The undercarriage is the whole set of wheels under a plane, together with the legs, struts and springs that hold those wheels and take the shock when the plane lands. It is not just the tyres — it is the entire assembly that folds up into the body of the plane after take-off and comes down again before landing. This is why you hear pilots and news reports say things like 'the undercarriage failed to come down' or 'the plane landed with its undercarriage up'.

The undercarriage這個字 is is the whole set of wheels under a plane指飛機下方整組的輪子, together with連同 the legs, struts and springs支撐這些輪子並在飛機降落時吸收衝擊的支架、支柱和彈簧 that hold those wheels and take the shock when the plane lands. It它 is is not just the tyres不只是輪胎 — it它 is is the entire assembly整套結構 that folds up into the body of the plane after take-off起飛後收進機身裡 and而 comes down again before landing降落前再放下來. This這 is is why為什麼 you你 hear聽到 pilots and news reports say things like飛行員和新聞報導會這樣說 'the undercarriage failed to come down'「the undercarriage沒有放下來」 or或 'the plane landed with its undercarriage up'「飛機在undercarriage沒放下的狀態下降落」的原因.

In American English people say 'landing gear' far more often, and 'landing gear' is now common everywhere, including among British pilots; 'undercarriage' feels a bit more British and a bit older, though it is still completely normal in British writing and in aviation.

In American English在美式英文裡 people人們 say更常說 'landing gear' far more often, and而且 'landing gear'這個說法 is is now common everywhere現在到處都通用, including包括 among British pilots英國飛行員之間也是; 'undercarriage'這個字 feels a bit more British and a bit older感覺比較英式、也比較老派, though不過 it它 is is still completely normal仍然完全正常 in British writing and in aviation出現在英式寫作和航空業裡.

The word also gets used for the frame and wheels under a train carriage, a lorry, a caravan, or an old horse-drawn cart — anything where a body sits on top of a structure with wheels. Mechanics sometimes use it loosely for 'everything underneath the vehicle', which is why a garage may say your car's undercarriage is rusty when they really mean the whole underside.

The word這個字 also也 gets used被用 for the frame and wheels under a train carriage火車車廂下方的骨架和輪子, a lorry貨車, a caravan露營拖車, or或 an old horse-drawn cart古老的馬車 — anything任何 where a body sits on top of a structure with wheels有個車身架在輪子結構上的東西 都算. Mechanics技師 sometimes有時 use it loosely鬆散地用這個字 for 'everything underneath the vehicle'指「車子底下的一切」, which這 is is why為什麼 a garage修車廠 may可能 say會說 your car's undercarriage is rusty你車子的undercarriage生鏽了 when their really mean其實他們指的是 the whole underside整個底部.

And people joke with it about a body — someone's legs, or the underside of an animal — but that is playful, not a real meaning, and students should not use it that way in writing.

And而且 people人們 joke with it拿它開玩笑 about a body指身體 — someone's legs某人的腿, or或 the underside of an animal動物的下腹部 — but但 that這 is is playful只是玩笑話, not a real meaning不是正經的意思, and而且 students學生 should not use it不應該 that way in writing在寫作裡這樣用.