"Allegiant has one of the oldest and most fuel-inefficient fleets in the airline industry, " said Vaughn Cordle, an analyst with AirlineForecasts.

CNN: Allegiant Air adds carry-on fee

For a tiny carrier like Samoa Air, the fare model seems reasonable, according to airline analyst Vaughn Cordle, a partner at Ionosphere Capital.

CNN: Pay-as-you-weigh airfares the 'next step'

Aviation analyst Vaughn Cordle of AirlineForecasts tipped mobile connectivity to become standard across the industry, and the price of access to drop.

CNN: In-flight phone calls to become standard, say experts

An ultra-low-fare model gives carriers such as Allegiant and Spirit more flexibility in unbundling the costs of air travel, Cordle said, but other airlines will be watching the carry-on fee closely.

CNN: Allegiant Air adds carry-on fee

"They're all trying to move that route, but it's a little harder for the higher-cost network airlines to tack on higher fees associated with getting passengers from A to B, " Cordle said.

CNN: Allegiant Air adds carry-on fee

"US Airway (currently) loses money on that short segment, but if they can carry that passenger to another major hub or fly them internationally, they capture that incremental revenue, " says Vaughn Cordle, an airline analyst and co-founder of Ionosphere Capital.

WSJ: Little overlap in American, US Airways routes