It seems like it never happened and that does all the time now. Yesterday for a departure in a week, a flight's time changed to two hours later. At some point, a departure for six months from then moved up two hours. Why do such changes take place? Is there a reason for such madness? What motivate airlines to make a single one time change months in advance?

Moving the thread to TravelBuzz.

NewbieRunner
Co-moderator, CommunityBuzz

Are you sure it really is just a single, one-off change? Most likely the airline changed their whole weekly schedule from a certain point in time onwards. It can happen for a multitude of reasons such as for example: choosing to fly different planes on this route, adding or removing other routes flown with the same plane, changes to flight paths or availability of airport facilities.

While changes well in advance tend to correlate with broad rescheduling, I'm taking a flight tomorrow that a week in advance was rescheduled for two hours later. Not any other flight the same week and not the flight on the day a week later, just that one flight.

I have no idea why that would happen, but I'm sure lots of passengers on this trans-Atlantic flight are upset.

Yeah, that is more interesting. Was the arrival of the aircraft from previous flight also rescheduled? Was there an equipment change? Different tail number than usual? (Some of this you can only know after the flight.)

Since you say it's tomorrow, I was also about to ask if you'll be flying over the South China Sea but I see it's a trans-Atlantic flight now. Maybe you can try to ask the FAs once onboard?

The good news is, on a long-haul flight late departure doesn't necessarily mean late arrival: it might very land not much later than it was originally scheduled to.

All aircraft make many flights a day. Just moving one flight would disrupt that chain of flights, so it's extremely unlikely that "a single one time change" was made.

Airlines are always evaluating flight loads, competition, etc., and evaluating changes to number of flights, type of plane, destinations served, etc. Any time a change is made, the process that optimizes the use of aircraft, crew, etc., etc., need to be executed. An airline can't just add an extra DFW-ORD flight. It needs to have a plane to fly, that comes from somewhere, and goes somewhere after. Same with crew. Thousands of pieces of equipment/crew need to be optimized. And when one piece of the puzzle changes, it has impacts on other parts of the schedule.

So the reason for the "madness" is a company trying to run a profitable and efficient airline.

Look at the 2nd and 3rd flights which are at irregular times.

GIG-LIS Mon 7/10 5:40p-7:20a
LIS-GIG Tue 7/11 11:35a-5:35p
GIG-LIS Tue 7/11 7:50p-9:30a
LIS-GIG Wed 7/12 10:05a-4:10p

It occured to me that Portugal had to finish the UEFA soccer game against France (and won!), and after a restful night's sleep, maybe the time needed for them to pack was projected to delay the flight to the olympics in Rio two hours. Do you think this makes sense?

Added 7/12: the reason the Tue LIS-GIG was scheduled for two hours later was per a flight attendant that their requirements are twelve hours of break time, and various factors made it a bit tight prior to the flight.

Time changes also can occur as an adjustment to Daylight Savings Time, as the flight may be slotted in a slot restricted airport and the time does not change in that country or changes at a different time in the year.