Sichuan A319 at Wuxi on Sep 14th 2010, full stall condition on approach in microburst
Last Update: November 29, 2013 / 18:35:28 GMT/Zulu time
Incident Facts
Date of incident
Sep 14, 2010
Classification
Report
Airline
Sichuan Airlines
Flight number
3U-8949
Departure
Chongqing, China
Destination
Wuxi, China
Aircraft Registration
B-6054
Aircraft Type
Airbus A319
ICAO Type Designator
A319
China's Civil Aviation Authority (CAAC) released their final report via the French BEA (the report does not appear, not even in Chinese, on usual CAAC websites, that used to report aviation safety occurrences until July 2010, at which point all aviation safety reporting on CAAC websites stopped with the only exception of the final report into the crash of Henan Airlines in Yichun) concluding the probable causes of the serious incident (major aviation transport incident) were:
Findings
- The crew did not pay enough attention to the complex weather condition, and their decision-making ability was weak. The crew had made wrong decisions in the severe weather condition. Although ATC informed the pilots of the weather conditions and other planes’ diversion, the flight crew continued to launch the approach.
- The alternative plan prepared for complex weather condition was insufficient. When wind shear became obvious, pilots took no resolute action to stop the approach.
- The crew failed to respond as per manual. When the aircraft attitude was gradually deviating from norm, air speed decreased and low energy warning appeared, the pilots intervened in the AP control by choosing the speed manually instead of pushing the throttle forward as QRH2.03, leading to complex situation, including increasing attitude, low airspeed, Alpha Protection triggered and stall.
- The Crew Resource Management was a chaos. When aircraft was in complex conditions, pilots reacted out of their instinct, leading to dual side stick inputs for as long as 12s.
Cause
In accordance with article 3.13 of Civil Aircraft Incident, this is a serious air transport incident, caused by flight crews’ inappropriate decisions and handling under adverse weather conditions.
The CAAC analysed based on QAR data analysis, that the aircraft encountered straight cross winds of between 25 and 50 knots while turning final and intercepting the localizer, that within 5 seconds changed to a tail wind of about 30 knots and a vertical downdraft of 30 knots. During the encounter the angle of attack reached a maximum of 33.4 degrees nose up and 5.98 degrees nose down, the bank angle varied between 43.54 degrees right and 7.03 degrees left, the maximum rate of descent was 3924 feet per minute and the lowest indicated airspeed was 74 knots (stall speed at 99 KIAS) reaching that low within 18 seconds from 127 KIAS, the angle of attack rose from 10.2 degrees nose up to 33.4 degrees nose up in the same time. The CAAC annotated that the angle of attack prrior to the stall event had already been unusually high at 10.2 degrees probably due to the vertical downdraft already present, usual angle of attack is around 4 degrees nose up.
According to the QAR the alpha protection activated at 93 KIAS and controlled the elevators fully down for a period of 7 seconds, causing both flight augmentation computers to drop offline and causing the pitch angle to reduce from 34 to 4 degrees nose up, the angle of attack however continued to increase until reaching 32.4 degrees until finally gradually reducing and decreasing below the alpha protection limit.
The CAAC stated: "Meanwhile, Alpha Protection function was activated to make the aircraft nose down, and gradually recovered the aircraft, which demonstrated the effective protection."
At that time Alpha Floor activated accelerating the engines from 1.27 EPR at that time to TOGA within 2 seconds causing the aircraft to pitch up again and again exceeding the Alpha Protection Limit (AoA at or above 13 degrees nose up). The autopilot was automatically disconnected at that point, the stall warning activated for 6 seconds. The CAAC analysed, that the vertical acceleration (wing load) at that time was 0.8, not 1.0G, thus reducing the actual stall speeds. According to QAR the angle of attack again exceeded 23 degrees (activation of stall warning) at a speed between 93 and 81 KIAS (no further accuracy possible due to QAR sampling intervals of 1 second) leading to the conclusion that in the attitude and wing load situation of the aircraft the actual stall speed was 79 knots.
The CAAC stated: "The triggered stall warning as shown by the decoded data was between 93kt and 81kt (CAS), higher than 79kt, demonstrating that the stall warning was triggered before the aircraft stalled."
The CAAC summarized the analysis: "Under the Influence of microburst and the following windshear, the aircraft attitude changed significantly. Although the Alpha Protection function was activated before stall, it was still quite hard to effectively stop the aircraft from stalling, because the energy produced by the weather at that time had exceeded that of auto protection system."
Incident Facts
Date of incident
Sep 14, 2010
Classification
Report
Airline
Sichuan Airlines
Flight number
3U-8949
Departure
Chongqing, China
Destination
Wuxi, China
Aircraft Registration
B-6054
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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