The plane stalled, flipped over onto its back and crashed near the perimeter.
飞机失速了，翻了一个跟头，坠毁在机场环形围栏附近。
Guards had been posted at several points around the perimeter.
在环形防线上已布置了几处岗哨.
The barbed wire fence round the perimeter discouraged intruders.
周围有铁丝网阻止了外人闯入.
