An electronic back door to American Airlines was left open briefly last month, affording a few cyber-sleuths an unguarded glimpse of the internal workings of the Dallas-based carrier.

The internal American Web site cast light on the airline’s efforts to save money and its concerns about competition from rival Southwest Airlines.

Though the site, AAflightservice.com, is intended only for the airline’s employees, a glitch (since repaired) allowed the public access. The glitch was reported on FlyerTalk.com, and members instantly flooded in.

Among other things, the site noted how much revenue increased after American tightened its excess baggage allowance last November. The carrier now requires passengers to pay a $25 surcharge for bags heavier than 50 pounds.

“For the month of December 2005 we collected $264,000 in excess, overweight and oversized bag charges,” a newsletter addressed to a ground crew at one airport announced. “This is a 7 percent increase over December 2004!” It called the fees an “an important ingredient” to its success.

“It was a treasure trove of documents,” Ben Edelman, a graduate student at Harvard University told reporter and industry expert Christopher Elliott. Edelman told Elliott that he was drawn to the site because it offered answers to questions no one at the airline could definitively answer.