A preliminary investigation into the serious in-flight disruption of an S7 Airlines Airbus A321neo revealed that the aircraft suffered a disruption of three air data systems shortly after takeoff from Magadan, resulting in discrepancies in speed information and consequent control problems.
The plane – bound for Novosibirsk on December 2 – was carrying 202 passengers and seven crew members.
Freezing conditions, including heavy snowfall and a temperature of minus 9 Â° C, were present in Magadan on departure, and the Federal Air Transport Authority Rosaviatsia states that de-icing treatment was carried out on the jet. before take off.
Although the crew initially chose to return to the airport, the A321neo stalled during its descent and approach to landing, and the crew instead opted to divert to Irkutsk – a 4 hour flight away – where he landed safely.
Inspection of the aircraft revealed rough ice on the leading edges of the wing and ice ridges were also present on the forward fuselage, in front of the pitot-static ports, as well as the radome.
The formation of ice ridges on the fuselage “distorts” the airflow to the pitot-static system and its pressure sensors, resulting in unreliable airspeed readings, Rosaviatsia explains.
The authority has yet to detail the circumstances of the incident involving the aircraft (VQ-BGU), but a flight data recording document appeared online shortly after the event, which appears to show that the aircraft experienced excessive pitch and roll shortly after departure.
Although its authenticity has not been officially verified, the basic data is consistent with the trajectory of the aircraft after take-off from Magadan.
This suggests that the aircraft initially climbed to about 8,700 feet but suffered a degradation in its flight control laws. The flight data recording appears to show rapid fluctuations in altitude, from about 5,000 feet to 14,000 feet, bank angles ranging from about 40-50 Â° to 91 Â°, and pitch variations of 24 Â° to dive at 43 Â° with your nose in the air.
Rosaviatsia points out, in a safety bulletin, the need to monitor compliance with de-icing processes to ensure planes are clean, listing a number of incidents and past accidents attributed to ice build-up.
Although it does not have detailed conclusions on the cause of the incident, the bulletin stresses that ground handling personnel should pay attention to the periods of validity of the de-icing fluid protection, ensure that the Fluid application is carried out in strict accordance with manufacturers’ flow data, that different fluids are not mixed unless approved, and de-icing vehicles are properly maintained.
Rosaviatsia also recommends that crews and ground support agents of A320 Family aircraft familiarize themselves with the manufacturer’s information on preventing the formation of frost on the front fuselage.
Airbus previously said ice ridges can form in front of the pitot-static system if the aircraft has been parked for a long stay in cold conditions – most accretions occur before the first flight of the day – or can appear as slush from the heated windshields. freezes again when moving down the fuselage.
Ice ridges in front of the Pitot probes can disrupt airflow, he adds, and cause the air data system to indicate speeds below the actual speed.