From mid-2009, the airport was served by 9 airlines flying regular flight service, of which KLM had the busiest route with over 200,000 annual passengers to Amsterdam Schiphol. In 2011, Ryanair announced that Billund Airport with effect from 25 March 2012 would be the base for two Boeing 737 aircraft. At the same time Ryanair published 5 new routes, so that, from the summer of 2012, they would fly to 19 destinations.
The first few bags build the small truck with carts that you see on airport runways. The truck has a "follow me" sign that I confess I have not seen at any airport. There is also a fueling tank and a rolling staircase that sits next to the plane to allow for boarding. Both the tank and the staircase are additional carts for the truck, though I am guessing not both at the same time.
The upper and lower wings are connected by a dark bluish grey 4 x 1 x 3 tail on either side; this tail element is unique to the set in this colour, although has previously appeared in a couple of sets back in 2003 in old dark grey. The upper wing is also supported by a couple of 1 x 2 x 2 black windows placed back to back in front of the cockpit, which from the perspective of the pilot really can’t be good for visibility. The biplane has a three blade propeller and the tips of the blades are stickered prior to sliding the propeller on to a 6L axle protruding from the front of the fuselage where it’s held in place by an orange 2 x 2 brick with domed top. The last step is to attach a 1 x 4 x 2 bar to the top of the upper wing for the Wing Walker to hold on to and then we’re done with the biplane.

City is the thematic title under which most Town-related System sets were released from 2005 and onward. There are numerous sets that are associated with Construction, Police, Fire, Emergency, Train, Airport, Transportation, Cargo, Traffic, Coast Guard, Farm, Great Vehicles, Mining, and Space. European catalogs featured another theme called City in the years 1999 to 2000, which was referred to as City Center in American catalogs.

Bag 4 finishes the fuselage and all that is left are the engines and tail section.  You'll notice that this aircraft has a bathroom on board as well as some storage for a non-existent flight attendant.  I think this is the first time that LEGO has put some additional details into aircraft besides just seats.  Also there is only one pilot for a 2 seat cockpit in the set.  
The remainder of the build is the control tower and terminal building. First there is a metal detector screener leading to the waiting/secure area of the airport, which seems taller than it needs to be for the minifigures. I think the same effect could have been made with half the height, except that would not allow for an impressive height for the overall tower. However it does seem to be similar to many modern airports with the high ceilings. This area also seems to be someplace to check luggage as evidenced by the rather nifty conveyor belt that comes in a full part. The moving parts of the set include a revolving door (a very tall one, for the first floor) that leads from the secure area of the airport out to the tarmac, and of course the conveyor belt.