2022年5月13日，某737飞机在执行航班时，机组反映有BAT DISCHARGE灯亮，后复位主警告灯正常。后续检查电源系统也一切正常。怀疑这可能是电瓶充电机完成充电后转TR模式放电所致。恰好波音新发布了737NG-FTD-24-22002证实了此点。下文将详细说明此FTD的内容及与波音交流的内容。

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2022年6月，有737NG飞机在完成启封出厂后首段出现备用皮托管失效的案例，由于启封工卡中有加温测试的要求，因此就此与波音做了相关讨论，看如果延长加温时间，是否有利于提前识别和发现加温的问题。波音总体分析认为是比较难捕捉。

波音认为，在正常维护条件下，无法提前确定皮托管探头的加热减少量。故障是瞬时发生的，就像灯泡故障一样，在故障点之前，性能是正常的。探头加热器执行为探头提供热量以防结冰的功能，这是加热元件的性能。为了保护加热器元件免受环境影响，有绝缘材料。绝缘材料可能会有一些退化，而不会影响探头加热器元件提供防冰的能力。加热元件的性能随着时间的推移保持正常，直至出现硬故障。硬故障是指防冰故障指示灯亮起而导致的开路或短路情况。正如FTD（737NG-FTD-34-15006）所述，电绝缘性能可能会下降，但在探头出现故障之前，这不会影响整体加热性能。加热器绝缘劣化会随着环境因素、飞行时间和飞行周期的增加而增加。新冠影响带来的封存可能会影响探头的可靠性。发动机在不拔出皮托管加热跳开关的情况下运行，这可能导致地面发热，可靠性降低。皮托管探头加热器护套材料易受腐蚀。腐蚀会导致加热器护套破裂，从而导致水分和污染物进入，从而降低加热器导线的绝缘性能。当绝缘性能下降到对加热器元件没有足够的电气保护时，加热器元件将与探头外壳短路。由于探头上有115Vac电压，加热器的电气故障会突然发生，一旦小电弧引发短路，它会迅速碳化，并在大多数情况下导致硬短路。

A2. The failure mode does not lend itself to predictive performance criteria. It is not possible to determine in advance the reduction in heating of the pitot probe under normal maintenance conditions. The failure occurs instantaneously, much like a failure of a light bulb, where the performance is nominal up to the point of failure.

The probe heater performs the function of providing heat to the probe for anti-ice purposes, this is the performance of the heating element. To protect the heater element from the environment, there are insulation materials. The insulation materials can have some degradation without impacting the ability of the probe heater element to provide anti-icing. The performance of the heating element remains nominal over time, up to the point of a hard failure. A hard failure is either an open or short circuit condition that results from the illumination of the Anti-Ice failure indication within the flight deck. As the FTD (737NG-FTD-34-15006) describes, there can be degradation of the electrical insulation properties, but this does not impact the overall heating performance until the point of probe failure.

Heater insulation degradation can increase with environmental factors, flight hours, and flight cycles. Storage during the COVID-19 pandemic can affect probe reliability. Engine runs without pulling Pitot heater circuit breakers, which can result in heating on the ground with decreased reliability. The Pitot probe heater sheath material is susceptible to corrosion. Corrosion causes a breach in the heater sheath which allows ingress of moisture and contaminants, degrading the heater wire insulation. When the insulation is degraded to the point that there is not sufficient electrical protection for the heater element, the heater element will short circuit to the case of the probe. The electrical failure of the heater occurs abruptly since there is 115Vac across the probe, once a short circuit is initiated by a small electrical arc, it quickly carbonizes and results in a hard short in most cases.