The crew of the Su-30 fighter jet, which crashed into a residential building in Irkutsk in 2022, suffocated due to nitrogen entering the aircraft`s onboard oxygen system.
The official cause of the 2022 Su-30 fighter jet crash in Irkutsk, where the aircraft struck a residential building, has been confirmed as pilot asphyxiation. This was stated by Alexey Alexandrov, head of the Eastern Interregional Transport Investigation Department of the Investigative Committee, in an interview with Interfax-Siberia.
He further explained that forensic examination results indicated the Su-30 pilots lost consciousness and succumbed to asphyxiation because nitrogen was supplied to the onboard oxygen system instead of pure oxygen.
Alexandrov noted that the case is still under investigation, and six employees of the Irkutsk Aviation Plant have been charged with abuse of power and negligence. According to RIA Novosti, the presence of nitrogen in the oxygen cylinders may have been due to a ground staff error.
Air Force Major and flight instructor Andrey Krasnoperov commented on the incident:
— At the factory, the oxygen system is routinely disinfected with nitrogen. Before assembly, this system must be purged to remove the nitrogen. However, in this instance, the nitrogen was not removed. When the pilots entered the cockpit and connected their oxygen masks, they were supposed to receive pure oxygen, which is a standard safety procedure. Instead, they inhaled nitrogen, leading to loss of consciousness and death. Another pilot who approached the Su-30 observed the crew members slumped forward, indicating they had lost consciousness. The aircraft was fully functional and continued flying on autopilot, making several landing attempts until it ran out of fuel and crashed. Essentially, the cause was clear from the outset, but now it has been officially declared: pilots don`t just slump over for no reason.
— Speaking of autopilot: is there one on the Su-30, and could it have been used to return the aircraft to base?
— It can initiate the landing approach, but for it to land, the pilot needs to disengage the autopilot and manually land the aircraft. Unfortunately, it cannot land itself yet.
— Returning to the causes: how could the nitrogen have gotten in?
— The specific specialist was supposed to turn on the system, connect the mask to their face, and personally breathe what was there, understand? Most likely, they didn`t do that, thinking everything was fine, but they should have opened and purged the system to ensure pure oxygen was flowing. If they had inhaled nitrogen themselves, they might have collapsed right there in the cockpit, and this disaster wouldn`t have happened. In my memory, there were cases when the system was disinfected with alcohol, but the alcohol was supposed to evaporate. A pilot once boarded, was supposed to fly at 3,000 meters, was cleared for 4,000, and had to switch to oxygen. In that situation, it wasn`t nitrogen, but alcohol; he inhaled alcohol vapors and was “dead drunk.” He still managed to land safely, but now they disinfect with nitrogen.
The Su-30 crashed in the autumn of 2022, striking a two-story private house in Irkutsk. Both pilots perished in the incident. Fortunately, the homeowners were unharmed as they were elsewhere at the time of the crash. The crashed fighter jet was not carrying any ammunition, as it was on a test flight.
Rupert Blackwood 
Clement Ashworth