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LEAP 1A 发动机 自动点火失效分析 背景 LEAP 1A 经常会出现第一个自动启动循环三次点火尝试均失败的现象，重新进入第二个自动启动循环。 现象分析 LEAP 1A 点火失败时自动循环的逻辑下：LEAP 1A发动机的一个自动点火启动循环包括三个启动点火尝试： Ø 第一次尝试------正常燃油流量+单点火(回路A或B)回路 Ø 第二次尝试 增加燃油流量(7%左右)+单点火(使用与第一次尝试相同的点火)，如果尝试失败，ENG 1(2)IGN A(B)FAULT警告显示 Ø 第三次尝试 增加燃油流量(与第二次启动尝试同样燃油流量)+双点火(回路A 和 B)，如果三次都尝试失败，ENG 1(2) IGNITION FAULT或ENG 1(2)IGN A+B FAULT 警告显示 LEAP 1A 发动机第一次尝试启动成功大概需要 70-115秒(根据不同的热状态)，增一次启动尝试增加大约45秒的启动时间。 其实知道这些远远还不够，笔者也去查了AIRBUS EWIS中TFU，果然18-MAR-2019有这么一份TFU 74.00.00.096。CFM公司已经着手解决这一问题。 Applicability: All A320neo family A/C fitted with CFM LEAP-1A engines. Reference / Documentation: · TSM task Ref. 74-21-00-810-809-A / 74-21-00-810-810-A. · AMM task Ref. 74-00-00-710-803-A. · MMEL Operational Procedures 74-31-01A / 74-31-02A. Description Operators have reported cases of delayed engine light-off while performing the engine autostart procedure. The delayed light-off is associated to the triggering of ECAM message ENG x IGN A (B) FAULT and to FC ENGxD-0253-IGN1 SYS or ENGxD-0258-IGN2 SYS. During the engine autostart sequence initiated by the crew, the first and second automatic starting attempts performed by the EEC fail due to lack of EGT rise within 15 seconds of fuel ON and ignition activation. Light-off is then typically successfully achieved on the third attempt automatically performed by the EEC, with increased fuel flow and activation of both ignition systems. Although the engine eventually achieves a successful light-off, ECAM message ENG x IGN A (B) FAULT is a MMEL short-term dispatch item and requires maintenance action within 10 days. This can cause operational interruptions due to the need to invoke the relevant MMEL item. 虽然发动机最终成功点火，但ECAM会出ENG x IGN A (B) FAULT故障信息，而且这个项目是MMEL的短期项目，需要在10天内采取维护行动。这可能会导致AOG，所以需要调用相关的MMEL项目。 The issue is typically reported as intermittent and not occurring on every start attempt. However, in some cases this resulted in significant maintenance burden to replace the LRUs involved in the system, in most cases without actually solving the issue. 该问题通常被报告为间歇性的，并不是在每次启动尝试时都发生。然而，在某些情况下，这导致了替换系统中涉及的LRU而导致重大维护负担，在大多数情况下，并没有实际解决问题。 Similar issues with the engine starting performance had been reported at EIS and have been addressed by CFM by means of the EEC SW standard FCS4.0. Since the introduction of FCS4.0, the engine starting performance was significantly improved. However, Airbus and CFM have observed recently an increase in the number of IGN FAULT reports, affecting also some recent deliveries and pre-delivery aircraft. Consequence Operational limitations may be imposed in relation to this issue, notably with the aircraft placed under short-term dispatch MMEL and with ETOPS limitations in case system A is affected. Also, cases of operational interruption have been reported linked to this issue. Investigation Status For the vast majority of the cases reported to Airbus and CFM, no actual hardware fault is suspected. This is based on the following considerations: l · When maintenance has been carried out, the replacement of all the relevant LRUs (igniter plug, igniter exciter, igniter lead and in some cases the EIU) did not fix the issue. l ·The IGN X FAULT appears intermittently, with a number of successful starts reported on the same ignition system. Actual hardware faults would likely result in the engine always failing to achieve light-off when that system is used for starting. l · Cases have been reported in which the engine failed to achieve light-off under the alternate ignition system as well (when the suspect system was isolated by pulling the relevant C/B as per MMEL operational procedure). CFM launched an investigation on this issue and reviewed the manufacturing details of the affected engines with nil significant findings which could explain the phenomenon. EEC SW upgrades since FCS4.0 have been ruled out as contributors as no change to the light-off logic was introduced since then. CFM对这一问题展开了调查，并审查了受影响发动机的制造细节，但没有发现可以解释这一现象的重大发现。自从FCS4.0以来的EEC 软件升级此因素已经被排除，因为从那时起就没有引入对点火逻辑的更改。 One of the potential contributors to the issue is linked to the thermal state of the engine, notably in relation to the residual EGT at start. This is considered as a contributing factor but not the only cause of the phenomenon. 这一问题的一个潜在因素与发动机的热状态有关，尤其是与启动时剩余EGT有关。敲黑板，这就是重点。 这被认为是造成这种现象的一个因素，但不是唯一的原因。 Mitigation / Interim Plan At this time, Airbus and CFM do not recommend any specific troubleshooting or LRU replacement, as long as： l · The engine achieves light-off at the third automatic attempt. l · The IGN X FAULT tends to occur intermittently and not at every startperformed under the suspected system. Indeed, TSM tasks ref. 74-21-00-810-809-A and 74-21-00-810-810-A indicate that: “If the fault did not reoccur within the next three engine starts, then no mainten nce action is needed.” Airbus and CFM would encourage Operators to take advantage to this allowance included in the TSM. In case the fault reoccurs in all of the next three engine starts, then a test of the ignition system as per AMM ref. 74-00-00-710-803-A should be performed.If the test is successful, no further maintenance action is required Some Operators have attempted to perform a manual engine start as a mitigation. While a manual engine start activates both igniters thus introducing more energy in the combustor,there is no increase of fuel flow with this procedure. 一些运营商试图通过人工启动发动机来缓解。当人工启动发动机使用双点火，从而在燃烧室点火中引入更多的点火能量，但是此程序并没有增加燃油流量。 CFM considers that successful starts are more related to an increased fuel flow into the combustor, rather than to dual ignition. For this reason, CFM and Airbus do not consider the manual starting procedure as an effective mitigation at this point in time. CFM公司也认为，成功的启动更多地是与进入燃烧室的燃油流量增加有关，而不是与双点火有关。因此，CFM和空客并不认为手动启动程序是目前有效的缓解措施。 Engine CEOD data and DFDR raw data may be useful for deeper investigation on aircraft severely affected and with multiple reports of IGN X FAULT. Maintenance Information Please refer to TSM tasks ref. 74-21-00-810-809-A and 74-21-00-810-810-A for allowance to defer maintenance action. Repercussions on A/C Operations Please refer to MMEL Operational Procedures 74-31-01A and 74-31-02A. Permanent Solution No long-term solution has been identified for the time being. CFM are currently considering a new EEC SW upgrade (post-FCS6.0) to improve the light-off logic with an updated fuel schedule, pending the completion of the root cause investigation 目前还没有确定长期的解决办法。CFM目前正在考虑一个新的EEC软件升级(后fcs6.0)，以改进点火逻辑与更新的燃油计划，直到完成根本原因的调查 看完这份TFU，对于LEAP 1A发动机在自动启动时点火失效的点火逻辑和为什么会导致这一现象有了更深层次的学习和了解。 |
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