Originally Posted by Often1

On early AM flights, often means that the crew hasn't had its FAA-mandated rest (sleep) period. Last night's flight got in late and the AM flight is too early.

Nobody doubts that UA told you that the delay was for "crew missing." But unless you know why the crew isn't at the aircraft, you have no way of saying whether the delay was or was not avoidable.

Crew on legally required rest due to late arrival is a lot different than crew is too drunk to fly.