According to the AIM [5-4-1], “A SURVEILLANCE APPROACH (ASR) is one in which a controller provides navigational guidance in azimuth only. The pilot is furnished headings to fly to align the aircraft with the extended centerline of the landing runway. Since the radar information used for a surveillance approach is considerably less precise than that used for a precision approach, the accuracy of the approach will not be as great and higher minimums will apply.”
If requested by the pilot, recommended altitudes will be issued at each mile, based on the descent gradient established for the procedure, down to the last mile.
The controller continues the vectors to keep the aircraft on course until the pilot can complete the approach and landing by visual reference to the surface.
Here’s an an example of an ASR approach into Dane County Regional Airport in Minnesota, watch the video here.
Note: This type of approach is currently not available in Infinite Flight.