1/ Russian investigators believe the high-speed crash of an Su-30SM fighter jet in Irkutsk on 23 October may have been due to the aircraft's oxygen system malfunctioning, causing the two crew members to suffer a fatal case of hypoxia. Thread ⬇️
https://twitter.com/i/status/1584139584383774721/video/1
2/ Media reports say that the Eastern Interregional Investigation Department for Transport of the Investigative Committee of the Russian Federation has opened a criminal case for "violation of the rules of traffic safety and operation of air transport" based on early findings.
3/ According to the investigators, the aircraft's oxygen system most likely malfunctioned, causing a lack of oxygen, an excess of it, or accidental contamination of the oxygen with nitrogen. This could have caused the two-man crew to both lose consciousness at the same time.
4/ The crew had been carrying out final acceptance tests on the new Su-30SM at an altitude of 9,000 m. However, comunications with the pilots, Maxim Konyushin and Viktor Kryukov, were lost at 17:50 local time. Subsequent attempts to contact them by radio were unsuccessful.
5/ The aircraft was in automatic control mode, so the autopilot carried out the planned tests before returning the aircraft to the approach to the Irkutsk aircraft plant's airfield. At this point, the crew should have taken over, reduced speed and started the glide path. 
6/ Instead, the autopilot sent the jet into a long circle over the outskirts of Irkutsk at about 800-900 km/h and an altitude of about 600m. Sergey Mikhailyuk, the chief Sukhoi test pilot, used another aircraft to try to see what was wrong.
7/ Mikhailyuk found that the Su-30SM itself was in good condition, but "both of its pilots were sitting limply in their chairs, their heads bowed." He could not intervene. The aircraft circled for 30 minutes before its final plunge at 18:19, crashing into a house.
8/ The reason for the aircraft's sudden fall is not yet known, but it's thought that one of the pilots may have slumped forward onto the controls, perhaps after having earlier loosened his harness while trying to resolve the oxygen fault. There were no casualties on the ground.
9/ The pilots may already have been dead of hypoxia at the moment of the crash. The impact was so severe that the Su-30SM buried itself 6m into the ground. The black box has been recovered, but most of the aircraft has been completely pulverised.
10/ The investigators are focusing on maintainance procedures at the Irkutsk aircraft plant, which is operated by Irkut Corporation PJSC, which employed the two airmen as test pilots.
11/ The investigative committee seized items including a UGZS-M-131 unified gas charging station, a mobile system based on the ZIL-131 truck with cylinders in the back. It's used at airfields for refueling aircraft oxygen systems.
12/ It's likely they are looking at whether the equipment was faulty, or whether a failure by the ground crew to follow safety procedures led to the aircraft's oxygen supply malfunctioning. It's an expensive loss; each Su-30SM costs nearly 1.2 billion rubles ($16.3m). /end
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