After a number of engine accidents, Russia's S7 Airlines has recently been forced to change the anti-icing procedures of its Boeing 737-800 aircraft. This change was made after communication with the Federal Air Transport Agency (FATA) of Russia.
The airline said the decision came after several accidents on its 737-800 aircraft in the days leading up to the decision. S7 Airlines said crew members reported a change in the operating characteristics of the CFM56 engines that power its 737-800 aircraft and a reduction in performance when it de-iced its 737-800 aircraft. In order to comply with safety requirements, the pilot returns the aircraft to the parking area and waits for the technician to perform additional checks on the aircraft.
Upon inspection, it was found that the cause of the deterioration in engine performance was contamination of the compressor blades due to de-icing fluid. However, S7 said the engine was fully operational in each operation and that the issue did not affect the aircraft's flights.
Subsequently, S7 Airlines decided to change its de-icing procedures when operating the 737-800 aircraft in such a way that ground crews would de-ice the aircraft only when the aircraft's engines were turned off. It is generally accepted internationally that aircraft are de-iced before take-off, including while the engines are running. In this case, anti-icing fluid can be sucked into the engine from the surface of the aircraft. This is especially common on aircraft such as the 737, which has a slightly lower engine position than other types of aircraft.
After communicating with the Russian aviation regulator FATA, the agency made three recommendations to S7 Airlines, including shutting down the engines during the de-icing process, cleaning the engines more frequently, and analyzing the situation related to other aircraft types to mitigate the risks associated with flight safety.
On December 8, 2023, an S7 Airlines Bo737-800 aircraft encountered a double-engine stall while climbing shortly after taking off from Novosibirsk International Airport. The 737-800 aircraft, registered RA-73665 and previously registered VQ-BKV, was operating flight S72502 to Moscow's Domodedovo International Airport.
It is unclear whether S7 Airlines procures spare engines or imported parts through third-party intermediaries and whether it is involved.