2019年12月份，机队737NG连续发生了多起航前起动活门无法打开的故障，造成了几次不正常。
在近期的空地交流上，也就此情况与机组进行了交流。
典型案例：
某737NG飞机，鄂尔多斯航前左发启动2次不成功，起动活门打不开。人工操纵活门一次后，机组重新启动正常。飞机正常出港。后续航段运行中起动正常。
下面对这类故障做下简单的说明。
一、事件背景Three operators have reported this condition, which occurred during particularly cold periods in Europe in the past two years. Although these represent the only reports on 737NG-series airplanes, many 737-300/400/500 operators have previously reported frozen start valves. As the same start valve is used between these two 737-series airplanes, this condition is not unexpected. Ice buildup on the butterfly valve inside the start valve is the primary cause, which prevents normal opening of the valve. When the butterfly valve is cycled several times or when the start valve is manually opened, the ice usually breaks and the butterfly valve is free to rotate.
在过去两年欧洲特别寒冷的时段，三家航空公司报告了这种情况。尽管这些是737NG系列飞机上的唯一报告，但许多737-300/400/500航空公司之前报告过起动活门冻结。由于这两种737系列飞机之间使用的是相同的起动活门，这种情况并不意外。起动活门内蝶阀上的积冰是导致阀门无法正常开启的主要原因。当蝶阀循环几次或人工打开起动活门时，冰通常会破裂，蝶阀可以自由旋转。This icing condition is caused by moisture inside the pneumatic system which freezes during long exposure to cold weather. The source of the moisture is usually the engine bleed system, although this condition can also occur as a result of certain cold and wet weather conditions. During engine operation, moisture is introduced in the form of humidity or when flying through rain. As the air is subsequently heated by the compressor, it can absorb additional moisture. This moisture-laden air then travels through the engine bleed system and eventually reaches the strut, where the starter duct joins the engine bleed duct. When the engine is shut down and cools, the air in the ducts becomes saturated and condensation occurs. This condensation can form ice on the start valve and prevent normal valve operation. There are no preventative steps that can be used to prevent this ice accumulation from occurring.
在长时间暴露在寒冷天气下，气源系统会结冰，这种结冰情况是由气源系统内部的潮气引起的。潮气的来源通常是发动机引气系统，然而也可能是某些寒冷和潮湿天气条件造成的。在发动机运转过程中，水分以湿度的形式或在雨中飞行时引入。随着空气随后被压缩升温，它可以吸收额外的水分。然后，这些充满水分的空气通过发动机引气系统，最终到达支柱，在这里，起动管路与发动机引气管路相连。当发动机关车后冷却时，管道中的空气变得饱和并发生冷凝。这种冷凝会在起动活门上形成冰，从而妨碍活门正常工作。没有任何预防措施可以用来防止这种结冰的发生。There are no preventative steps that can be used to prevent this ice accumulation from occurring. However, the referenced AMM procedure provides information for operating the engine in cold weather. In regard to using the APU to heat the start valve without operating the valve; Boeing advises this practice is not effective as the APU hot air will not reach the start valve, due to the cold air trapped in the starter duct.
没有任何预防措施可以用来防止这种结冰的发生。但是，参考的AMM程序提供了在寒冷天气下操作发动机的信息。关于在不作动活门的情况下使用APU加热起动活门；波音公司建议这种做法是无效的，因为APU热空气无法到达起动活门，由于冷空气还被封在起动机管路中。
AMM 71-00-00/201：
The referenced AMM engine cold start procedures will be revised to advise that manual operation of the start valve, without pneumatic pressure applied to the valve, can cause internal binding and damage to the start valve. This damage may then lead to future decreased reliability of the valve. AMM发动机寒冷天气下起动程序里，改版增加了建议：在活门未接通气源的情况下手动操作起动活门，可能会导致起动活门内部卡阻和损坏。这种损坏可能会导致活门未来可靠性降低。737NG飞机冬季常见问题与处理
注意做好人员和机组之间联系。
重新起动几次，如果起动成功，可正常放行。注意起动电门放GRD位的时间稍微长一点，虽然起动活门没打开，但是起动电门在GRD位，APU会进入MES模式，引气压力和温度都会升高，有助于将起动活门上的冰融化。
如果起动不成功，机务可人工操控活门起动（提醒机组打开APU引气/隔离活门），待活门成功打开（全开是转90°，转约30°即可）后，机组再正常起动一次，如果活门打开正常，飞机可正常放行。否则，需要按MEL80-03保留放行。