与发动机燃油系统堵塞相关的有以下几个警告：
ENG 1+2 FUEL HEAT EXCHANGER IN BYPASS -FUEL CONTAMINATED
ENG 1(2) FUEL HEAT EXCHANGER IN BYPASS -FUEL CONTAMINATED
ENG 1+2 FUEL FILTER CLOGGED
ENG 1(2) FUEL FILTER CLOGGED
ENG 1(2) FUEL FILTER IN BYPASS
ENG 1+2 FUEL FILTER IN BYPASS
最开始咨询空客的问题是关于为什么 ENG 1(2) FUEL FILTER CLOGGED 只会在低压油滤堵塞，且另一台发动机出现 ENG 2(1) FAIL 时才会触发。在后续的回复中，逐渐对燃油系统污染和堵塞有了更深一步的了解，所以本文就对此进行了一些总结。
一、直接看结论：
1 低压油滤堵塞会造成的 DISPATCH 信息以及 ECAM 警告按照严重程序从 LEVEL 1-5（5最严重）：
2 燃油污染同时还会影响其他系统，比如 Fuel/Oil Heat Exchanger（FOHE）。所有警告出现的顺序可能会是：
二、详细说明：
燃油首先经过 FOHE，所以如果被污染，会先引起 FOHE 的警告。其中单侧的警告只在另一发失效的情况下触发。其实对比就会发现， ENG 1(2) FUEL HEAT EXCHANGER IN BYPASS -FUEL CONTAMINATED 和 ENG 1+2 FUEL HEAT EXCHANGER IN BYPASS -FUEL CONTAMINATED 的程序是完全一样的。
然后燃油会经过 LP FILTER，就会有一系列可能出现的放行信息和 ECAM 警告。相比 HEAT EXCHANGER，这里就有另一种警告，ENG 1+2 FUEL FILTER CLOGGED 和 ENG 1(2) FUEL FILTER CLOGGED，同样，单侧警告只在另一发失效的情况下触发，而程序完全一样。在 triggering condition 中有句话 “This is the intermediary clogging threshold of the LP fuel filter.” 所谓“intermediary clogging threshold” 就是中等程度堵塞的情况下会触发，因为此时燃油还是会经过 FILTER，不是走 BYPASS。而如果堵得在严重一些必须走 BYPASS 了，才会触发最严重的的 ENG 1(2) FUEL FILTER IN BYPASS 和 ENG 1+2 FUEL FILTER IN BYPASS 警告。
有意思的是，对比上述所有警告，不管是 FOHE 还是 FILTER的，程序基本都一样，都是要求关闭燃油交输和中央油箱泵，严重的情况就再有一个关闭自动推力。如果一个接一个触发，那基本上在 FOHE 堵塞时，该做的就都做了。空客解释说，其实在系统层面，油滤堵塞的问题不大，因为最终都会走 BYPASS。而如果遇到假警告或者 BYPASS 故障，机组也无法直接做什么来解决问题。所以机组能做的就只有尽早避免交输供油导致更严重的堵塞，仅此而已。
再回到最早咨询空客的那个问题：为什么 ENG 1(2) FUEL FILTER CLOGGED 只会在低压油滤堵塞，且另一台发动机出现 ENG 2(1) FAIL 时才会触发？虽然空客没有直接回答这个问题，但从上面提到的程序内容的高度相似甚至相同，以及空客对油滤堵塞的说明来看，既然程序完全一样，就没必要设置两个了。当然，会发现 ENG 1(2) FUEL FILTER IN BYPASS 和 ENG 1+2 FUEL FILTER IN BYPASS 确实在没有 ENG 2(1) FAIL 警告的情况都可以触发的，但其实 ENG 1(2) FUEL FILTER IN BYPASS 的程序就只有关闭交输供油，实际上在之前的警告中就已经关了，所以这个警告基本上可以算是一个提醒，个人觉得也是可有可无吧。
在这之后燃油污染还会引起的问题在 ENG 1+2 FUEL HEAT EXCHANGER IN BYPASS -FUEL CONTAMINATED 的程序说明中有提到：
三、具体请参考 TechRequest 原文：
Q: ENG 1(2) FUEL FILTER CLOGGED
Why this alert is triggered only when the ENG 2(1) FAIL ECAM alert is triggered on the opposite engine? If now only one eng fuel filter is clogged because of corresponding wing tank contamination without eng failure, according to current triggering condition, neither of ENG 1(2) FUEL FILTER CLOGGED and ENG 1+2 FUEL FILTER CLOGGED will be triggered. Is it resonable?
A:
We would like to confirm that as mentioned in your message (and as described in the FCOM PRO-ABN-ENG-7331W150 Triggering Conditions), the alert ENG 1(2) FUEL FILTER CLOGGED is displayed to the crew only when another failure is detected on the opposite engine side (ENG 2(1) FAIL ECAM).
As per design, if a contamination starts to clog the Low Pressure (LP) fuel filter, the first level of the LP fuel filter monitoring function will trig the DM ENG 1(2) FUEL FILTER PARTLY CLOGGED (dispatch allowed for 30 flight hours).
In the case of a more severe contamination, the second level of the LP fuel filter monitoring will then lead the EEC to emit the message ENG 1(2) FUEL FILTER CLOGGED on DISPATCH page to indicate an impending Low Pressure fuel filter blockage and that the associated LP fuel bypass valve is not open.
Whereas this situation requests maintenance before next flight (DM ENG 1(2) FUEL FILTER CLOGGED is NO GO), it does not require immediate action from the crew in flight.
Indeed, at system level, a fuel filter clogged is not supposed to have any effect since the fuel flow should ultimately go through the bypass valve (third threshold of the LP fuel filter monitoring reported through the ENG 1(2) FUEL FILTER IN BYPASS alert).
It must then be noted that:
- In the case of a spurious alert or a failed bypass, nothing can be directly done by the crew to recover the issue and no action is required in flight,
- If the contamination is limited to one engine, the ECAM actions associated with alert ENG 1(2) FUEL FILTER IN BYPASS will be applicable (see answer 3),
- The ENG 1(2) FUEL FILTER CLOGGED alert will be displayed on the WD with a LAND ANSA procedure when another failure is detected on the opposite engine side to request the crew to set to OFF both the crossfeed valves and the center tank pumps. The purpose of the procedure is to limit the impact of a cross contamination on the remaining engine.
Q_2:
Thanks for explanation of triggering sequence of those alert. As the level of contamination, the notification to crew is as follow:
A2_2:
We confirm that the content of the table is correct.
However, please note that the “most severe contamination” is indicated by the ENG 1+2 FUEL FILTER IN BYPASS message.
Indeed, as mentioned in the annunciations section of the FCOM/PRO/ABN, the ENG 1+2 FUEL FILTER CLOGGED alert is displayed when both engines are contaminated and the intermediary clogging threshold is reached. Note that at this stage, the LP fuel filter bypass are still closed.
If the contamination continues to progress and the bypass valves on both engines finally open, the ENG 1+2 FUEL FILTER IN BYPASS alert will then be displayed.
As highlighted in the table, both ECAM procedures require LAND ANSA with Crossfeed valves and Center fuel tank set to OFF. In the most advanced scenario (i.e. ENG 1+2 FUEL FILTER IN BYPASS), it is then requested to the crew to set the A/THR to OFF and to avoid rapid thrust changes in order to prevent both engines from stall.