Research the following airlines and discuss the commonalities between all of them. Additionally, discuss the differences or what makes them unique compared to other airlines within the industry. Discuss this from an operational perspective (route structure, aircraft, cost structure, etc.) AND from a service perspective (airport and onboard services or amenities, customer perceptions, etc.) :

a. Ryan Air (Europe)

b. JetBlue (U.S.)

c. Singapore Airlines (Singapore)

d. Porter Airlines (Canada)