Air 11" i7 2011 fans come on, never turn off
The fans are controlled by the System Management Controller (SMC).

The first thing to try when troubleshooting a fan issue is resetting that SMC. In fact, Apple says this:


  After performing normal troubleshooting, these symptoms may indicate
  that an SMC reset may be necessary: [...] The computer's fans run at high speed although the computer is
  not experiencing heavy usage and is properly ventilated.


Apple has directions for all models, but I'll excerpt how to do it on your MacBook Air:


  
  Shut down the computer.
  Plug in the MagSafe power adapter to a power source, connecting it to    the Mac if its not already connected.
  On the built-in keyboard, press the (left side) Shift-Control-Option    keys and the power button at the same time.
  Release all the keys and the power button at the same time.
  Press the power button to turn on the computer.
  


One other thing you can try is the app smcFanControl, which claims to allow you to exercise some degree of control over your computer's fans.

This is about all you can do as a consumer; if there is still a problem you will need to take your computer to an Apple Store.