First of all, you can only have passive sentences with transitive verbs. (i.e., verbs that need an object) And the confusion about whether a past participle is an adjective or not mainly happens when the pp follows the verb be (or a form of be). Unfortunately, this is also the form of the passive.
You could easily turn your sentence into an active sentence: “Bad weather delayed the flight.” / “The air traffic controllers delayed the flight due to bad weather.” So there is a good argument that your sentence is passive.
A common place to see a past participle used as an adjective is before the noun:
- a delayed flight
- a well-known song
- a fried egg
- a bored student 8)
If the only verbs in the sentence are be (or a form of be) and a past participle, then you have to do a little thinking to decide whether it’s a passive sentence or not. Sometimes you can look at it both ways. BUT…
If you can easily add “by whom” to the sentence, then it’s probably passive. And if the past participle can’t be used as an adjective in front of the noun, then it’s doubly clear that it’s a passive sentence.
For example, the sentence “America was discovered in 1492” can only be seen as a passive sentence. ("…discovered by Columbus", even though Columbus is not mentioned in the sentence.)
Does that help? Do you have more “past participle” sentences that you find confusing?
Present participles are also used as adjectives. :lol: