According to ABC News:
"Continental led the pack with 58 deaths, injuries or lost pets between May 2005 through December 2009, according to the DOT. It was followed by Delta (including now merged Northwest) with 43 incidents, Alaska Airlines at 36, American Airlines at 33 and United at 17... Then there is US Airways. That airline flies 44 million people a year domestically but only lost, injured or killed three dogs past four-and-a-half years."
Reports also show that short-snouted dogs such as bulldogs are more susceptible to injury and death during transport. And dogs are usually housed in areas that can become cold during the winter months.
Our advice? Limit your dog's flying as much as possible; it's better safe than sorry!