The summer travel season was good for major carriers, but great for low-cost carriers.

JetBlue

(JBLU) - Get Report

said Thursday that load factor, or the percentage of seats filled on every plane, came in at 91.6% for the month of August, up from the year-ago 90.5%. The company managed to fill a higher percentage of seats and post a 69.6% year-over-year traffic increase despite the fact that it boosted capacity by 67.6%.

America West

(AWA)

, another low-cost competitor, also announced performance results for August, saying yields were improving and that the load factor came in at 82.1%, up from the year-ago 78.8%. Revenue passenger miles, or traffic, came in at a record $2 billion, up 2.6% from year-ago levels, while capacity fell by 1.5% from last year.

The ability to boost traffic while simultaneously cutting capacity can be a sign of strength -- or a sign that airlines are using discount tickets to drive demand. But America West said that revenue was strong with yield, a key metric reflecting pricing power that airlines need to improve in order to return to profits, showing "significant increases" in August.

"We continued the trend of very strong revenue performance with significant increases in both yields and passenger loads last month. Our August yield improvement was our highest year-over-year increase in any month since March 1998," said Scott Kirby, executive vice president of sales and marketing for the company, in a release.

The news from JetBlue and America West comes one day after the major network carriers rallied on news that planes were packed during the month of August. Especially notable Wednesday was

Continental's

(CAL) - Get Report

announcement that passenger revenue per available seat mile was up between 4% and 5% in August, which means travelers have begun to pay more for tickets.

After rallying more than 4% Wednesday, the Amex airlines were down 0.8% in early going on Thursday, led lower by

Northwest Airlines

(NWAC)

, off 30 cents, or 2.9%, at $9.95. JetBlue was up 54 cents, or 0.9%, at $57.84, while America West was up 5 cents, or 0.5%, at $9.40.