Tales of sweaty waits on un-air-conditioned planes, smelly bathrooms, dirty seats and tray-tables smeared with mysterious schmutz abound this season. Travelers complain that the environment on packed planes can degenerate quickly - and often long before the plane actually starts moving.

''When you get off a plane, it looks like the morning after a fraternity house party,'' says Tim Winship, publisher of FrequentFlier.com, a Web site that offers frequent-flier program information and advice.

Airlines say they are not skimping on cleaning procedures, but horror stories are plentiful. One of the most high-profile this summer was a trans-Atlantic Continental Airlines flight in June, on which sewage overflowed from a lavatory and spilled down the aisle. ''It smelled like an outhouse,'' says Dana Bushman, who was on the flight. Continental later apologized and offered vouchers to the passengers, but Bushman says she is trying to gather support from fellow passengers to sue the carrier. Continental said it determined that the blockage was caused by someone attempting to flush latex gloves.

Delays can affect cleanliness and comfort, particularly with planes now flying fuller. The percentage of on-time flights fell to 74.5 percent in July from 76.4 percent a year earlier, according to FlightStats.com. Summer thunderstorms get some of the blame, as do technical glitches such as the Federal Aviation Administration computer meltdown on June 8.

Because of delays and rebookings, planes can remain in circulation past their scheduled cleaning, says Judy Graham-Weaver, a spokeswoman for AirTran Airways, a division of AirTran Holdings Inc.

Still, the airlines say their schedules for cleaning aircraft haven't changed this summer despite the rampant delays. JetBlue Airways Corp. says its planes undergo a ''maximum deep clean'' once a month, same as before, a process that includes a thorough cleaning of the lavatories and galleys, vacuuming of carpets and cleaning of seats, seat trays and side walls.

Southwest Airlines Co. and Delta Air Lines say their deep-cleaning cycle is 30 days, too. American Airlines says it also keeps a 30-day average. Continental Airlines Inc., like many airlines, says its planes also undergo an overnight cleaning, which includes replacement of soiled pillows and blankets, vacuuming of cabin floors and cleaning of lavatories and passenger seating areas.

Between flights, though, the cleaning tends to be cursory. American says that it picks up trash and cleans seat-back pouches between flights, but that it doesn't wipe down tray tables or vacuum while at the gate unless there's an obvious mess that must be addressed.

Cleaning schedules and corporate policies don't seem to be enough to allay customer concerns. American says it's in the process of refurbishing many of its aircraft, having found that customers perceive worn interiors to be unclean, even if they're actually spic-and-span.

Airplane lavatories have been gaining increased attention because of widely publicized stories such as the Continental flight and more common breakdowns, such as on Jack Wolf's Northwest Airlines flight from Minneapolis to New Orleans on July 20. One of the two coach lavatories was inoperative, leaving one lavatory for all of the coach passengers. There was also one in first class, but Wolf says that an announcement was made reminding coach passengers to use only the lavatory in their cabin.

Northwest acknowledges that a lavatory was inoperative, that maintenance looked at it before departure and that it was determined that flying with two of three lavatories working (including the one in first class) was preferable to delaying the flight for repairs or an aircraft change.