{{short description, Type of radar instrument approach In

aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...

, approach surveillance radar (ASR or SRA) is a type of radar instrument approach provided with active assistance from

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airs ...

. The only airborne radio equipment required for radar approaches is a functioning radio transmitter and receiver. The radar controller vectors the aircraft to align it with the

runway According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt concrete, as ...

centerline. The controller continues the vectors to keep the aircraft on course until the pilot can complete the

approach Approach may refer to: Aviation *Visual approach *Instrument approach *Final approach Music * ''Approach'' (album), by Von Hertzen Brothers * ''The Approach'', an album by I:Scintilla Other uses *Approach Beach, a gazetted beach in Ting Kau, Ho ...

and landing by visual reference to the surface. There are two types of radar approaches: Precision (PAR) and Surveillance (ASR). A radar approach may be given to any aircraft upon request and may be offered to pilots of aircraft in distress or to expedite traffic; however, an ASR might not be approved unless there is an ATC operational requirement, or in an unusual situation or emergency. Acceptance of a PAR or ASR by a pilot does not waive the prescribed weather minimums for the airport or for the particular aircraft operator concerned. The decision to make a radar approach when the reported weather is below the established minimums rests with the pilot. PAR and ASR minimums are published on separate pages in the

FAA The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...

's terminal procedures publication.

Precision approach (PAR)

This is one in which a controller provides highly accurate navigational guidance in

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

and elevation to a pilot. Pilots are given headings to fly, to direct them to, and keep their aircraft aligned with the extended centerline of the landing runway. They are told to anticipate

glidepath Instrument landing system glide path, commonly referred to as a glide path (G/P) or glide slope (G/S), is "a system of vertical guidance embodied in the instrument landing system which indicates the vertical deviation of the aircraft from its o ...

interception approximately 10–30 seconds before it occurs and when to start descent. The published

decision height In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach to a landi ...

will be given only if the pilot requests it. If the aircraft is observed to deviate above or below the glidepath, the pilot is given the relative amount of deviation by use of terms “slightly” or “well” and is expected to adjust the aircraft rate of descent/ascent to return to the glidepath. Trend information is also issued with respect to the elevation of the aircraft and may be modified by the terms “rapidly” and “slowly” (e.g., “well above glidepath, coming down rapidly”). Range from touchdown is given at least once each mile. If an aircraft is observed by the controller to proceed outside of specified safety zone limits in azimuth and/or elevation and continue to operate outside these prescribed limits, the pilot will be directed to execute a

missed approach Missed approach is a procedure followed by a pilot when an instrument approach cannot be completed to a full-stop landing. The instructions for the missed approach may be assigned by air traffic control (ATC) prior to the clearance for the approac ...

or to fly a specified course unless the pilot has the runway environment (runway, approach lights, etc.) in sight. Navigational guidance in azimuth and elevation is provided to the pilot until the aircraft reaches the published decision height. Advisory course and glidepath information is furnished by the controller until the aircraft passes over the landing threshold, at which point the pilot is advised of any deviation from the runway centerline. Radar service is automatically terminated upon completion of the approach.

Surveillance approach

This is one in which a controller, in ASR, 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

surveillance Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing or directing. This can include observation from a distance by means of electronic equipment, such as c ...

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. Guidance in elevation is not possible but the pilot will be advised when to commence descent to the

minimum descent altitude In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach to a landi ...

(MDA) or, if appropriate, to an intermediate stepdown fix Minimum Crossing Altitude (MCA) and subsequently to the prescribed MDA. In addition, the pilot will be advised of the location of the MAPt prescribed for the procedure and the aircraft position each mile on final from the runway, airport, heliport, or MAPt, as appropriate. 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 that is at or above the MDA. Normally, navigational guidance will be provided until the aircraft reaches the MAPt. Controllers will terminate guidance and instruct the pilot to execute a missed approach unless at the MAPt the pilot has the runway, airport, or heliport in sight or, for a helicopter point-in-space approach, the prescribed visual reference with the surface is established. Also, if, at any time during the approach the controller considers that safe guidance for the remainder of the approach cannot be provided, the controller will terminate guidance and instruct the pilot to execute a missed approach. Similarly, guidance termination and missed approach will be effected upon pilot request and, for civil aircraft only, controllers may terminate guidance when the pilot reports the runway, airport, heliport or visual surface route (point-in-space approach) in sight or otherwise indicates continued guidance is not required. Radar service is automatically terminated at the completion of a radar approach. Pilots should check radar services at the airport they desire to land in order to determine if radar approaches are available. Radar approaches are used a lot by many navy/marine corps pilots as a default to emergencies, thus many navy/marine pilots are proficient in Radar approaches. Air traffic control Types of final approach (aviation)