空姐 is informal and specifically refers to female flight attendants. The gender-neutral formal term is 空乘 (kōngchéng, cabin crew) or 空中乘务员 (kōngzhōng chéngwùyuán). The male equivalent is 空少 (kōngshào).
memory
空 (kōng, air/sky) + 姐 (jiě, older sister) — 'sky sister,' a casual and affectionate way to say female flight attendant.
