Following an accident, we always look at a number of factors to see whether fatigue could have played a role in the incident. For example, we look at the time of day when the incident occurred. During some parts of the day, such as the late afternoon or middle of the night, there's a normal decline in physiological performance caused by fatigue. We look at how many hours the crew or pilot were up, how many hours they worked, when they went to sleep and how long they slept. We look back up to 72 hours to see whether fatigue was present. Even if fatigue was present, that doesn't necessarily mean it contributed to the accident. We look at the two factors, but we do so in a very scientific way.
On April 4th, 2017. See this statement in context.