United Airlines' Tech Meltdown -- It Could Happen Again

June 21, 2007 — -- What happened to United Airlines on Wednesday has happened before to other large carriers, and it will happen again — the unexpected shutdown of a computer system that has become so integral to the airline's operations that planes simply can't fly without it.

In Wednesday's case, it was United's turn to experience a sudden inability to compute the weight and balance figures (and other performance data) for each outbound flight, and that inability struck at the heart of the airline's schedule.

Each airline designs its own system for tracking and figuring the amount of weight on an outbound flight. Decades back, all airlines calculated such items with pencil and paper, but today computers do the work. For most big airlines, the computer systems are centralized — United's is in the Chicago area; American's is near Tulsa, Okla., etc.

But the problem is that once the Federal Aviation Administration approves the way that computer system is used by an airline for such critical functions as weight and balance, the system has to work to run the airline. If it stops working, no flights can fly until it either comes back on line or the airline goes to some approved backup system for manual calculation. In the meantime, as little as a half-hour delay can throw the system into chaos.

Today's big airlines and airports both operate like an intricate Swiss watch: As long as everything functions reasonably close to the way it's been designed, the whole mechanism can self-correct for minor deviations. But throw sand in the delicate gears — or a multihour delay in launching hundreds of flights — and the mechanism begins to break down rapidly.

Perhaps the most basic problem is just gate space. In a major so-called hub airport, such as Chicago's O'Hare, arriving flights are scheduled into gates mere minutes after departing flights are scheduled to push back. Obviously, when the outbound aircraft doesn't leave the gate, an inbound flight is orphaned.