Definition
The fuel tanks designated by the airplane manufacturer as the primary tanks from which fuel must be drawn during takeoff and landing. On many multi-engine airplanes, these are typically the inboard tanks, and the Airplane Flight Manual or Pilot's Operating Handbook specifies that the fuel selectors be positioned to these tanks for takeoff, landing, and certain other critical phases of flight.
Plain English
These are the specific fuel tanks the manufacturer says you must be using when taking off and landing. They are not necessarily the biggest tanks or the only tanks, just the ones required to be feeding the engines during those critical moments.
Context Anchor
Seen in fuel system descriptions, before-takeoff checklists, and fuel crossfeed procedures, especially on airplanes with more than one fuel tank or more than one engine.
Derivation
Main means principal or most important. Takeoff means the part of flight when the airplane leaves the ground. Together, the phrase points to the principal fuel tanks used for that critical part of flight.
Why Pilots Care
Correct selection prevents fuel starvation or imbalance that could affect takeoff performance or controllability.
Intuition Check
Do not read “main” as meaning “the only tanks on the airplane.” It means the primary tanks for the required procedure. Do not read “takeoff fuel tanks” as special temporary tanks; it means the tanks selected and used for takeoff.
Example Sentence 1
Before takeoff, she confirmed both fuel selectors were set to the main (takeoff) fuel tanks as required by the checklist.
Example Sentence 2
After completing crossfeed training, the pilot returns the selectors to the main takeoff fuel tanks for departure.