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最近,连续发现好几起主轮舱的易碎接头漏油,导致A系统液压油量减少的事件。而且很多还是波音出厂不久的飞机。
在系统里查了一下,发现其他地方也有类似情况,在此简单总结一下。
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故障现象
地面发现A系统油量偏少,B系统正常。或者A系统隔几天就要加一次油,明显异常。
有时A系统油量少的比较厉害,达到勤务值(76%),AHM上会有报警:
检查一般能看到机身下部、靠近主起落架轮舱附近有油迹,但是增压又看不出来渗漏点。此时可能就需要检查主轮舱里的易损接头了。
检查除了要增压液压系统外,还需要插上起落架销子,将起落架手柄移动到UP位,此时很可能就会看到油从易损接头这里喷出来。
原因分析
其实易损接头漏油很早之前就有了,相关内容可参见波音1999年发布的一个FTD:
737NG-FTD-32-00014 Main Landing Gear Wheel Well Hydraulic Frangible Fitting Leaking Hydraulic Fluid
Description
Two operators reported finding Model 737-600 and -700 airplanes with hydraulic fluid residue on the underside of the fuselage near the main landing gear wheel wells.
The source of the leakage was found to be the frangible hydraulic fitting assemblies, P/N 273A2801-3.
The operators reported that the leakage was found by moving the landing gear control lever to the "UP" position with the landing gear ground lock pins installed and the "A" hydraulic system pressurized. Fluid was found spraying from either the frangible fitting or the adapter installed in the manifold body.
These components were found to be loose and were tightened to stop the leak.
Final Action
A quality check found that the fittings were being properly tightened as stated in the engineering drawing requirements.
Boeing conducted further tests on the frangible fittings and found increasing the installation torque for the MS21902J6 union to the 273A2802-3 manifold from 170 in-lbs to 215 in-lbs reduces the likelihood of the fitting becoming loose.
波音的解决措施是将接头的力矩从170磅寸增加到215磅寸,防止接头松动。并将之修订到AMM手册中。
排故建议
如果插上起落架销子后,增压A系统,发现易损接头漏油,优先更换此处的封圈:
封圈【4】【10】的件号是:NAS1612-6A(IPC 32-32-52-02-040);
接头【5】【11】的安装力矩为215 ± 10.8 磅寸;
液压管【6】和B型螺帽【7】的安装力矩是270 ±14 磅寸。
这里特别要注意的是,安装【6】、【7】、【8】时,一定要使用两个扳手,其中一个扳手要把接头【5】、【11】固定住,避免将接头处的封圈弄坏,造成后续出现漏油。
封圈损坏导致漏油 ----------------------------
附:
经常也有人这两个凸出的东西是干什么的,顺便说下易碎接头的作用。其实AMM SDS 32-32-00里就有说明。
易碎接头就是在起落架收放作动筒的收上压力油路上接了一根管到图上的位置,其上游还有一个液压保险。
当轮子损伤胎面分离,并且在收起落架时,收上刹车失效轮子还在高速旋转,轮胎碎片会将易碎接头打烂,液压油由此处漏出,收上压力从有破损轮胎的主起落架作动筒卸掉,主起落架停止收上并向放下位移动。
这样就可以阻止起落架继续收上,防止轮胎碎片进一步打坏轮舱内的部件。
随着液压油的继续流出,收上压力管路内的液压保险关闭,防止系统液压油更多的流失。
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