fix (FAF) altitude on NPAs while a lightning bolt does the same for PAs. NPAs depict the MDA while a PA shows both the decision altitude (DA) and decision height (DH). Finally, the chart depicts the missed approach procedures in plan and profile view, besides listing the steps in sequence. Before satellite navigation (GNSS) was available for civilian aviation, the requirement for large land-based navigation aid (NAVAID) facilities generally limited the use of instrument approaches to land-based (i.e. asphalt, gravel, turf, ice) runways (and those on aircraft carriers). GNSS technology allows, at least theoretically, to create instrument approaches to any point on the Earth's surface (whether on land or water); consequently, there are nowadays examples of water aerodromes (such as Rangeley Lake Seaplane Base in Maine, United States) that have GNSS-based approaches. Instrument approach segments An instrument approach procedure may contain up to five separate segments, which depict course, distance, and minimum altitude. These segments are Feeder routes: A route for aircraft to proceed from the en route structure to the IAF, which includes the course and bearing to be flown, the distance, and the minimum altitude. Initial approach segment: This segment provides a method for aligning the aircraft with the intermediate or final approach segment and to permit descent during the alignment. It begins at an IAF and ends at the intermediate approach segment or intermediate fix (IF). A DME arc, a procedure turn / teardrop turn, or holding pattern may be involved or the terminal route may simply intersect the final approach course. Intermediate approach segment: This segment positions the aircraft for the final descent to the airport. It begins at the IF and ends at the final approach segment. Final approach segment: For a PA or APV, this segment starts where the glideslope intercepts the glideslope-intercept altitude plane. For an NPA, this segment starts at the FAF, final approach point (FAP), or where the aircraft is established on the final approach course. This segment ends at either the designated missed approach point (MAP) or upon landing. Missed approach segment: This segment starts at the MAP and ends at a point or fix where the initial or en route segment begins. When an aircraft is under radar control, air traffic control (ATC) may replace some or all of these phases of the approach with radar vectors (ICAO radar vectoring is the provision of navigational guidance to aircraft in