks for open circuits and short circuits because of the difference in hardware in the CCC. Open circuits can only be detected when the indicator is not being commanded to illuminate, and short circuits can only be detected when the indicator is being commanded to illuminate. Maintenance Fault 49-72207 in the CCC is now an indication that there is either a short or an open in this circuit.
Boeing duplicated the problem during indicator lamp press-to-test mode. With the CCC powered on (APU running or not) and the CDU turned to the APU maintenance fault page, press-to-test the Blue maintenance light by either: 1) Pressing the blue maintenance Light 2) Pressing the master light press-to-test
A maintenance fault, 49-72207 may register. As soon as the press to test is released, the fault should clear, the CDU page will indicate that the fault has cleared and the fault will go into APU maintenance fault history.
Preliminary review of the circuits and reports from the Boeing flight line indicate that there could be other nuisance maintenance fault indications. 49-72205 Fault indicator output voltage is out of limit 49-72206 LOP indicator output voltage is out of limit 49-72207 (Current fault) 49-72208 Over-speed indicator output voltage is out of limit 49-72209 Ready to load indicator output voltage is out of limit
虚假的故障代码（从49-72205至49-72209）。新版FIM中已添加注释，新ECU的故障信息（从49-72205至49-72209）为虚假故障信息，无需维护工作。
The Boeing flight line test did not demonstrate any of the additional faults indicated. However, initial circuit review indicated that they could happen.
2. Blue Maintenance light comes while APU is running.
APU运转过程中蓝色维护灯亮 关断APU时，P5板电瓶电门关闭过早，而没有按照正常程序让执行APU冷却循环，可能产生内部错误，会导致下次APU起动时，蓝色维护灯点亮。
This condition only occurs under specific circumstance which begins with the way the APU is shut down one cycle before the indication occurs. Normal shutdown is to turn the APU switch to off and allow the APU to cool down prior to shut down. If the APU is shut down with the APU battery switches instead of following the procedure in the AMM (which allows for a cool-down prior to shut down), the APU inlet door remains open for the next APU start. At the next APU start, if the APU inlet door is open, the logic in the CCC software allows the LOQ to remain active while the APU is running. Oil levels in the gearbox drop below the LOQ switch activation point during APU operation which results in an LOQ indication even though the oil level is full.
关闭APU时，电瓶电门关闭过早：在APU完成cool down循环前，关闭了电瓶电门，APU进气门在开位，由于ECU上电自检逻辑，航前起动APU后维护灯可能会被点亮，即使滑油量是满的。
3. The APU IDEN/CONFIG page displays incorrect CCC hardware part number (70720860-2 instead of the correct P/N 70720860-1).
CDU的APU 识别/构型页面显示了错误的ECU PN（显示为70720860-2，正确件号为70720860-1）。
Status Honeywell investigation found a fourth operational mode that can cause the MAINT light to illuminate. This has a similar impact as item 2 above.
According to Honeywell, using the battery switch to shutdown the APU and prematurely terminate the cool down cycle would cause the CCC Mode logic to become out of sync. Then on the subsequent start attempt, the MAINT light would likely illuminate due to false LOQ signal.
The current CCC has a control logic that monitors APU door-failed-to-open signal during APU idle or during CCC control initialization mode. During an APU start, the CCC goes through a brief initialization-diagnostic test. If the door is sluggish due to contamination, the CCC will abort the start with a door fault. This level of door signal monitoring by the CCC is unnecessary. This software upgrade will remove the logic that monitors the APU door open signal during CCC Control Initialization mode and change that to allow the start cycle to be acceptable if the door can open fully within 30 seconds.
737NG-FTD-49-16001 provides closure information on the newly release ECU software Part Number 4918-TUS-A53-00.
Interim Action The following are interim actions if Honeywell Service Bulletin has not been implemented:
- For nuisance maintenance messages in CCC: A note was added in the APU BITE procedure to inform operators that Fault 49-72205 through 49-72209 are nuisance indications and no maintenance action is required. The change was reflected in Boeing FIM 49-60 task 801 and AMM task 49-61-00-700-801 in Feb 15, 2013.
- For Blue MAINT light illumination while APU is running: Start, operate and shutdown the APU per the AMM procedure. Allow the APU to complete the cool down cycle before turning off DC power. As an alternative, operators have the option to deactivate the MAINT light illumination for low oil quantity (LOQ) indication by following the deactivation procedure in AMM 49-61-00, page block 201, titled Low Oil Quantity BITE Deactivation. For APUs with Starter/Generators effected by Honeywell Service Bulletin 131-49-8122 (Inspect the Starter/Generator, PN 28B545-7 and -9, and Rework as Necessary), it is recommended that the MAINT light illumination not be deactivated, until it is confirmed that a conforming Starter/Generator is installed. A Starter/Generator having a non-conforming stator housing may develop cracks, leading to oil leaks, which could result in a true low oil quantity condition for the APU.
Final Action Honeywell to develop and release a newer software to solve the current issues with this ECU/CCC software. Estimated completion date is Q4 of 2016.
目前波音已经推出了新的ECU软件：4918-TUS-A53-00，详细情况可参见737NG-FTD-49-16001，在2016年11月17日 L/N 6165的飞机上使用。各公司应该很快会下发指令升级软件。
最后提醒
737NG APU维护灯亮的原因有两个： 滑油量低或者传感器故障 起动机二极管短路（一般故障灯也会亮）
个人建议： 维护灯亮后首先要读取APU的故障代码，注意当前状态和维护历史和故障历史都要看。
如果查看故障代码不是起动机二极管，重新起动APU，如果APU维护灯灭，说明是上次APU关闭时电瓶断电过早导致的，并在APU自检页面查看滑油量指示决定后续是否需要加滑油。
“ ADD level first shows when the APU has approximately 60 hours of APU operation at normal oil use rate until the APU MAINT light comes on. At the maximum oil consumption rate, there is approximately 3 hours of APU operation from ADD until the APU MAINT light comes on. ”
如果确实是APU滑油量低导致的APU维护灯亮，暂时并不会影响APU运行，可后续安排添加滑油：
“ The low oil quantity (LOQ) maintenance light will come on when there is enough oil in the APU for 30-50 hours of operation at the maximum oil consumption rate before the APU will shutdown because of low oil pressure. ”
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