NEW YORK (CNN/Money) - After a summer of full airplanes and higher fares, airlines are preparing to cut prices again to keep up demand through the fall travel season.

Wednesday industry leader American Airlines announced a new round of fare sales, with some fares as low as $49 one-way.

The cuts follow moves last week by some leading discount carriers, including Southwest Airlines, which had some transcontinental fares as low as $99 one-way. That fare then was matched by some major carriers, such as United Airlines, which disclosed its fall sales plans Monday, including both discounted air fares and hotel stays.

"This is the first week we've had for a while where you can walk away feeling you have a rock-bottom deal," said Tom Parsons, president of Bestfares.com, who said the lowest prices were about $150 more round-trip on a trans-continental flight through most of the summer.

Fall fare sales are nothing new in the industry -- they're the norm even in good times for airlines as the peak summer travel season comes to an end. But the current fare sale comes as the industry struggles for improved returns from customers even when planes are close to full.

"What you have to remember is average fares are at 20-year lows," American Airlines spokesman Tim Wagner said. "When you run a fare sale off 20-year lows, you get fantastic fares."

The airlines all reported a historically high percentage of seats filled through June and July, a measure known as load factor that compares miles flown by paying passengers with the potential capacity of an airline.

Since many major carriers like American and United cut capacity this summer due to weak economics, both the money-losing major carriers and the profitable discount carriers like Southwest and JetBlue generally were reporting record or near-record load factors. That made it tough to find the real rock-bottom fares seen earlier the year, Parsons said.

But overall fares as measured by the average amount paid by passengers per mile flown have not shown much, if any, improvement, according to industry analysts, as the growth of discount airlines forced the major carriers to keep top fares low.

"The load factors are unprecedented, and in a pre-9/11 environment, this would clearly be a boon to (higher fares)," said John Heimlich, managing director of economics for the Air Transport Association, the industry trade group. "With the way things are, we are only getting a modest (fare) benefit."

The pressure on more expensive business fares is only set to increase with continue growth of discounters in key markets, such as cross-country flights.

America West Airlines announced Monday it will start its first non-stop transcontinental service between New York's Kennedy International Airport and Boston Logan International Airport, on the East Coast, and Los Angeles International Airport and San Francisco International Airport on the West Coast, with some flights coming as soon as October.

That is more good news to cross-country travelers, as it's likely to prompt the large airlines to continue cutting fares on these key routes, Lehman Brothers airline analyst Gary Chase said. He estimated in a note to clients that these routes produced $1.3 billion a year in revenue for the four largest airlines serving those markets -- American, United, Delta Air Lines and Continental Airlines.

"These transcontinental markets have been flagship business routes for the airlines and in better times were large profit generators," Chase wrote. "America West's entry into these markets, however, begs the question of whether or not these routes will be large profit generators in any up cycle, especially if the network airlines are forced to match America West's fare structure."