Definition
A takeoff conducted when both the reported ceiling and visibility are effectively zero — no cloud base above the runway and no forward visibility along it. Such departures are not authorized for Part 121 or Part 135 operations and are generally prohibited or strongly discouraged for Part 91 operators because of the inability to see and avoid obstacles, maintain runway alignment, or return to land in the event of an emergency shortly after takeoff.
Plain English
Taking off when you cannot see the cloud base or down the runway — essentially launching into solid fog or cloud right from the ground.
Context Anchor
Seen in instrument departure planning and takeoff minimums discussions, especially when considering whether the weather is safe and legal enough for departure.
Derivation
The expression 'zero/zero' comes from reporting weather as two numbers — ceiling and visibility. When both read zero, pilots simply call it 'zero/zero.' The phrasing stuck because it captures the worst-case visual condition in two short words.
Why Pilots Care
Such conditions are normally prohibited or require special authorization because they eliminate all visual references at the moment of liftoff.
Grounding Statement
Picture starting the takeoff roll into dense fog so thick that the runway lights disappear almost as soon as the aircraft begins moving.
Intuition Check
Zero/zero does not mean a precise mathematical condition that must be exactly zero in every report. In this context, it means conditions are so low that the pilot has essentially no outside visual reference for takeoff.
Example Sentence 1
The captain elected to delay departure rather than attempt a zero/zero takeoff in dense fog.
Example Sentence 2
Standard takeoff minimums do not permit a zero/zero departure without an approved waiver.