Two years ago, the incident report regarding the Sichuan Airlines Flight 3U8633 Airbus A319 Cockpit Windshield Crack and Blowout was officially released. All materials can be found on the China Civil Aviation Safety Information System website.

SWCAAC-SIR-2018-1_Final_Report_Appendix1Ref_12-14.pdf

SWCAAC-SIR-2018-1_Final_Report_Appendix1Ref_1-7.pdf

SWCAAC-SIR-2018-1_Final_Report_Appendix1Ref_8-10.pdf

SWCAAC-SIR-2018-1_Final_Report_Appendix1Ref_11_part1.pdf

SWCAAC-SIR-2018-1_Final_Report_Appendix1Ref_11_part2.pdf

SWCAAC-SIR-2018-1_Final_Report_MainText.pdf

A partial excerpt of the content is as follows:

The most likely cause of this incident is: The seal (weather seal or sealant silicone) of the right windshield of aircraft B-6419 was likely damaged, and a cavity existed inside the windshield. External moisture intruded and accumulated at the bottom edge of the windshield. After long-term immersion, the insulation of the power wires decreased, leading to continuous electrical arcing in a humid environment at the lower-left corner of the windshield. The local high temperature generated by the arcing caused the double-layer glass structure to crack. The windshield could not withstand the pressure differential between the cockpit and the outside, leading to its explosive separation from the fuselage.

Based on the combined test results from both the Chinese and French sides, it was found that the sealing silicone possesses the following characteristics: · After aging, the main functional group structure, glass transition temperature, expansion rate, and hardness of the sealing silicone material showed no significant changes, indicating that the sealing silicone has a certain degree of weather resistance; · During the inspection, cracking of the sealing silicone was observed, with the direction of crack propagation extending from the inside out; craze cracking was observed on the contact surface between the sealing silicone and the glass layers. · According to ISO1817, after wet treatment (immersion) with deionized water at 70°C, the tensile mechanical properties of the sealing silicone declined.

The impact of the windshield rupture on the cockpit gas environment is mainly divided into two parts: the impact on cockpit pressure and the impact on cockpit temperature. Impact on cockpit pressure: According to flight data, after the A319 windshield cracked, the cockpit suffered decompression. At 07:07:51, the cockpit pressure altitude exceeded 25,000 ft. As the aircraft initiated Descent, the cockpit pressure altitude gradually decreased, dropping below 25,000 ft at 07:09:07. Therefore, the duration during which the cockpit pressure altitude exceeded 25,000 ft was 1 minute and 15 seconds. Impact on cockpit temperature: According to CFD simulation data, during the entire Descent process, the temperature inside the cockpit fluctuated between -24°C and 8°C, with the duration spent at -24°C not exceeding 1.5 minutes.

During the entire Descent process, the wind speed at the Captain and First Officer seat positions was less than 10m/s (wind force not exceeding Level 5); the maximum wind speed inside the entire cockpit did not exceed 18m/s, equivalent to a Level 7 wind.

When the windshield of aircraft B-6419 exploded and separated, the flight Mach number was 0.76. Based on the standard atmospheric condition where the static pressure at 9800m altitude is 272.5579 hPA (derived from Table 19) and the total pressure calculation formula: Ptotal = Pstatic × (1 + 0.2M^2)^3.5 (where Ptotal is total pressure, Pstatic is static pressure, and M is flight Mach number), it was calculated that after the windshield shattered, the total pressure was approximately 399 hPA.

This pressure value is close to the pressure value at an altitude of 7200m under standard atmospheric conditions. This means that after the windshield explosion at 9800m, the cockpit pressure environment was equivalent to being statically exposed to the standard atmosphere at approximately 7200m without pressurization. Although the airflow flowing into the cockpit causes a slight disturbance to the total pressure, this local minor disturbance has little effect on the total pressure. According to the altitude sensor recording of the CPC in the DAR log after the windshield separation, the cabin altitude quickly reached 7317m (24000ft), which also confirms this conclusion.

Additionally, DAR logs show that during the flight, the total time the cabin altitude exceeded 7500m was 1 minute and 19 seconds. The maximum cabin altitude reached 26368ft (approximately 8039m) for about 4 seconds. The cabin altitude was far below the cruise altitude of 9800m.

Considering that after the glass shattered and separated, the aircraft engine bleed air system and air conditioning system were still operating normally. Due to the sudden drop in pressure and temperature inside the aircraft, the pressurization and temperature control logic would command the system to supply more hot air than before the failure to meet the pressure required by the pressurization logic and the air conditioning outlet temperature. This also contributed to a certain increase in cockpit pressure and temperature.

In summary, although the windshield separation occurred at a cruise altitude of 9800m, due to the dynamic pressure and bleed air during the flight at Mach 0.76, the cockpit pressure and temperature environment were better than the environment at a static 9800m. This is one of the reasons why the flight crew did not suffer obvious hypoxia or frostbite.

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