Passenger yield (Passenger Revenue per Revenue Passenger Mile) for American has decreased slightly in recent years due to competition from low-cost airlines and poor domestic economic conditions.

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Domestic Passenger yield (passenger revenue per revenue passenger mile) for UAL has decreased slightly in recent years due to competition from low-cost airlines and poor domestic economic conditions.

FORBES: United Continental Has Upside To $28 Despite Low-Price Threat

In the meantime, the number that really matters--called the "yield, " or the price a passenger pays to fly one mile--fell 4.5%.

FORBES: Frontier Airlines Braces For Turbulence

If yield levels do not fall, which is likely as passenger fares were stable, then we will see impressive top line growth in the fourth quarter.

FORBES: Alaska's Earnings Will Get A Tailwind From Higher Capacity & Passenger Traffic

Southwest, which doesn't charge fees for a passenger's first two checked bags, pushed its prices up faster than its competitors: Its yield jumped 35% over the same period.

WSJ: Where Airfares Are Taking Off