Steel does ×1 to Flying

Generations VI to IX, single types. The other way round, Flying against Steel, is ×½.

65 Steel and 109 Flying species among the 1025 this site covers.

Attacker, Grass and Steel Kartana sprite

Kartana #0798

damage×1Generations VI to IX

Defender, Psychic and Flying Lugia sprite

Lugia #0249

Steel did not exist in Generation I, so Steel against Flying has no value there.

Strongest Steel attackers

Kartana leads Steel at Atk 181

Sturdiest Flying defenders

Dual types that change the answer