Russian inspectors have determined that Russian carrier Red Wings has been exceeding maintenance interval limits on its Tupolev Tu-204 fleet.
Federal air transport authority Rosaviatsia states that an inspection of the carrier found "violations" of flight operation regulations, including breaches of duty-time and rest periods for pilots.
Crews on long-haul services were wrongly reinforced with trainee co-pilots, it adds: "Under current law a trainee co-pilot cannot be seen as augmentation of the crew."
But Rosaviatsia says it also discovered irregularities in maintenance on four Tu-204s, half the Moscow-based airline's fleet.
It turned up a "considerable exceeding" of periodic maintenance intervals on the type. The airline had allowed 773h to pass between maintenance checks, compared with the standard interval of 600h, plus or minus 60h.
"In other words, flights were carried out on the defective aircraft," the regulator claims, following the inspections undertaken between 13 and 26 March.
Rosaviatsia says it has yet to reach any decision on the company's future operations, given the findings. Red Wings has yet to comment on the matter, but the authority says it should immediately turn its attention to eradicating the deficiencies.
Red Wings is the launch customer for the Tu-204SM programme, a modernised version of the baseline twinjet.