sentences:  Chapter 4 of Annex 14 to the Convention on International Civil Aviation "[establishes] a series of obstacle limitation surfaces that define the limits to which objects may project into the airspace" surrounding an aerodrome.PANS-OPS defines "protection surfaces" which are imaginary surfaces in space that guarantee an aircraft a certain minimum obstacle clearance, similar to the purpose of obstacle limitation surfaces (OLS) in Annex 14.These surfaces may be used as a tool for local governments in assessing building development.