N4161 - Incident: Nordwind A321 and S7 B738 near Rostov on May 29th 2021

A Nordwind Airbus A321-200, registration VQ-BRL performing flight N4-161 from Moscow Sheremetyevo to Krasnodar (Russia), was enroute at FL330 about 60nm north of Rostov (Russia) when ATC queried the crew whether everything was normal on their flight deck.

At the same time a S7 Siberian Airlines Boeing 737-800, registration VP-BLD performing flight S7-2043 from Moscow Domodedovo to Sochi (Russia), was enroute at FL350 about 60nm north of Rostov (Russia), when ATC also queried that flight about whether everything was normal on their flight deck.

Both flight crews reported operations were normal, nothing unusual on their flight decks, both flights continued to their destinations without further incident.

On May 30th 2021 Rosaviatsia reported the radar controller received indications both flights had transmitted the code for unlawful interference via their transponders. This however was identified as a malfunction of one of the radar heads used by the enroute traffic center.

Mode-S data received do not show any such transponder code for unlawful interference from any aircraft, both aircraft show the same transponder code throughout their flights.