Based on previous monthly reports, Qantas usually release this...

Based on previous monthly reports, Qantas usually release this report on the last day of the month for the previous month's activity. The March's report was released on 18 April as Qantas wanted to advise the market early that Qantas expected the last quarter for 2016 financial year to be negative compared to the same period last year. The negative outlook was due to a federal election and depressed consumer confidence!!
Using this logic, if April's traffic numbers are worst then what Qantas signalled to the market, Qantas would have advised the market early as well.
I assume that Qantas has not advised ASX of any profit downgrades themselves is because Qantas has not given the market any profit guidelines for 2016 and as such doesn't need to advise the ASX!