Airfare continues to drop after steep July decline

A United Airlines jet passes the air traffic control tower at Los Angeles International Airport.
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There's good news on the horizon for air travelers.

Major airline fares fell by 3.1 percent in August, according to the Bureau of Labor Statistics. This comes after a 5.6 percent drop in the index in July, which was the steepest monthly decline in airline fares in 20 years.

Seth Kaplan, managing partner of Airline Weekly, told CNBC that this second drop in fares doesn't surprise him at all.

"Airlines are still growing their capacity, their supply of seats, more rapidly than the U.S. economy is growing," he said.

Kaplan cited historically low oil prices as the reason for the consecutive drop in airfare and said it's all about simple supply and demand economics.

"[Airlines] are trying to find that sweet spot where the unit cost is falling faster than the revenues."

Kaplan said they're doing this by hiring new workers at the bottom of the wage scale and flying airplanes more hours per day, something airlines couldn't necessarily worry about when fuel prices were higher.

"It's a pretty good scenario for airlines and consumers alike," Kaplan said.

Read More Airfares see sharpest monthly decline in 20 years

But what does Thursday's impending Fed decision mean for consumers?

"If the price of oil, thus, jet fuel, falls as the result of a Fed move, it's not that airlines would immediately pass the lower cost through consumers," Kaplan said. "But if they feel confident that jet fuel is going to remain cheap for the foreseeable future, then they're more likely to remain growing."

Kaplan said growing airlines lead to additional seats and therefore more downward pressure on airfare throughout the rest of the year.

However, that doesn't mean passengers should necessarily buy now for the best prices on upcoming holiday travel.

"When consumers think about holiday travel purchases, they shouldn't think about it terms much different than they did in the past," he advised.

Passengers can generally get the best deal about a month before they travel and if they buy too far in advance they won't always get the best rate. Kaplan said on average, relative to last year's rates, consumers will be paying less but rates won't automatically be cheaper tomorrow than they are today.

Despite the deceleration, Kaplan said one notion always stands true: "You can find a deal if you're willing to be creative."

Airfares drop sharply