Russia's federal aviation regulator has disclosed that it was forced to ground Saratov Airlines because it failed to meet the necessary standards of air transport safety.
Rosaviatsia says it provided the carrier with the maximum 90 days permissible under Russian aviation law to implement in full recommendations aimed at addressing shortcomings discovered during inspection of the airline's operations.
"During this time the management of Saratov Airlines was not able to eliminate the violations," says the regulator.
Inspection of Saratov Airlines, following a fatal accident involving one of its Antonov An-148s in February, turned up "significant" violations in its flight operations activities, states Rosaviatsia.
Saratov had been granted temporary validity of its air operator's certificate but this expired on 30 May.
Rosaviatsia says the certificate has been "cancelled" as of 31 May. Checks on flight activities and documentation of crew members for March-April this year, conducted on 26-27 May, showed that the weaknesses persisted and were systemic.
Crew scheduling and rostering did not take into account duty-time requirements. Insufficient checks are conducted on pilots and fatigue-management measures are inadequate, the regulator found.
"The airline does not meet safety requirements and is not able to carry out transportation without risks to its passengers," it adds. "The priority of [the regulator] was to keep the airline in unconditional compliance with all safety requirements."
Fatigue reduces crew alertness, it says, and causes loss of spatial orientation, situational awareness, and comprehension of control systems.
Investigators are still probing the An-148 accident but have determined that the crew failed to activate the pitot-static heating system before the aircraft departed Moscow Domodedovo. The crew received unreliable airspeed indications and subsequently lost control of the jet.
Saratov Airlines' An-148 fleet had already been suspended from service in the wake of the crash. The airline had been bringing in Embraer E-Jets to reinforce capacity.