Six people fell from the top of boarding stairs at Barnaul (BAX) airport in Russia, as Ural Airlines passengers were boarding for a flight to Moscow. Local authorities have opened a criminal investigation into the cause of the incident.

Passengers of Flight U6652 were about to enter the Ural Airlines’ Airbus A320 (VQ-BFV) in the early morning (7.20 am) on February 12, 2019, when the boarding stairs basket collapsed. Six people fell from approximately 11 feet 42 inches (3.48 meters) height to the tarmac.

Investigating authorities claim four of the unlucky passengers sustained injuries “of varying severity” and were hospitalized. The airline representative, quoted in several local media, claims that only three passengers required hospitalization and that the rest were  “not injured” during the incident.

“According to preliminary data, the reason for the fall is the broken construction of the self-propelled passenger stairs, which is owned and serviced by the airport,” an airline spokesperson is quoted as saying by state news media.

On February 12, 2019, the West Siberian Investigation Department for Transport confirmed opening a criminal case. Now, the investigating authorities are looking into the circumstances of the incident, in particular, performing a “provision of services that do not meet safety requirements [of consumes’ life and heath], resulting in injury to passengers of the flight”.

The incident comes almost exactly a year since another Russian aviation tragedy. On February 11, 2018, an Antonov An-148, belonging to Saratov Airlines, crashed minutes after take off at Moscow’s Domodedovo airport (DME), killing all 71 persons on board.

It is not the first such striking incident for Ural Airlines. In September 2017, passengers were disembarking the airline’s  A321 aircraft at St. Petersburg airport (LED) when a boarding stairs platform collapsed. Two passengers – a mother with a one year old child – fell down, sustaining serious injuries. The child later died in  the hospital.