Learn Italian: È un peccato che il tuo volo non parta oggi. - It is a pity that your flight is not departing today.

The phrase È un peccato che (It is a pity that) expresses an emotion or subjective attitude. In Italian, when you introduce a clause with an expression of emotion followed by che (that), it triggers the subjunctive mood for the next verb.

Parta looks like an -are verb. Why does an -ire verb like partire end in -a here?

In the present subjunctive, the vowel endings swap compared to the normal present tense. For -ire and -ere verbs, all the singular forms (I, you, he/she/it) end in -a. Since the flight (il volo) is a third-person subject (it), the correct subjunctive form is parta.

Why do we need the article il in il tuo volo?

Unlike English, Italian requires a definite article before possessives in almost all cases. The main exception is with singular close family members (like mio fratello). Since a flight is not a family member, you must always use the article, making it il tuo volo.

Can È un peccato che be used with the normal indicative tense if the flight delay is a definite fact?

No, the expression of emotion itself is what triggers the subjunctive, regardless of whether the event is a hard fact. Even though it is a proven fact that the flight isn't leaving today, your emotional reaction to it (È un peccato che) forces the verb into the subjunctive.