A little known feature called ‘flights data detector’ (not highlighted on stage during Apple’s WWDC keynote) is included in both iOS 9 and OS X El Capitan. The feature currently works with Mail, Messages, and Notes, and it only works with the most recent/current flight. This feature lets iOS automatically detect when text is referencing a flight and allows users to actually check on the flight’s status and progress with an attractive interface.
This is how the feature works:
Step 1: Open Notes App and tap to create a new note.
Step 2: Start typing both the airline and flight number including the number sign into a text field (example: Virgin Atlantic #75) Hit a space or Return. After typing each airline and flight number, iOS 9 automatically recognized the data format as an existing flight and created an actionable link out of the text.
 

via: Reddit
The same functionality should also be available from emails containing itineraries from airlines. Some users reported that El Capitan and iOS 9 also does the same with package tracking. Most (if not all) shipment tracking numbers will have the popup.
But asking Siri “What is the status of Virgin Atlantic  flight no 75” returning a normal web search via Bing, which may be the case that this this is not yet implemented for voice?
While this won’t replace a dedicated travel app, it’ll be handy if you want to check for flight delays or satisfy your curiosity about an airplane’s location.