Why do so many passengers get off the plane only to discover that their baggage did not make the trip with them?
American Airlines started asking that question with greater urgency a year ago, and its search for answers led to, among other problems, dirty printer heads.
Workers at American found that printers that produce adhesive tags for bags were often dirty. That made bar codes hard to read, leading to misdirected bags. Regular wiping of the printer heads helped, but even with a clean printer, the bar code readers are only about 90 percent to 92 percent accurate, said Denise Wilewski, manager of airport services for American here.
''We never hit 100 percent - 90 percent is acceptable,'' she said.
Airlines are fond of saying that they have a success rate of more than 99 percent in getting luggage to its destination along with its owner. And every big airline has stepped up efforts to improve its operations.
But the baggage problem is getting worse. One in every 138 checked bags was lost during the first nine months of this year, compared with one in 155 bags a year earlier.
The Thanksgiving holiday, which is on Thursday, is already shaping up as a difficult travel time with storms moving across the United States from the Northwest.
And by the end of the year, close to five million travelers will have been frustrated at the luggage carousel.
Toby Sherman is one of them. Traveling with his wife and their 7-year-old triplets last weekend, Sherman, who lives in Huntington Beach, California, checked five bags with American Airlines at John Wayne Airport, in Orange County.
But just four bags showed up in Chicago, where the Shermans had come to spend Thanksgiving with family.
One son's clothes were in the missing bag, said Sherman, who was planning a trip to the mall to buy some replacements. ''Never a dull moment,'' he said.
Holiday travelers can expect to feel the effects of six years of airline downsizing in one way or another. About 27 million passengers are expected to fly during the 12 days surrounding Thanksgiving, 4 percent more than last year, the Air Transport Association said.
But there are fewer airline employees to look after them, and their bags. And to squeeze more flights out of the day, planes are sitting on the ground for shorter periods between flights. So, predictably, more bags fail to join their owners, particularly on connecting flights.
''There's a lot of opportunity for failure,'' said Hans Hauck, manager of baggage operations at American's headquarters in Fort Worth, Texas.
Since Hauck started his job in September 2006, American has not met its bag-handling goal in any month. As of late last week, though, Hauck remained hopeful that he would make his November number.
A look at American's bag-handling operation, the biggest of all U.S. carriers, shows that it is making lots of little improvements but still losing ground. American misplaced 7.44 bags for every 1,000 through Sept. 30, the Bureau of Transportation Statistics reported, up from 6.04 a year earlier.
All but a tiny fraction of misplaced bags are ultimately reunited with their owners.
All the other big carriers have worse records so far this year, too. US Airways continues to struggle with bag handling at its Philadelphia hub, three years and more than $12 million in improvements after a Christmas 2004 meltdown. And Delta Air Lines is trying to improve bag handling at its big Atlanta hub.
Except for a canceled flight, nothing quite disrupts a trip like a lost bag. Mike Laitman of La Grange Park, a Chicago suburb, bought circus tickets for relatives arriving from Missoula, Montana, last Saturday. Their wait for a missing bag kept them all at O'Hare International Airport so long that they missed the show. Baggage representatives for Alaska Airlines ''told us to keep waiting,'' Laitman said, watching his nephew ride the baggage carousel. ''We're out $70.''
Lost baggage is actually a worse problem than reflected in the big airlines' statistics. Regional airlines misplace bags at a higher rate. But they report their statistics separately, even though many passengers travel on these regional airlines for just one leg of their trip.
Counting together American and the regional airline it owns, American Eagle, mishandled bags grow to 8.69 per 1,000, or a total of 639,146 through Sept. 30.
American Eagle had the worst bag-handling record of 20 airlines tracked by the Bureau of Transportation Statistics during that period, the agency reported.
American's baggage operation at O'Hare, the airline's second largest hub, is massive, with more than seven miles, or 11 kilometers, of conveyers, hundreds of workers and scores of tractors pulling baggage carts.
Checked bags are immediately sent on a fast conveyer to be screened by the Transportation Security Administration and then sent back to American's big bag room. There, bar-code readers direct the bags onto piers that handle one or more destinations. From there, bags are placed on carts and towed out to planes for loading.
Bags with unreadable tags are left to circle the piers up to three times before being hauled off and manually placed in the correct stack.
About 2 percent are misread and dropped onto the wrong pier. Then, it is up to a worker stacking the bags on carts to notice the mistake.
American and other domestic airlines have resisted investing in radio frequency identification tags, which are used by big retailers to track inventory and are far more accurate.
The tags cost about 20 cents each so it would cost $50,000 a day for American's 250,000 bags, plus the cost of hardware to read them at each step in the process.
''We don't lose enough bags to justify that investment,'' said Mark Mitchell, American's managing director of customer experience.
American's workers also stopped unloading entire planes in some instances in the last year, instead hauling off only bags that need to be rushed to connecting flights and then returning for the rest, said Wilewski, the baggage manager. Bags failing to make connections account for 60 percent of mishandled bags, American said.
In the months ahead, American also plans to install laptop computers on tractors that pull baggage carts so that workers know of last-minute gate changes, late arrivals and other complications. Drivers have long used written orders and often arrived at a gate to find the expected plane was not there.
American handles 20,000 to 35,000 checked bags a day in Chicago. Wilewski's goal for November is 7.95 mishandled bags for every 1,000. ''We're not to go above that,'' she said. ''We're under it right now.''
Her Chicago operation met its monthly goal for the first time in two years in May and then met it again in September and October.
So, last Thursday, when morning flights to London and Honolulu were both delayed by more than eight hours because of mechanical problems, her staff quickly rounded up bags that had already been checked, knowing some passengers would switch flights or perhaps cancel their trip altogether.
As some passengers were rebooked, workers tried to keep their bags with them.
Wilewski said they got nearly all the London bags on the correct flights, but ''we did miss maybe 15 bags on Hawaii'' in the confusion.