Definition
A condition in which a pilot or crewmember is mentally and physically able to perform assigned flight duties safely, free from the effects of fatigue, illness, alcohol, drugs, emotional stress, or any other factor that could impair judgment, coordination, or reaction time.
Plain English
You are in good enough shape -- physically and mentally -- to fly safely right now. Nothing is going on with your body, your mind, or your recent choices that would put you, your passengers, or anyone else at risk.
Context Anchor
Used in pilot self-assessment, crew scheduling, maintenance work, and any situation where a person must decide whether they should perform an aviation duty.
Derivation
Fit comes from an older English sense meaning suitable or proper for a purpose. That helps here because Fit For Duty is not about general athletic fitness; it is about being suitable and safe for the specific duty at hand.
Why Pilots Care
Ensures legal operation of the aircraft and reduces risk of fatigue or impairment causing accidents.
Intuition Check
Fit For Duty does not mean merely being physically strong or showing up for work. In aviation, it means being safe and able to perform the required duty right now.
Example Sentence 1
After being up most of the night with a sick child, the captain determined he was not fit for duty and called in a replacement.
Example Sentence 2
After exceeding the maximum duty time, the pilot was no longer considered fit for duty and had to rest.