Annoyingly, this also happened the last time I flew with a bike – although that time the damage was limited to two chainrings and a set of handlebars.

懊恼的是，上次我携自行车飞行时，也遭遇同样情况，只不过，那次的损失仅限于车链轮及车把手。

youdao

Derailleur gears have a front mech (short for front gear mechanism) to shift the chain between two or three chainrings and a rear mech (short for rear gear mechanism) with up to 10 sprockets.

BBC: Sport