Definition
In a multi-tank aircraft fuel system, the master tank is the central tank from which the engine draws fuel directly, and into which fuel from other tanks is transferred before being used. Other tanks feed the master tank either by gravity, by transfer pumps, or by a fuel-balancing system, so that the engine itself is supplied from a single, consistent source.
Plain English
The main fuel tank that feeds the engine. Other tanks pass their fuel into this one first, rather than feeding the engine directly.
Context Anchor
Seen in aircraft fuel-system descriptions, especially on aircraft with more than one fuel tank.
Derivation
‘Master’ here carries its older sense of ‘the controlling or principal one,’ from Latin magister, meaning chief or head. The master tank is the principal tank in the system — the one the engine actually draws from — with the other tanks subordinate to it.
Why Pilots Care
Knowing which tank is the master tank tells the pilot how fuel actually reaches the engine. Fuel management — transferring fuel between tanks, monitoring quantities, and avoiding imbalance — is built around keeping the master tank supplied. Misreading the system can lead to fuel starvation even when the aircraft still has fuel on board.
Intuition Check
Master does not mean a separate control switch or command device here. It means the main fuel tank that directly feeds the engine fuel system.
Example Sentence 1
The auxiliary tanks transfer fuel into the master tank, which feeds the engine.
Example Sentence 2
During the flight, fuel was transferred from the wing tanks back into the master tank to maintain balance.