飛行機

How it works

が (subject) marks 飛行機(ひこうき) (airplane) as the thing being noticed. The verb 見える(みえる) (be visible) already means “can be seen / comes into view” on its own, and here it shifts to plain past 見えた(みえた) (came into view) — so this is a casual “an airplane came into view,” not “I looked at it on purpose.”