CHICAGO — The United Airlines jumbo jet was on the ground at O'Hare International Airport after a flight from Hong Kong, looking as bedraggled as you would imagine, having been inhabited for 13 hours by hundreds of people crammed into close quarters.

Cleaning crews were on the job, but Paul Sanders leaned into a freshly sanitized lavatory, sniffing loudly, his head tilted back for full nasal intake. Beneath a blast of floral-scented disinfectant, he picked up a faint foul odor.

"I'm just not pleased with this bathroom," declared Sanders, eyeing the seemingly spotless lavatory. "Lucy! Lucy!" he bellowed to the supervisor in charge.

If only it had always been this way for the airline industry: a fastidious United manager like Sanders, nicknamed Mr. Clean, charged with ensuring that the glamour of flying was regularly scrubbed and spritzed back into the fleet.

For much of this decade, that had not been the case. Along with flight delays, passengers trapped onboard U.S. airlines were forced to sit amid other people's filth: crumbs, coffee stains, dirty Kleenex in seatback pockets and often far worse detritus in bathrooms as carriers skimped on cleaning to save money.

Anyone who logs a lot of air miles has stories. For Chicago financial manager Linda Ransford, it was the time she inadvertently set a brand-new handbag in a puddle of orange juice under her seat.

But airlines now are cleaning up their act and their planes as passengers travel less and become more sought-after customers due to the recession, finally acknowledging gaping service shortfalls that have made flying in the U.S. such a misery in recent years.

Among them, United Airlines is starting to pay greater attention to its planes, after scoring last in a J.D. Power and Associates survey of airline customer service in 2008 and tying with Northwest Airlines for the lowest consumer ranking of its aircraft interiors.

Starting last fall at Chicago's O'Hare, United overhauled both how it tackles dirt and stains on its jets and how often it does so, a process it has since rolled out to 13 other cities.

American Airlines has seen passenger complaints about dirty planes fall by 40 percent since it stepped up its cleaning last year, said spokesman Tim Smith.

At a time when airlines are scrambling to attract passengers, ridding an aircraft cabin of grime is a business necessity. Cleanliness "absolutely" affects passenger loyalty, said Jack Smith, senior vice president for customer service with AirTran Airways. "People don't normally return to a restaurant if they think it's dirty."

Getting an airplane spick-and-span is more difficult than it might seem, however. Carriers like United can't use common household cleaning agents like bleach and ammonia, which might damage a plane's aluminum frame. Fearing corrosion, they also can't hose down galleys, where food is prepared, like restaurants would kitchens.

Then there's the hobgoblin of inconsistency, getting crews on different continents to use cleaning materials correctly and to scrub to the new, higher standard dictated from United's Chicago headquarters. Schedules are always tight.

United used to let each of its airports determine how planes would be cleaned. Now, headquarters sets the tone and the standards, using a process that is broken into simple steps with clear goals that crews can follow, no matter where they are based.

"We want to make sure we use each cleaning agent in the right place, use the right wipes in the right place," said Sanders, whom United hired last year as general manager for cabin appearance. "The last thing we want is for someone to wipe the (lavatories), then use the same wipe on tray tables."

The main reason why United's planes lagged other carriers was because they were cleaned far less frequently than the industry standard, a practice the nation's third-largest carrier adopted during its bankruptcy, when it was conserving cash to survive.

United's aircraft typically would languish for six months between "heavy" cleans, and sometimes as long as every 18 months. That is an intensive scrubbing of the passenger cabin, done every 30 days at many carriers .

Now, the intensive cleans are done every 30 days for the smaller United jets that fly within the U.S. and every 15 days for the wide-body aircraft that cross the Atlantic and Pacific Oceans, enduring wear and tear during long flights that cause planes to become run-down more quickly.

All 409 of United's planes have undergone deep cleaning since the fall, and the aircraft are starting to shed the patina of grime that built up over years of neglect.

United says its internal survey data show that passenger ratings of cabin cleanliness have increased sixfold since September. But that's not good enough for Timothy Canavan, the former Delta Air Lines executive hired last summer to shake up United's maintenance and clean up its aircraft.

"It will take four to five heavy cleans before I can go on an aircraft and say, 'Yes, we're getting there,' " Canavan said.

Every time he boards a United flight, Canavan said he checks the entryway for stains, paces the cabin looking for frayed carpet, dirty overhead bins, unsavory-smelling bathrooms and the like. He introduces himself to the crew and asks them to point out problem areas. "Then I sit in my seat and start firing off e-mails."

But some jaded travelers question whether old-line carriers, who remain under intense pressure to control costs, are treating cosmetic issues like dirt on planes because doing so is cheaper than remedying underlying service problems like understaffing crews, ticket counters and lost-baggage centers.

"You ask people to rate the planes, they notice dirty," said Joe Brancatelli, travel writer and publisher of Web site Joe Sent Me (www.joesentme.com). "They assume late; they notice dirty."