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intervals depending on the type of approach flow and phase of the approach. In order to land, pilots must have the runway or runway environment in sight prior to reaching the "decision height," for PAR approaches (usually 100–400 ft above the runway touchdown zone) or prior to the "Missed
Approach Point" for non-precision approaches. The published minimum visibility and decision height/minimum descent altitude vary depending upon the approach and runway lighting, obstacles in the approach corridor, type of aircraft, and other factors. Pilots of revenue flights periodically must demonstrate PAR approach proficiency, and GCA controllers must conduct a minimum number of such approaches in a year to maintain competency.
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communication radio works. Sometimes the PAR-based ground-controlled approach is also requested by qualified pilots when they are dealing with an emergency on board to lighten their workload. In the United States, instrument approaches must be monitored by a PAR (if one exists with a coinciding final approach course) during certain condition such as times of darkness or low weather depending upon the controlling agency (USAF, U.S. Army, USN or FAA) or upon pilot request.
62:(ASR, providing a non-precision surveillance radar approach with no glidepath guidance). The term GCA may refer to any type of ground radar guided approach such as a PAR, PAR without glideslope or ASR. When both vertical and horizontal guidance from the PAR is given, the approach is termed a precision approach. If no PAR glidepath is given, even if PAR equipment is used for lateral guidance, it is considered a non-precision approach.
239:, provided horizontal guidance only, and was not accurate enough to use for a primary landing system. ILS offered the required accuracy and vertical guidance, but would require new radios and instruments to be added to every aircraft. As GCA also required only a normal radio receiver to operation, it would be much easier to use with the vast bomber fleets.
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By following controller commands to keep the landing aircraft on both glidepath and approach centerline, a pilot will arrive precisely over the runway's touchdown zone. In order to insure continuous radio communication integrity, controllers are required to make radio transmissions at certain minimum
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concept, which greatly increases the angular accuracy of the radar by rotating the beam around a cone-shaped pattern about 15 degrees across. This caused the beam to periodically sweep across the water when it was pointed near the horizon, which would often be the case as the aircraft approached the
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from the controller, and can serve many aircraft at the same time. The ground-controlled approach is useful when the approaching aircraft is not equipped with sophisticated navigation aids, and may also become a life saver when an aircraft's on-board navigation aids are inoperative, as long as one
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pilot and was aware of the problems landing aircraft in bad weather. He quickly asked whether the XT-1 could be used for this role; once locked-on to a single aircraft, the radar operator could read the radar displays and give instructions to the pilot to talk them down to a point close to the
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Because of their labor-intensive nature—one GCA controller is normally required for each aircraft on final approach—GCAs are no longer in widespread use at civilian airports, and are being discontinued at many military bases. However, air traffic controllers at some locations in the
365:(ILS). Global Positioning System (GPS) based approaches that provide both lateral and vertical guidance are coming into widespread use, with approach minima as good as, or nearly as good as, GCA or ILS. Modern ILS and GPS approaches eliminate the possibility of
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of approaching aircraft. The controllers then provide verbal instructions by radio to the pilots to guide them to a landing. The instructions include both descent rate (glidepath) and heading (course) corrections necessary to follow the correct approach path.
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Ground-controlled approach is the oldest air traffic technique to fully implement radar to service a plane. The system was simple, direct, and worked well, even with previously untrained pilots. It requires close communication between ground-based
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are required to maintain currency in their use, while the
Belgian Air Force still uses the PAR for ground-controlled approaches on a daily basis. NATO has kept GCA active while civil aviation adopted the
165:"squeeze box" that performed the same scanning without the antennas moving. Mark II also introduced the "expanded-partial-plan-position-indicators", later replaced with the simpler name "beta scan".
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runway. On 10 November 1941, he was granted time on the XT-1 and successfully measured the position of a landing aircraft with the required accuracy. In the spring of 1942, XT-1 was moved to
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The UK kept in close contact with their RadLab counterparts, and immediately expressed an interest in the system. The UK had developed their own low-precision approach system based on the
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was carried out on 14 February 1943. This resulted in an immediate contract from the Army Signal Corps for 57 examples of what they called the MPN-1A from
Gilfillan while the
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The first example of the new system, known as Mark I, began testing in
November 1942. A further improved version, Mark II, replaced the mechanical scanning antennas with a
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had nearly run out of fuel and was forced to land in spite of bad weather. The Mark I operator talked the PBY down into a successful landing, the first "save".
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and pilots in approaching aircraft. Only one pilot is guided at a time (max. 2 under certain circumstances). The controllers monitor dedicated
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The first examples of the production AN/MPN-1A were delivered to the Army in the fall of 1944. The first operational unit was placed in
80:
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placed a second contract for 80 MPN-IC from Bendix Radio. Several additional orders followed, including an Army order for 200 from
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estuary. Here the system demonstrated itself incapable of distinguishing between the aircraft and its reflection off the water.
158:(PAR), with separate antennas for vertical and horizontal guidance that were moved in such a way to avoid seeing the ground.
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airfield. This order helped cement US interest in the system, and they agreed to leave the prototype in the UK.
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where
Alvarez began shooting approaches using the system. Navy Ensign Bruce Giffin soaped the windshield of his
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for testing. Over the next months, over 270 approaches were carried out, including the return of 21
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181:(ILS) for this role, and they displayed no interest in the new system. However, in June 1942 the
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whereby they guide aircraft to a safe landing, including in adverse weather conditions, based on
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557:, July 1946, pp. 82–84, first detailed article for general public on GCA radar.
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150:(ASR) that brought the aircraft into the general area of the airport, and a second
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known as XT-1, which had the ability to automatically track a selected target once
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Azimuth, showing the aircraft's position relative to the horizontal approach path.
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Meanwhile, testing with the Mark I continued. In
November 1942 it was moved to
511:"Invention of Ground Control Approach Radar at the MIT Radiation Laboratories"
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concept, which relied only on a normal audio radio receiver. This system, the
107:. Production versions of the XT-1 would begin deliveries in 1944 as the famed
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Clarke contributed to the early application of GCA. GCA was developed during
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Ground-controlled approaches have been depicted in several films, including
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was poor. It was essential for maintaining the flow of supplies during the
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Elevation, showing vertical position relative to the published glidepath.
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Two tracks are displayed on the
Precision Approach Radar (PAR) scope:
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in
December. Units were soon delivered to the Pacific, installed at
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on an operational mission on the night of 23 August. This led to a
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87:. The "RadLab" had formed to develop radar systems based on the
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The GCA concept was originally developed by nuclear physicist
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to demonstrate his trust in the system. On 1 January 1943, a
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images. Most commonly, a GCA uses information from either a
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In June 1943, Mark I was sent to the UK aboard battleship
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A new methodology was developed in May 1942, combining an
83:, in 1941 Alvarez was invited to join the recently opened
469:"JO 7110.65Y - Air Traffic Control Document Information"
99:, the RadLab had already developed a prototype of a new
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to enable pilots returning to base to land safely when
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In early 1946, three surplus MPN- 1 were given to the
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ordered ten examples anyway, giving the contract to
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Type of service provided by air-traffic controllers
91:, revealed to them by its UK inventors during the
405:fictionalizes the original development of GCA.
123:, where the landing path extended out over the
317:systems, to determine the precise course and
183:Office of Scientific Research and Development
95:in late 1940. By the time Alvarez arrived in
54:(PAR, for precision approaches with vertical
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336:makes a ground-controlled approach, 1964.
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177:had already widely deployed the SCS-51
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207:This story caught the attention of
173:By the time Mark II was ready, the
42:) is a type of service provided by
571:Types of final approach (aviation)
261:request for a GCA radar for every
81:University of California, Berkeley
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473:Federal Aviation Administration
121:Elizabeth City, North Carolina
1:
437:– Transponder Landing System
237:Blind Approach Beacon System
430:Beam Approach Beacon System
290:Washington-National Airport
269:Deliveries and post-war use
213:Washington National Airport
18:Surveillance radar approach
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446:Index of aviation articles
148:airport surveillance radar
60:airport surveillance radar
36:ground-controlled approach
552:"Radar Becomes Lifeline."
515:IEEE AES Systems Magazine
509:Jolley, Neal (May 1993).
363:instrument landing system
211:, and a demonstration at
202:Consolidated PBY Catalina
179:instrument landing system
315:precision approach radar
156:precision approach radar
85:MIT Radiation Laboratory
52:precision approach radar
311:air traffic controllers
286:Civil Aeronautics Board
44:air-traffic controllers
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135:XT-1 was based on the
375:Strategic Air Command
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79:. Originally of the
114:Alvarez was also a
101:anti-aircraft radar
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263:RAF Bomber Command
187:Gilfillan Brothers
175:US Army Air Forces
527:10.1109/62.212592
294:LaGuardia Airport
71:Early experiments
16:(Redirected from
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397:Arthur C. Clarke
251:RAF Elsham Wolds
249:and emplaced at
189:in Los Angeles.
137:conical scanning
125:Pasquotank River
89:cavity magnetron
58:guidance) or an
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555:Popular Science
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77:Luis Alvarez
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367:human error
233:Lorenz beam
227:UK interest
154:radar, the
105:"locked-on"
452:References
414:visibility
402:Glide Path
259:Lend-Lease
521:(5): 57.
399:'s novel
391:Skyjacked
331:U.S. Navy
163:waveguide
56:glidepath
565:Category
535:33655059
424:See also
334:Sea King
319:altitude
304:Overview
279:Iwo Jima
140:ground.
32:aviation
383:Airport
217:US Navy
109:SCR-584
66:History
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441:AN/MPN
389:, and
296:, and
275:Verdun
152:X-band
145:S-band
97:Boston
531:S2CID
387:Julie
244:HMS
34:, a
523:doi
435:TLS
221:ITT
198:SNB
40:GCA
30:In
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