According to data released by the federal government- which apparently tracks stats for animals that die en route to destinations- more pets died on Delta last year than any other airline.
Thirty-five pets died in transit in 2011, and a stunning 19 of the dead pets met their maker on Delta flights. However, Delta notes that of all the airlines servicing the US, it carries more pets per capita due to pet-friendly policies. Only.02% of animals transported on flights do not survive, and the cause is mostly down to health issues encountered by the pets rather than any sort of calamity or mishandling.
AirTran and Southwest both do not carry pets in a plane's cargo hold, and all pet deaths in 2011 occurred while pets were in cargo holds. According to the Atlanta Journal-Constitution, Delta has changed policy regarding pet travel in 2011, banning certain breeds from their flights due to the high propensity of the animals to encounter trouble:
One of Delta's latest changes came in December, when it stopped accepting snub-nosed dogs or cats as checked items. Delta already had banned American, English and French bulldogs from flying. That came after a sharp increase in the number of animals that ran into trouble on Delta flights, particularly bulldogs, which are susceptible to respiratory problems.
"The loss of any pet is unacceptable to us. We are working to improve the processes and procedures to ensure that every pet arrives safely at its destination."