The OP is making a classic error in assuming that suppliers of goods should use a "cost plus" methodology in determining the price at which they would sell a product. That simply is not how companies who are "good" at pricing do things. The price gets established by the marketplace - simple supply and demand.

AC and other airlines know that there will be high demand at the end of June to HKG due to returning students, so they raise the price. That does two things:
It allows them to earn more money on the route at that time, which will make up for the losses they incur with emptier planes with lower average revenue per seat flown at times of low demand and given that there is likely more demand than supply at that time.
The more price sensitive travellers will leave early or late to avoid the higher fare, freeing up seats for those people who value their travel dates more highly - spreading out demand.

Note: the same thing happens for travel anywhere at Christmas and in North america during the summer.

I don't cconsider this type of behaviour to be "profiteering" or "price gouging".