Cometari have started working on the RESTFull API which allow user to find the nearest airport based on give GEO location. API will be released soon and available for each user for free.
Whenever you are building travel application you need to implement features which gives you the nearest airport for given search criteria such as city. The lack of free API was covered by Cometari and gives all developers possibilites to add feature – find the nearest airport – to their tailored travel applications.
More detailes you can find at product page for Airport Finder API.