Just months after Delta began installing new interiors, including pricey leather seats, Mr. Canavan and his staff were surprised to find that some of the planes were already filthy. Thus began a humbling airlinewide effort to become neater.

Two cleaning contractors were fired for slipshod performance. Deep cleaning  an intense and precisely scripted process of brushing, scrubbing and vacuuming  now occurs at least every 30 days on Delta planes, bringing Delta up to par. A crew of auditors checks up on the cleaners.

Delta is not the only airline paying closer attention to the issue since 9/11, when any number of niceties  as well as basics  were scrapped. More recently, bloggers, flight attendants and others have been taking note of filthy and fragrant conditions on planes; it is not clear how much of a difference some of the carriers’ galvanized housekeeping efforts have made.

“There’s still a long ways they have to go,” said Linda Hirneise, who heads the travel practice at J. D. Power & Associates, a market research firm. Her company surveys passengers about airline cleanliness, and this year the top-ranked carrier  JetBlue  received an 8.49 on a 10-point scale.

But in Ms. Hirneise’s opinion, “anything below a nine is flunking.”

Delta came in third in this year’s J. D. Power survey, behind JetBlue and Southwest. At the bottom of the survey, which ranked only North American airlines, were Northwest and US Airways.

“All carriers have room for improvement,” Ms. Hirneise said. “Sometimes you pull those trays down and you just want to walk off the plane.”

The Federal Aviation Administration does not set cleanliness standards, so the issue is mainly one of public perception.