Read the fragment: 'O aeroporto amanheceu vazio; os voos haviam sido cancelados durante a madrugada.' The form 'haviam sido cancelados' (pluperfect compound) situates the cancellation:

1. At a moment prior to another past reference point — before the morning the airport was found empty
2. At exactly the same time as the discovery of the empty airport
3. After the airport was found empty, as its consequence
4. In a future moment relative to the narration