Basically, the whole subject of instrument procedure design can be summed up in two words: „Safety and Tolerance“
An IFP (or „instrument approach“) is the method by which pilots are able to position and then land an aircraft safely in reduced visibility or to achieve conditions under which visual navigation can be undertaken, permitting a safe visual landing to be made. Approaches are classified as either precision or non-precision, depending on the accuracy and capabilities of the navigational aids (navaids) used. Precision approaches utilize both lateral and vertical guidance information. Non-precision approaches provide lateral course information only. Similar procedures exist by which pilots are able to fly safe, accurate departure profiles from airports as well.
The publications depicting IFPs graphically show the specific procedure to be followed by a pilot for a particular type of approach to a given runway. They detail prescribed altitudes and headings to be flown, as well as obstacles, terrain, and potentially conflicting airspace. In addition, they also list missed approach procedures and commonly-used radio frequencies. As may be imagined, the production of these IFPs result from the application of extremely detailed safety criteria and an iterative process that requires the application of powerful and very sophisticated computer software programs to realize the most operationally effective and, above all else, safe result.