Complex sentence: The aircraft was cleared to land by controllers at Tashkent at around 1900 hours local time and in full darkness, by which time the weather had deteriorated significantly and the region was shrouded in fog, limiting visibility on the ground to 1300 meters.
Split into simpler sentences: The aircraft was cleared to land by controllers at Tashkent at around 1900 hours local time. The area was in full darkness and the weather had deteriorated significantly, with the airport being shrouded in fog that limited visibility on the ground to 1300 meters.