Learn French: Nous voulions atterrir à Paris, mais il y avait une tempête. - We wanted to land in Paris, but there was a storm.

In the imparfait, vouloir simply describes an ongoing state of mind or intention in the past ("we wanted to"). If you used the passé composé (nous avons voulu), it would imply a specific, completed attempt or a sudden decision, which often translates to "we tried to" or "we decided to." Here, their ongoing intention to land was thwarted by the weather.

Based on the tenses used, did the plane actually land in Paris?

Probably not. Using the imparfait voulions indicates that the desire existed, but it crucially doesn't confirm that the action was ever completed. Combined with the obstacle of the storm (mais il y avait une tempête), the strong implication is that their intention was interrupted and they had to land elsewhere.

Why is il y avait also in the imparfait? Could we say il y a eu?

il y avait sets the scene, describing an ongoing background condition (the storm was already happening while they were flying). If you used the passé composé (il y a eu une tempête), it would mean the storm suddenly struck or occurred as an isolated, completed event.

Do we never need a preposition like à or de between voulions and atterrir?