From the cause of the Sichuan Airlines accident, see the importance of cleaning electrical facilities!

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On May 14, 2018, during the mission of Sichuan Airlines Flight 3U8633 from Chongqing to Lhasa, the front windshield of the right seat of the cockpit broke and fell off, the dashboard was lifted, and most of the radios failed. Captain Liu Chuanjian completely controlled the joystick manually and visually and with perseverance to carry out an emergency descent. The plane finally landed safely at Chengdu Shuangliu Airport, and all passengers landed safely and got off the plane in an orderly manner.

On June 2, 2020, the Civil Aviation Administration of China announced the accident investigation report of Sichuan Airlines Flight 3U8633: the right windshield seal (weather seal or silicone seal) of B- 6419 may be damaged, there is a cavity inside the windshield, and external water vapor penetrates and remains at the bottom edge of the windshield.

The insulation of the power lead is reduced after long-term immersion, and a continuous arc discharge in a humid environment occurs at the lower left corner of the windshield. The local high temperature generated by the arc causes the double structure glass to break. The windshield cannot withstand the differential pressure inside and outside the cockpit to burst out of the fuselage.



Another serious accident caused by electrical failure. Moisture usually contains various conductive ions, and various anions and cations dissolved in water will increase the conductivity of water and reduce the resistivity of water. Due to the extremely low temperature outside the cabin at high altitude, the front windshield usually needs electric heating to maintain its strength. Moisture on the wire insulation can reduce the surface resistivity of the wire, which can cause discharges along the outer surface of the wire. The heat effect generated by the discharge will evaporate the water and stop the discharge. As the wire is wetted again, the discharge occurs again. The temperature of the discharge arc can usually reach 5000-6000 ° C, which will melt the glass. The windshield of an aircraft is usually a double-sided structure, and water vapor will enter the cracks of the double-sided glass along the melting point, destroying its vacuum structure and causing cracks in the glass.



The atmospheric pressure gradually decreases with the height. For every 1000 meters, the air pressure drops by about 1300 Pa SCS. For an aircraft flying at an altitude of nearly 10,000 meters, the pressure difference between inside and outside is about 13000 Pa SCS, which is equivalent to pressing 13 tons of weight on a square meter of glass.

Since the aircraft is flying at a speed of 800-900 km/h, the Bernoulli effect that lifts the aircraft will further increase the pressure difference between the inside and outside of the aircraft, and eventually cause the windshield to be sucked out.



From this accident, we can see the importance of electrical cleaning. The surface of electrical components will generally absorb some conductive impurities such as dust, floating flocs, acid and alkaline gases, salts, etc. Under damp conditions, it is easy to produce discharge and cause accidents.

Insulation cleaning agent is generally required to have a density greater than 1.0 g/cm ∧ 3, which is greater than the density of water. In this way, the water gathered in the tiny gaps and holes of the electrical components can be driven out, so as to avoid the conductivity caused by the impurities dissolved in the water and cause the discharge accident.



If Sichuan Airlines Flight 3U8633 has carefully cleaned the electrical parts before takeoff, the moisture accumulated in the lower part of the windshield can be removed, and the impurities that cause conductivity can be removed at the same time, this accident can be avoided.

In any case, Sichuan Airlines flight 3U8633 is a blessing in luck. Thanks to the heroic captain Liu Chuanjian's rich driving experience and calm and decent emergency handling, a major accident involving the death of a plane was avoided.