BBC news 2010-04-16 加文本

....but also significantly, the ash can get inside the aircraft's instrument systems and under conditions where the pilots are using their instruments to fly the aircraft, they will find themselves in the very dangerous situation,  not being able to have reliable instruments.

where the pilots are using their instruments to fly the aircraft是定语从句，修饰的是conditions。where引导定语从句一般修饰的是抽象名词。

一、where定语从句修饰抽象名词point

You reach a point where medicine can’t help. 你已到了药物无法治疗的地步。

The crisis has reached a point where the receiver will have to be called in. 危机已达到非把破产管理人叫来不可的地步。

We have reached a point where a change is needed. 我们到了必须改一改的地步。

注：有时point也可以是具体的地点：

Let the point where AB cuts CD be called E. 设AB线与CD线的相交点为E。

The accident happened at the point where the A15 joins the M1. 事故发生在A15与M1交叉的十字路口。

二、where定语从句修饰抽象名词case

There are cases where the word “mighty” is used as an adverb. 在一些情况下，mighty一词可用作副词。

Today, we’ll discuss a number of cases where beginners of English fail to use the language properly. 今天，我们将讨论一些英语初学者对英语使用不当的问题。

三、where定语从句修饰抽象名词activity

Those successful deaf dancers think that dancing is an activity where sight matters more than hearing. 那些失聪的成功舞蹈演员们认为，舞蹈是一种让人看胜过让人听的活动。

四、where定语从句修饰抽象名词situation

He got into a situation where it is hard to decide what is right and wrong. 他陷入一种难以分辨是非的局面。

If you risk something important, you cause it to be in a dangerous situation where you might lose it. 你如果拿重要的东西去冒险，那你就是将它置于一种可能会失去它的危险境地。

五、where定语从句修饰抽象名词position

It’s put me in a position where I can’t afford to take the job. 这使我陷入一种不能接受此工作的境地。

六、where定语从句修饰抽象名词job

She wants a job where her management skills can be put to good use. 她想找一份能将她的管理技能派上用场的工作。

I don’t want a job where I’m chained to a desk all day. 我不想找一份整天坐在办公桌前的工作。