And if you're not willing to pony up the cash for Whitney or Frutiger, your computer probably already has Segoe on it, which is a broadly similar humanist sans serif commissioned by Microsoft for UI and branding purposes. (All three share a design goal for signage and readability - Segoe for onscreen text, Whitney for a museum's signs, and Frutiger for airport signage)

/type snob

If you're really curious, Delta publishes their brand guidelines on the web. The relevant section for typography is here: http://deltabrandcenter.com/howweloo...pography.shtml