Sichuan A319 near Chengdu on May 14th 2018, burst windshield
Last Update: June 3, 2020 / 16:21:15 GMT/Zulu time
Incident Facts
Date of incident
May 14, 2018
Classification
Accident
Airline
Sichuan Airlines
Flight number
3U-8633
Departure
Chongqing, China
Destination
Lhasa, China
Aircraft Registration
B-6419
Aircraft Type
Airbus A319
ICAO Type Designator
A319
China's CAAC reported the first officer received a waist sprain and scratches when the right hand windshield shattered and separated. A member of the cabin crew received injuries, too. The occurrence is being investigated.
The airline reported a mechanical failure. The captain remained unharmed, the first officer received skin abrasions, a member of the cabin crew a waist injury.
The airline citing the CAAC Southwest Regional Administration subsequently released an event bulletin summarizing preliminary investigation results suggesting, that the aircraft was enroute at 9800 meters at 0.74-0.75 mach when the right hand windshield developed cracks, the crew received an ECAM message regarding the windshield heating soon followed by the windshield bursting. The first officer and a flight attendant received minor injuries (scratches). The flight crew applied the related standard procedures (emergency descent), the passenger oxygen masks were released. The flight crew was unable to establish communication with ATC due to the noise in the cockpit and thus signalled the emergency via the transponder. The windshield was still the original one, the aircraft had accumulated 19,912 flight hours in 12,920 flight cycles, no issues were outstanding on the day of the occurrence. The last C-check was on Mar 9th 2017, the last A-check on Apr 12th 2018. No windshield fault messages were recorded during the last 15 days. The investigation is continuing.
On May 17th 2018 China's AIB reported the aircraft was enroute at 9800 meters when the entire right hand windscreen fell out of the aircraft damaging the Flight Control Unit (FCU) and causing the loss of cabin pressure as result. The passenger oxygen masks were released, the crew declared Mayday via the transponder and diverted to Chengdu. After landing tyres #3 and #4 (both right hand main tyres) burst. There were minor injuries, the level of damage to the aircraft is being assessed. The occurrence was rated a serious incident and is being investigated by China's AIB.
On Jun 2nd 2020 China's CAAC released their final report in Chinese only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a Chinese only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).
The report concludes the probable cause of the accident was:
The seal of the right hand windshield of B-6419 became damaged, cavities inside the windshield permitted moisture to accumulate at the bottom edge of the windshield. Due to long term immersion the windhsield heating's power wires' insulation low but continuous arcing in a humid environment occurred. The temperatures caused by arcing caused the double glass layers to fracture, the windshield could no longer withstand the pressure difference between outside and inside pressure and burst.
The CAAC reported the aircraft departed with 119 passengers, a captain (46, ATPL and instructor rating, 11,454 hours total, 9,254 hours on type) in the left hand seat, a second captain (34, ATPL and instructor rating, 8,789 hours total, 6,708 hours on type) in the observer seat and a first officer (27, CPL, 2,801 hours total, 1,180 hours on type) in the right hand seat, 5 cabin crew and 1 security officer. The aircraft had reached 9800 meters altitude (FL321), the cabin altitude was 6,272 feet, when the crew began discussing that the right hand windshield had developed a mesh of cracks, at the same time a "ANTI ICE R WINDSHIELD" message appeared on the ECAM. The right hand windshield heating was switched off. 3 seconds later a bang was heard, the captain took control of the aircraft, another 8 seconds later the crew decided to divert to Chengdu and requested to descend to 8400 meters (FL275). With the pressure differential at 7.886 psi the aircraft began to descend. 39 seconds after the ANTI ICE R WINDSHIELD message a dull sound is heard on the CVR followed by continuous noise, DC Bus 1 and DC Bus 2 went offline, the load of the right hand engine driven generator fell to zero, the heating of left windshield as well as left and right side windows failed, autobrakes fail, FMGS #2 disconnected, SEC2 and SEC3 malfunctioned, #1, #2 and #5 spoilers failed, the autopilot disconnects, the aircraft begins to roll left and right, 2 seconds after the autopilot autothrust disconnects. Descending through FL318 the cabin altitude had increased to 24,320 feet and the pressure differential had reduced to 0.922 psi. An ECAM altitude warning activated, the ECAM electrical page popped up, ELAC1 roll channel failed (and indicates failed until end of flight), the aircraft reaches a maximum of 51 degrees left bank. Descending through FL315 the cabin altitude reaches its peak at 26,368 feet, ELAC2 both roll and pitch channels are disabled, pitch control enters "standby".
In the following 9 minutes ATC called the flight repeatedly without receiving a response.
Several dual control warnings are recorded on the FDR, the aircraft descends at 10,729 feet per minute and reached 349 KIAS. The rate of descent decreases, around FL240 the rate of descent reduces to below 100 fpm, the aircraft levels off at 23600 feet. For the first time the first officer appears to have donned his oxygen mask according to the CVR recordings. The second captain uses his electronic flight bag to review aeronautical charts, the FMGS gets reprogrammed for the diversion to Chengdu. About 9.5 minutes after the onset the aircraft continues the descent below 23,600 feet. ATC still not receiving a response from the crew blindly radioes a hand off to Chengdu's approach frequency. The crew finally declares Mayday and reports loss of cabin pressure while descending through 6000 meters (FL197), was cleared to descend to 3600 meters without the crew reading back the clearance.
20 minutes after the onset the cabin altitude reduces to below 10,000 feet again, the crew sets flaps 1, lowers the gear and sets flaps 3 for landing, the cabin altitude descends through 8900 feet, the crew attempts to turn the APU on (which however fails due to power failure), the crew announced (blindly transmitting) they were turning left to land on runway 02R, approach control clears the flight to land on runway 02R RVR greater than 2000 meters, winds from 250 degrees at 4 knots.
30 minutes after the onset the aircraft touched down on runway 02R at 156 knots over ground and stopped on the runway. The crew now contacted tower, reported they had injuries on board and could not taxi by themselves. The first officer and a flight attendant received minor injuries. Main wheels #3 and #4 lost pressure after landing. The FCU was bent aside, the 130VU panel was completely lost from the aircraft and was later recovered near Ya'an City, Baoxing County, Sichuan province, about 60nm southwest of Chengdu.
The CAAC analysed that following the burst of the windshield 17 (seventeen) circuit breakers on the 120VU panel popped causing multiple system failures including the DC Bus Bar failure. Due to the popped circuit breakers DC Bus 1 can not get power from AC Bus 1, DC Bus 1 and DC Bus 2 are powered off, and because both DC Bus 1 and DC Bus 2 are powered off, the DC BAT Bus DC Bus Bar is broken and not supplied.
The CAAC analysed that immediately following the appearance of the first cracks the first officer reached out for his electronic flight bag to read the relevant checklists, the captain in the left hand seat touched the inside of the windshield and determined the inner pane was fractured, requested and initiated a descent and a diversion to Chengdu. While the first officer was executing the checklist procedures the windshield failed completely and separated causing an explosive decompression, the first officer was sucked out of his seat in the rushing airflow and impacts cockpit components including the side stick involuntarily. The captain assumed control operating his side stick with the left hand and at the same time attempting to don his oxygen mask, which near the left back side of his body, the aircraft shakes violently, his focus is to control the aircraft hence he fails to retrieve his oxygen mask with the right hand. In the first 65 seconds after the windshield burst the aircraft maintained 0.76 mach and a sink rate of about 3000 fpm, then increased the descend reaching 10700 fpm and 349 KIAS in the descent, 132 seconds after the windshield burst the aircraft reached FL237.
The captain did not use the speed brakes during the descent, the state of flight was controlled and the availability of the spoilers was unclear with the many system faults. At 7200 meters the captain levelled the aircraft off, the speed gradually reduced to 250 KIAS. After maintaining 7200 meters for about 5 minutes the captain initiated the approach to Chengdu and continued the descent.
The crew knew ILS runway 02L at Chengdu was out of service, therefore transmitted into the blind they were going to land on runway 02R. The aircraft was exceeding the maximum landing weight, the crew therefore performed the related checklist.
The report praised the crew: "In summary, the crew controlled the flight status of the aircraft, reporting the emergency to ATC, keeping the aircraft above a safe altitude, etc., performing all key operations in line with company manual requirements."
The CAAC analysed the cockpit resource management stating that initially the captain responded to the emergency by himself only and initiated an emergency descent. Subsequently the first officer was able to return into his seat, the second captain entered the cockpit. Although no verbal communication between the crew members was possible, they communicated through gestures, the first officer set the squawk to the emergency code after returning into his seat, the second captain reminded the captain to don his oxygen masks (which however was never donned, the captain was still not wearing his mask after landing) and indicated that the conditions in the cabin were normal. Using the navigation charts on the EFB the crew tracked safe altitudes. During the descent the hand held microphone was used to declare Mayday and advise ATC of the aircraft condition and crew intent. The second captain patted the shoulders of both captain and first officer to encourage them and rubbed shoulders and arms of both captain and first officer to ease discomfort caused by the cold. Although the crew transmitted the aircraft status and their intentions to ATC, they never reported the key information that the windshield had burst in conditions of hypoxia, freezing temperatures, strong wind and high noise level.
The report praised the crew again: "During the incident handling the crew demonstrated strong CRM capability."
The CAAC analysed that survival factors included the explosive decompression, hypoxia, low temperatures, high wind speed, high noise as well as the seat belts which restrained the flight crew and protected the safety of the flight crew. The seat belt of the first officer secured his lower body in the cockpit permitting him to return into his seat. A simulation showed that the upper body of the first officer was temporarily sucked out of the windshield. Cabin, flight attendants and passenger, although also exposed to environmental conditions, were less exposed.
The explosive decompression causes sudden expansion and separation of dissolved gasses in human body fluids to form bubbles and cause tissue damage. Both captains reported they did not feel their bodies after the loss of cabin pressure. The first officer reported pain in his left arm after colliding with hard objects such as instrument panels in the cockpit. He was later diagnosed with skin contusion of his left arm in hospital. Audiometric examination showed both captain and first officer had reduced hearing with no impact to the hearing of the second captain, the first officer was subsequently diagnosed with "high frequency mild sensorineural deafness".
While the captain remained without oxygen masks from the burst of windshield to landing, the first officer was able to don his oxygen masks about 3 minutes 12 seconds. Both reported never losing conscience, the flight data confirm they performed continuous and correct flight maneouvers. There is no evidence that any of the flight crew suffered a decline in understanding, analysis and judgement. It thus can be determined, that neither captain nor first officer became (partially) incapacitated.
The time of useful conscience is largely determined by genetic factors determining the amount of hemoglobin available and oxygen consumption rate. Objectively, both captain and first officer were exposed to hypoxia, due to the rapid descent however neither of them exceeded their respective effective time of consciousness.
The temperatures in the cockpit following the burst windshield were between -24 degrees Centigrade and +8 degrees C. The EFB (iPad)'s operating temperature was between 0C and 35C. The humans, with their clothing, at the ambient temperature and wind speeds in the cockpit were exposed to -10C, which the body can tolerate for 11 minutes. With the rapid descent the temperatures rose. Thus neither humans received frostbites nor did the iPad fail.
The CAAC also provided lengthy and highly technical analysis of the failure of the windshield and its causes as well as the regulations governing the windshield, the ingress of humidity etc., which however became too technical for this translator to feel sufficiently confident about the understanding of this analysis.
On Jun 3rd 2020 our source made us aware of two additional important points contained in the report (that this translater had not understood):
The tripping of the 17 circuit breakers happened as result of a safety feature of the cockpit door. During a rapid decompression the cockpit door will automatically unlock and open in order to prevent a pressure differential between cockpit and cabin. The design however did not consider the force and impact the door can produce when it impacts the 120VU panel in such a decompression.
The captain was unable to reach his oxygen mask with his right hand due to the shoulder harness already secured and the mask too far away for this scenario. The captain would either have needed to stop controlling the aircraft for some brief time while fetching the mask with his left hand, or unfasten his shoulder harness - however, the first officer at this time was not fully in his seat, still climbing back, and due to his injuries the first officer was deemed incapacitated, the shoulder harness of the only remaining pilot thus had to remain secured.
Safety recommendations were issued to Airbus, EASA, CAAC and the operators. As an immediate safety action the AOM was updated to strengthen the procedures, for example upon a windshield crack immediately fasten the shoulder straps, in case the inner layer is fractured immediately don the oxygen masks.
Incident Facts
Date of incident
May 14, 2018
Classification
Accident
Airline
Sichuan Airlines
Flight number
3U-8633
Departure
Chongqing, China
Destination
Lhasa, China
Aircraft Registration
B-6419
Aircraft Type
Airbus A319
ICAO Type Designator
A319
This article is published under license from Avherald.com. © of text by Avherald.com.
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