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The story behind the radar: How did Luis Alvarez lead the birth of GCA?
In aviation, a ground controlled approach (GCA) is a service provided by air traffic controllers who guide aircraft to safe landing, including in adverse weather conditions, based on primary radar imagery. The information most commonly used by GCA comes from Precision Approach Radar (PAR) or Airport Surveillance Radar (ASR). However, the birth of this technology is inseparable from the wisdom of a nuclear physicist, Luis Alvarez.
Early Experiments
The concept of GCA was first proposed by Luis Alvarez, a nuclear physicist at the University of California, Berkeley. In 1941, he was invited to join the newly opened MIT Radiation Laboratory, which was aimed at developing radar systems based on cavity magnetrons. When Alvarez arrived in Boston, the lab had already developed a new anti-air gun radar prototype, the XT-1.
"Alvarez quickly realized the difficulty of landing an aircraft in bad weather and proposed that the XT-1 could be used for such purposes."
In November 1941, Alvarez achieved his first success with the XT-1, accurately measuring the position of a landing aircraft. In the spring of 1942, the XT-1 was moved to Elizabeth City, North Carolina, where the landing path extended to the Pasquotank River, where the system was unable to distinguish between the aircraft and its reflection on the water.
New Scanner
XT-1 is based on the concept of conical scanning, which improves the angular accuracy of the radar. With the advent of new methods, including S-band Airport Surveillance Radar (ASR) and X-band Precision Approach Radar (PAR), aircraft are able to safely enter the vicinity of airports. The new system, called the Mark I, began testing in November 1942.
“The Mark II introduced the waveguide ‘squeeze box’ which further improved scanning efficiency.”
First Order
Although the US Army Air Forces, which already had extensive use of the SCS-51 Instrument Landing System (ILS) at the time, had little interest in a new system, in June 1942 the Office of Scientific Research and Development placed an order for ten Mark I radar. The technology was successfully used to rescue a PBY Catalina that was about to run out of fuel in January 1943, sparking the Pentagon's interest in the system.British Interest
During World War II, Britain maintained close ties with RadLab and showed great interest in the system. In June 1943, the Mark I was sent to the United Kingdom for testing, where it successfully performed over 270 approaches, demonstrating its effectiveness in bad weather, which triggered a requirement for the GCA radar from the RAF.
Delivery and post-war use
The first production AN/MPN-1A was delivered to the U.S. Army in 1944 and soon entered service in the Pacific. Over time, the GCA system was implemented at most airports in Europe and the Pacific. In 1946, three surplus MPN-1s were handed over to the United States Civil Aeronautics Administration, marking the GCA's long service in civil aviation.
SummaryGround controlled approach technology was one of the first air traffic technologies to fully implement radar. Not only is the system simple and straightforward, it is also effective even for pilots who have not received professional training. Although the modern aviation industry has turned to the use of more advanced instrument landing systems (ILS) and global positioning systems (GPS), GCA is still an important means to ensure safe landing when faced with aircraft without advanced navigation assistance systems.
This technology has been shown in several movies, but how many people remember its true story?
