Air accidents (like most accidents in complex human systems) are caused by a long series of problems, mistakes, missed opportunities, and other glitches that linked together like a chain, set up the potential for a tragedy long before someone came along and added the final link.

The Comair crash is no exception.

There are, in fact, many things that can contribute to a professional airline pilot starting down the wrong ribbon of concrete.

Whether confused by a forest of sometimes conflicting runway signs, hurried along by pressures of schedule and other aircraft, or victimized by your own assumptions of where you are in a complex airport, most experienced pilots have done something similar at least a few times in their careers, me included.

In fact, I can recall three instances in 13,000 hours of professional flying when my airplane ended up on the wrong runway. Fortunately, in each instance, we (or the tower) caught it in time.

When it's as dark at an airport as it was on Sunday morning when Comair 5191 left its gate, the visual clues and markings on taxiways become significantly more difficult to read.

Runways and landmarks that are so easily seen during the day may literally disappear at night, leaving the pilots with a combination of their own internal compass supplemented by taxiway lights and whatever lighted signs loom at them carrying the numbers of runways and taxiways alike.

And Sunday, there may have been an added problem created by the airport work crews changing the markings leading toward the main runway, though it's much too early to know if that was a factor.

But it gets more complex.