We waited until the plane _____.

Until এর পূর্বে past form থাকলে এর পরে past perfect tense হয়।

যেমন:
- I waited until the train had left the station.
- He waited until she had finished speaking.
- She waited until her coffee had cooled down before taking a sip.

সুতরাং, প্রশ্নোক্ত বাক্যের শূন্যস্থানে হবে - had taken off

Source: Longman Dictionary of Contemporary English