Complex sentence: It has been slow to start services and its Boeing 727 was parked at Belgrade since October 2004 until recently, but for some time was used by Aviogenex under Serbian registration of YU-AKD.
Split into simpler sentences: It has been slow to start services and its Boeing 727 was parked at Belgrade since October 2004 until recently. Their Boeing 727 was used by Aviogenex under Serbian registration of YU-AKD.