Instrument approach

In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually. These approaches are approved in the European Union by EASA and the respective country authorities and in the United States by the FAA or the United States Department of Defense for the military. The ICAO defines an instrument approach as a series of predetermined maneuvers by reference to flight instruments with specific protection from obstacles from the initial approach fix, or where applicable, from the beginning of a defined arrival route to a point from which a landing can be completed and thereafter, if landing is not completed, to a position at which holding or enroute obstacle clearance criteria apply. In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually. These approaches are approved in the European Union by EASA and the respective country authorities and in the United States by the FAA or the United States Department of Defense for the military. The ICAO defines an instrument approach as a series of predetermined maneuvers by reference to flight instruments with specific protection from obstacles from the initial approach fix, or where applicable, from the beginning of a defined arrival route to a point from which a landing can be completed and thereafter, if landing is not completed, to a position at which holding or enroute obstacle clearance criteria apply. There are three categories of instrument approach procedures: precision approach (PA), approach with vertical guidance (APV), and non-precision approach (NPA). A precision approach uses a navigation system that provides course and glidepath guidance. Examples include precision approach radar (PAR), instrument landing system (ILS), and GBAS landing system (GLS). An approach with vertical guidance also uses a navigation system for course and glidepath deviation, just not to the same standards as a PA. Examples include baro-VNAV, localizer type directional aid (LDA) with glidepath, LNAV/VNAV and LPV. A non-precision approach uses a navigation system for course deviation but does not provide glidepath information. These approaches include VOR, NDB and LNAV. PAs and APVs are flown to a decision height/altitude (DH/DA), while non-precision approaches are flown to a minimum descent altitude (MDA).:757 IAP charts are aeronautical charts that portray the aeronautical data that is required to execute an instrument approach to an airport. Besides depicting topographic features, hazards and obstructions, they depict the procedures and airport diagram. Each procedure chart uses a specific type of electronic navigation system such as an NDB, TACAN, VOR, ILS/MLS and RNAV.:981–982 The chart name reflects the primary navigational aid (NAVAID), if there is more than one straight-in procedure or if it is just a circling-only procedure. A communication strip on the chart lists frequencies in the order they are used. Minimum, maximum and mandatory altitudes are depicted in addition to the minimum safe altitude (MSA) for emergencies. A cross depicts the final approach 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.:4-9,4-11,4-19,4-20,4-41 Before satellite navigation 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. An instrument approach procedure may contain up to five separate segments, which depict course, distance, and minimum altitude. These segments are:4-43,4-53 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 the form of specific headings, based on the use of radar).:1033 ATC will use an imaginary 'approach gate' when vectoring aircraft to the final approach course. This gate will be 1 nautical mile (NM) from the FAF and at least 5 NM from the landing threshold. Outside radar environments, the instrument approach starts at the IAF.:4-54,4-56 Though ground-based NAVAID approaches still exist, the FAA is transitioning to approaches which are satellite-based (RNAV). Additionally, in lieu of the published approach procedure, a flight may continue as an IFR flight to landing while increasing the efficiency of the arrival with either a contact or visual approach.:4-57 A visual approach is an ATC authorization for an aircraft on an IFR flight plan to proceed visually to the airport of intended landing; it is not an instrument approach procedure. A visual approach may be requested by the pilot or offered by ATC. Visual approaches are possible when weather conditions permit continuous visual contact with the destination airport. They are issued in such weather conditions in order to expedite handling of IFR traffic. The ceiling must be reported or expected to be at least 1000 feet AGL (above ground level) and the visibility is at least 3 SM (statute miles).:4-57