Precision approach radar

Precision approach radar. It is a specialized type of radar system designed to guide aircraft to a safe landing, particularly under conditions of low visibility such as fog, rain, or darkness. Operated by controllers on the ground, it provides highly accurate real-time information on an aircraft's position relative to the ideal glide path and runway centerline. This technology was a critical component of aviation safety for decades, enabling all-weather operations at both military and civilian airports around the world before the widespread adoption of more automated systems.

Overview

The primary function is to support a ground-controlled approach, where a radar controller in a van or tower verbally instructs the pilot to correct their descent and alignment. This method was famously employed by the United States Army Air Forces during World War II and later by the United States Air Force, Royal Air Force, and Soviet Air Forces. Systems like the AN/MPN-14K became iconic, providing a vital safety net during the Berlin Airlift and the Korean War. Its use extended to major civilian airports, including London Heathrow Airport and John F. Kennedy International Airport, ensuring continuity of operations during Instrument meteorological conditions.

Technical description

A typical system consists of two high-resolution radar beams scanning independently. One beam, the azimuth scanner, rotates horizontally to track the aircraft's lateral deviation from the runway centerline, while the elevation scanner rotates vertically to monitor adherence to the ideal glide path, usually a 3-degree angle. These X band radars offer superior resolution and are less affected by weather than longer wavelengths. The raw radar returns are processed and displayed for the controller on specialized PPI scopes, often showing "crosshair" markers representing the ideal flight path. Key manufacturers included General Electric, Westinghouse Electric Corporation, and ITT Corporation, with later digital upgrades provided by companies like Northrop Grumman.

Operational use

During an approach, the aircraft is first detected by a companion airport surveillance radar like the AN/GPN-20, which hands off to the precision radar at about 10 nautical miles from the runway. The controller then issues continuous verbal instructions via radio, such as "on glide path, on centerline" or corrective commands like "come right two degrees." This procedure, standardized by the International Civil Aviation Organization, was essential for military aviation in conflicts from the Vietnam War to the Gulf War. Renowned units like the 1st Combat Evaluation Group at Holloman Air Force Base were experts in its deployment. The technique required significant skill from both controller and pilot, forming a core part of training at facilities like the Federal Aviation Administration Academy.

Historical development

Early development was driven by the United States Navy and the Massachusetts Institute of Technology Radiation Laboratory in the early 1940s, leading to the first operational system, the AN/MPN-1, deployed in 1943. Its success during the Battle of the Bulge and the Pacific War proved its worth. The post-war era saw rapid advancement, with the AN/CPN-18 introducing improved stability. The Cold War accelerated its adoption by NATO and Warsaw Pact forces; the Soviet Union fielded systems like the RP-5. The 1960s and 1970s represented its peak, with installations worldwide. However, the development of fully automated ILS and later MLS and GPS-based Satellite navigation began to render the labor-intensive PAR procedure obsolete for routine use by the late 20th century.

Comparison with other landing systems

Unlike the Instrument Landing System, which provides guidance directly to the pilot's cockpit instruments via radio waves, it requires a human controller as an intermediary. While ILS became the international standard for Category I, II, and III landings due to its automation, PAR offered advantages in flexibility and rapid deployment, as seen with mobile units during the Falklands War. It was also less susceptible to multipath interference from terrain than early ILS installations. Compared to the modern Microwave Landing System or Ground-Based Augmentation System like the Local Area Augmentation System, it is a more resource-intensive, manually driven technology. Today, its role is largely supplanted by these systems, though it remains in limited use for military training and as a backup at some remote airfields. Category:Radar Category:Aviation safety Category:Aviation navigation systems