What does the small fan do that is visible on Boeing 787 Dreamliners on landing? When watching landing videos of 787's that are in service I've been noticing a fan that is located under the right rear section of the fuselage.  I've now seen it on 4 different 787's  from 4 different airlines.  

Is this an emergency fan that's deploying, or is it just something that's designed to recharge some of the batteries on board?  Some auxiliary type of system, perhaps?
If you are speaking of the small fan behind the gear in the photo below (click to magnify)


Image from here.

you are speaking of a Ram Air Turbine, usually used in an emergency, not in normal operations.