On 25 February 2010, an Airbus A320-200 being operated by Aeroflot on a scheduled passenger flight from Oslo to Moscow Sheremetyevo successfully took off in normal daylight visibility from an unobstructed taxiway parallel to the designated departure runway 01L. The flight was a line training sector for the First Officer and a Safety Pilot was occupying the flight deck Observer. The flight crew reported that they had not appreciated that they had taken off from the taxiway until informed of this by ATC after take-off.