(~s)
If something is at a particular ~, it is at that height above sea level.
The aircraft had reached its cruising ~ of about 39,000 feet...
N-VAR: oft N of n
(~s)
If something is at a particular ~, it is at that height above sea level.
The aircraft had reached its cruising ~ of about 39,000 feet...
N-VAR: oft N of n
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012