For instance, the survey showed the Delta and United mobile and app views, respectively, of a seating chart, which seemed potentially difficult to use, but noted "there is no screen shot for Southwest because they don't have a seat map."

Delta spokesman Paul Skrbec said Delta launched its app in 2011 and focused on responding to the needs of a passenger who is in the airport. These include producing a boarding pass, looking for a gate or checking baggage. Delta later added additional features including bag tracking -- which currently is used by 6,000 passengers a day. In January, Delta added the ability to purchase tickets.

About 6.5 million people have downloaded the Fly Delta app on iPhone, Android, Blackberry, Windows and tablets. Delta builds its apps specifically for each device, Skrbec said. As a result, because Apple's iPhone has a particularly good camera function, the Delta iPhone app enables a passenger to track a bag's location after taking a picture of a baggage claim receipt.

American also has an app on every major platform and said it has had 7 million downloads across all major platforms.

-- Written by Ted Reed in Charlotte, N.C.

>To contact the writer of this article, click here: Ted Reed

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