Learn Farsi: در صورت فرود روی دریا، باید جلیقه بپوشید. - In the event of landing on the sea, you must put on a vest.

The phrase dar surat-e means in case of or in the event of. It is always followed by an Ezafe to link it to the next word. Here, it connects to the abstract noun forud (landing), creating the formal condition dar surat-e forud (in the event of landing).

Why is there an Ezafe after ruy?

The word ruy (on) functions as a preposition of place. In Farsi, most prepositions of place require an Ezafe to connect to the noun that follows them. So, it becomes ruy-e darya to mean on the sea.

Why does the verb bepushid take the subjunctive mood here?

The verb is in the subjunctive mood because it follows the modal verb bayad (must). In Farsi, the action that you must do is always placed in the subjunctive, which is marked here by adding the be- prefix to the present stem of the verb.

The English translation says put on a vest, but there is no word for a in the Farsi sentence. Why?

In Farsi, an indefinite object does not strictly need an indefinite marker like -i or yek if the general category is what matters. Saying jeliqe bepushid focuses on the action of putting on vest-type clothing, which is perfectly natural for a general instruction.