Originally Posted by HDQDD

Yes and No. Short answer: Airlines don't cancel flights (esp Int'l) simply because loads are light. It causes too much disruption to their schedule. However, if operational problems arise, one of the things considered is pax impact.

Long answer: Every airline system ops control center has a person or persons who "route" airplanes. The company I worked for simply called this person a "router". I was this person for a while. The router decides (using lots of computer models) which airplanes fly which flights. Some of this is done weeks in advance, some is done days in advance, and some is done on the fly to react to operational issues. There are a ton of things a router has to consider to do their job. Maintenance (MX) and crew routing are most important. Passengers are too, but lower on the list of priorities.

I won't bore everyone with the details of routing, but I will say that there are days that a router comes to work to find out that: "We're short 4 737-700's @ATL today due to maintenance, bird strike, lightning strike, etc." Then the router has gaps to fill in the days flight operations. There are a few ways to handle this. Start delaying lines of flight to pickup the slack, or start axing flights. But it's not that easy. Certain airplanes have to be in certain cities for planned overnight maintenance (most important), you have to consider a crew's line of flight to make sure you don't break their 4 day schedule. Then passengers are considered. If it makes sense to cancel a few rounds (i.e. out and backs, like ATL-LGA-ATL), you do it. Example: If ATL-LGA-ATL is lightly booked and pax can easily be accommodated on other flights, AND the crew was supposed to do ATL-LGA-ATL (so they can resume their flight line) then that may be an easy choice. To sweeten the pot, LGA just happens to be on a GDP (Ground Delay Program) you cancel and sub, and now you can perhaps put all the other LGA flights ontime (or at least reduce their EDCT's).

So the answer is yes, sometimes airlines do cancel lightly booked flights when they are forced to "prune" the schedule for operational reasons. But they don't cancel solely for that reason. It's too disruptive to their sensitive schedule. Especially with Int'l flights. Most of your TATL flights the crew spends 2-3 nights at their destination before flying the airplane back. It gets expensive quick when you break those pairings.

Not to mention the DOT publishes airlines completion percentages (although that's only for domestic flights).