The plane flew just barely over the control tower.

Literal

Airplane [topic-は] control-tower [possessive-の] above [path-を] barely flew.

すれすれ is a mimetic adverb meaning 'just barely, by a hair's breadth,' used for near-misses and close calls. 管制塔 (かんせいとう, 'control tower') is an aviation compound. The を marks the path of flight rather than a direct object.