Flight square

A flight square is a square to which a threatened piece can retreat without remaining in immediate danger. The term is used most often for the king, especially when it needs to escape check, a direct attack on the king that must be answered immediately.

For a square to be a legal king exit, it cannot be occupied by a friendly piece or attacked by an enemy piece. Being empty is not enough: attacks from pawns, knights, line-moving pieces such as bishops, rooks, and queens, and the enemy king must all be checked. If the king is in check, the move must also remove that check completely.

An exit may exist before any threat appears. Giving the king another route reduces a back-rank weakness and may release a rook that was tied to defense. A flight square can also be created at the critical moment by a pawn move, a capture, or moving a piece that blocked the route.

Luft is escape space often created by a pawn move, usually for a king moved to one wing through castling, the special king-and-rook move. The ideas are related but not identical: the flight square is the specific legal destination, while luft describes the air or space opened around the king.

How to verify an exit

1. Identify the candidate square.
2. Confirm that no friendly piece occupies it.
3. Check every enemy attack on that square.
4. Consider what threat will follow after the king moves.