Bonjour Daba, This is a very good question. I see no reason that the verb aller cannot be used in the same phrase. The fact that partir is used leads me to believe that it has more to do with agreeing of the past participle in phrases that use «on» as the subject. However, I am uncertain what difference it would make with whichever verb was used. Perhaps someone from the Kwiziq team will be able to provide a more informed answer. Bonne chance.