Definition
A federal labor regulation that limits how long an airline flight crewmember may be kept on duty away from their home base. Once a crewmember has been on duty long enough that further assignments would exceed allowable duty or flight-time limits, they are 'hooked' and must be returned to base or given required rest before flying again.
Plain English
A rule that says an airline crew can only work so many hours away from home before the airline has to stop assigning them flights and send them back or let them rest.
Context Anchor
Used in aircraft maintenance, especially when laying out, checking, or fabricating parts where measurements must start from the edge of the material.
Derivation
The term comes from the idea of being 'on the hook' — caught by a limit you cannot work past. Once the crewmember hits the regulatory ceiling, they are hooked and the airline's options are constrained.
Why Pilots Care
A blade that violates the hook rule can produce severe vibration and may fail in flight.
Analogy
It works like the hooked end of a tape measure: the hook gives you a firm starting point so the measurement begins exactly at the edge.
Intuition Check
Do not read “rule” here as a regulation or procedure. In this term, “rule” means a measuring ruler, and the hook is a physical part of the tool.
Example Sentence 1
The first officer was hooked under the Hook Rule after the long weather delay, so dispatch had to assign a fresh crew for the return leg.
Example Sentence 2
The hook rule told the pilot the propeller had to come off before the next flight.