A flight crew is being lauded as heroes after safely landing a plane that at times was reportedly uncontrollable due to icing. An investigation is underway and preliminary findings show that the aircraft may not have been properly de-iced before departure.

On December 2, S7 Airlines Flight 5220 departed runway 10 from Magadan Airport, Russia. Onboard were 202 passengers and seven crew, bound for Novosibirsk, Russia. Shortly after departure and during climb the Airbus A321-200N’s autopilot disengaged, reports the Mongolia Air Accident Investigations Bureau. The flight crew called in a mayday as the aircraft’s instruments had discrepancies in airspeed indication. The aircraft also experienced some wide pitch oscillation swings and rolls:

The pitch attitude oscillated with -23.9° and +43.6 being the most extreme values reached. In that period the aircraft rolled left and right with the extreme values being +49.8° and -91.1°.

The aircraft rapidly climbed from 4699 feet to 14351 feet and then descended rapidly to 5084 feet. From then on altitude remained difficult to control with the aircraft reaching 13748 feet at 00:57 and down to 4556 feet at 01:06 hours.

The crew attempted to return to Magadan twice, but both landings had to be aborted. The AAIB says that the first approach was aborted at 5,000 feet while the second was aborted due to icing. A preliminary report from Russia’s Federal Air Transport Agency (Rosaviatsiya) reported by FlightGlobal says that the aircraft stalled on approach during one of the attempted landings.

Ultimately, the flight crew was able to regain control of the aircraft and diverted to Irkutsk, Russia. There, they made a safe landing 4.5 hours after departure and there were no injuries.

What caused all of this to happen?

Initial reports suggested that the aircraft was de-iced using counterfeit de-icing fluid.

The preliminary Rosaviatsiya report has come out, notes Flight Global, and what happened is a bit different. The Airbus sat for two and a half hours before departure in heavy snowfall. This led to a “large amount” of snow accumulating all over the aircraft. Airport ground crews used Type I and Type IV de-icing fluids, however they cleared only the wings and tail.

Rosaviatsiya says that the crew switched on the Airbus’ windshield heating system, which melted snow off of the windshield. That melted snow ran down the fuselage and froze into ice ridges just forward of the plane’s pitot probes.

The aircraft then departed Magadan with a thick layer of snow on the upper fuselage and engine cowlings and into a zone of turbulence and icing. “Rough ice” was also found on the leading edges of the wings after the plane made its landing.

Ice buildup can do more than just mess with systems. Too much of it can impact the wings’ lift or even get ingested into an engine. Regulations generally prevent aircraft from taking off covering critical components in snow and ice.

Both Airbus and Boeing also recommend treating the fuselage as part of de-icing and anti-icing procedures.

This isn’t the first time that an Airbus aircraft has malfunctioned due to ice buildup in front of pitot probes and the manufacturer has published an explainer on what ice buildup can do.

Airbus explains that ice ridges may form in front of pitot probes if the lower nose fuselage is not de-iced or is not completely de-iced.

A320/A330/A340 aircraft families:

- If one probe is affected, there is no associated system loss
- If two or three Pitot probes are affected, the Auto Flight System and Electrical Flight Control System may reject the 3 ADRs. This can result in the following:
- Loss of Autopilot
- Loss of Flight Directors
- Loss of Auto-thrust
- Loss of computation of the Characteristic Speeds
- Loss of the rudder travel limiter function
- Reversion to manual Alternate Law.

At this time it’s not known exactly why the plane flew so erratically early on, but the discrepancies in instrument readings were likely caused by the ice ridges. Rosaviatsiya is recommending that ground crews do not release planes until snow has been removed.