定语从句，关系代词什么时候需要紧跟先行词？

先行词与定语从句隔离

定语从句一般紧跟在先行词之后，但定语从句与先行词之间有时也会插入别的成分，构成先行词与定语从句的隔离。例如：

1) This is the article written by him that is poke to you about..

2) He was the only person in this country who was invited
3)A new master will come tomorrow who will teach you German. 明天要来一位新教师教你们德语了。（关系代词who引导的定语从句与其先行词master分离）

其实就是句子顺序倒了一下, 你那句子不也可以写作:
Airplane,which usually employed in transporting people,is the most effective means of transportation吗?那就挨着先行词了

只是两种不同的表达方法..不用那么仔细去区分的..

就像这种，which引导的非限定性定语从句

which引导的