that(implying emotional negativity towards an event that would happen in a possible future or that already happened in the past)
Я бою́сь, ка́к бы они́ не опозда́ли на игру́.
Ja bojúsʹ, kák by oní ne opozdáli na igrú.
I'm afraid that they will be late for the game.
Они боя́тся, ка́к бы он не заблуди́лся.
Oni bojátsja, kák by on ne zabludílsja.
They fear that he may lose his way.
Ку́рица убега́ет из стра́ха, ка́к бы волк не стара́лся пойма́ть её.
Kúrica ubegájet iz stráxa, kák by volk ne starálsja pojmátʹ jejó.
The hen is running away out of fear that a wolf is trying to catch it.
Usage notes
The main clause needs a meaning that pertains concern, fear, horror, or worrying. It is often used with the verb боя́ться(bojátʹsja) or беспоко́иться(bespokóitʹsja), but it is also used with nouns such as беспоко́йство(bespokójstvo), боя́знь(bojáznʹ), опа́сность(opásnostʹ), опасе́ние(opasénije), страх(strax), etc..
The main verb in a subordinate clause that starts with как бы не has a perfective aspect. And as with бы(by), the main verb takes the past tense form when it is finite.
If the main clause and the subordinate clause that starts with как бы не have the same subject, then the subordinate clause can have its main verb as an infinitive without a subject (as the missing subject is already implied in the subject of the main clause). For example:
Мой коллега беспокоился, как бы она не встретила своего менеджера. (My collegue was being worried that she met her manager.)
Мой коллега беспокоился, как бы не встретить своего менеджера. (My collegue was being worried that she met her manager.)
The main clause can be implied by omitting it, especially when it is used in a colloquial setting. For example:
Я боюсь, как бы не пошёл дождь. (I'm worried if it's going to rain.)
Как бы не пошёл дождь. ((I'm worried) [I]f it's going to rain.)