？
What's the airplane's estimated time of arrival?
Literal
Airplane [possessive-の] arrival-scheduled-time [topic-は]?
到着予定時刻 is a dense four-morpheme Sino-Japanese compound: 到着 (arrival) + 予定 (scheduled) + 時刻 (time) — essentially 'ETA.' The sentence ends with は? — a bare topic marker with rising intonation, leaving the predicate implied. This elliptical style is perfectly natural in spoken Japanese.