When is a flight too empty to fly?

A few years ago I was scheduled to fly from New York to London on the first of American Airlines' three nightly departures. As the departure time came and went it became clear something was wrong. Soon enough, my flight was cancelled, and all of the passengers were jammed onto the second flight, which left two hours later. Many of us missed connecting flights at Heathrow, and my Swiss vacation got off to a rocky start.

The airline never gave a clear reason why my flight was cancelled, but I suspected they just didn't feel like flying two half-empty planes when they could fly one full one. Obviously I felt at the time that both flights should fly, but in retrospect, isn't that a rather un-green way of thinking?

The issue boiled up recently when it was reported that American flew a huge Boeing 777 from Chicago to London in February with only five passengers aboard. According to reports, the five people were leftover from a flight that had been cancelled earlier in the day, and the airline felt obligated to get them to London and to get the plane where it needed to be to bring another load of people back from Europe on time.

That all makes a certain sense, but still, what about the 22,000 gallons of jet fuel burned in the process (creating 43 tons of C02 per person)?

Could it be that I actually feel a little sorry for American Airlines? Thrust into a no-win situation, it erred on the side of customer service and scheduling at the expense of the environment. From the comfort of my home I feel it was a mistake, but if I had been one of those five passengers stuck at O'Hare, you can be sure I would have been eager for that plane to fly.