Who thinks airline mergers are a good thing? Certainly the employees of the newly merged American Airlines and US Airways, who will receive bonuses when their employers reach certain goals over competing carriers. This will prove especially important in the near future, now that Southwest Airlines announced it will launch international service to destinations in the Caribbean this July. Surprisingly, however, passengers are the other beneficiaries of airline mergers, according to a new study. The theory goes that mergers reduce redundant routes that in turn are filled in by low-cost carriers. Mergers also encourage airlines to purchase and operate fuel-efficient aircraft, according to researchers.