Ramon
There could be several other factors however here's a quick hit finding:
1. Inbound Link anchor text spread
While you've got much more content and many more links, wholesale-flights.com has a much broader variety of inbound link anchor text related to "business class" than you do, including pointing to their home page. (OpenSiteExplorer.org is great for providing insights like this).
2. Internal keyword saturation
You've got an extremely over-saturated usage of keywords in your internal linking (all those links in the bottom third of your home page for example)
By not having enough inbound link quality relative to that specific phrase, and simultaneously having too much use on internal links, you're out of balance.
3. Core architecture flaw
When I go to your Business Class page, the entire top navigation is gone. As though you've made that specific page into more of a PPC landing page than a primary site page.
On that Business Class page, you've got section level navigation specific to Business class, with the top link labeled "home". Again, this communicates that this really isn't a core part of the main site, but some sort of isolated section. This then isolates this section improperly. Then on one of those sub-pages, not only are the top navigation links gone, so are the primary site footer links.
Yes, it's good, and important to maintain that section level navigation, yet it's just as important to communicate that it's a core section of the main site.
4. Section level content.
Other than the initial business class page, none of the other pages in that section have any substantial content to speak of - they're all very weak overall.