The CAA insists pilot fatigue is not a safety concern.

BBC: Plane taking off

For every job, staff must select the most appropriate pilot and ensure the pilot is working within his or her fatigue management guidelines.

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According to Agence France Presse, a New Zealand Civil Aviation Authority document said the pilot, who has not been named, had voluntarily submitted a fatigue report, blaming the incident on having a bad night's sleep in London the night before.

BBC: Air New Zealand pilot 'fell asleep' during flight