When will air transport industry take off in full swing again?

As soon as the restrictions lift. Realize there is tremendous pent-up demand from people who need to travel but who have not been able to. 

Two years from now.  Airlines will not be allowed to run at full capacity until 80% of us have been given a vaccine.  Same with international travel.  Mandatory 14 day quarantine for international travellers until a vaccine.   It's the reason why Warren Buffet dumped all his airline stocks.  There will be at least one major airline going bankrupt.