When searching on Orbitz for round-trip flights, I see a number of results with this note highlighted in yellow when expanding Flight Details:
"This flight is pending government approval."
What does that mean? How does the likelihood that such flight will occur compared to other flights along the same route? What should I expect if it does not occur, compared to the cancellation of a flight without that note?
If an airline is planning to open a new route, especially international routes, they will need a long list of approvals before they can operate that route. Usually this process is a bureaucratic process since it involves many organizations (civil aviation authorities, airport authorities, etc.).
Anyway, airlines usually have a green light to open the route before the paper work is done, hence they start advertising that route before they get the final approvals on paper. So generally speaking it is safe to book these flights, but just in case something goes wrong, the airline is notifying you in advance about that. Also, you will get a full refund in case things go wrong.
It quite literally means that the airline is planning on launching an international route, but can't legally operate the flight until various government approvals are received. In international flights, the originating and destination countries must agree to grant an airline the right to operate a route (often including the departure and arrival time slots as well).
You also ask:
How does the likelihood that such flight will occur compared to other flights along the same route?
That's for you to decide; for me, if the airline is a major one (e.g., BA, AA, CX, JL), I'd figure the likelihood is quite high and would and have booked tickets before final approval.
What should I expect if it does not occur, compared to the cancellation of a flight without that note?
You should be treated the same, meaning that if you have a paid ticket, the airline will offer you a full refund or reaccommodation on another flight.
