What are the limitations of primary surveillance radar in air traffic control?

Primary surveillance radar (PSR) has several limitations in air traffic control, stemming from its reliance on reflected radio waves to detect aircraft, providing only limited information and susceptibility to various interference factors. PSR works by emitting a radio signal and detecting the signal that bounces back off an object. One major limitation is its inability to determine an aircraft's altitude directly. While PSR can provide horizontal position (azimuth and range), altitude information relies on secondary surveillance radar (SSR) or pilot reports. Another limitation is its susceptibility to clutter and interference. Reflections from terrain, weather, and other objects can create false targets on the radar screen, making it difficult to distinguish between aircraft and non-aircraft targets. This clutter can reduce the accuracy and reliability of the radar data. PSR also has limited range and coverage. The range of a PSR system is limited by the power of the transmitter, the sensitivity of the receiver, and the curvature of the Earth. Additionally, PSR coverage can be blocked by terrain or buildings, creating blind spots in the radar's coverage area. PSR does not provide aircraft identification information. Without secondary surveillance radar, controllers cannot readily identify specific aircraft based solely on the primary radar return. The radar display only shows a blip, which could represent any aircraft or even a weather phenomenon. Weather can significantly degrade PSR performance. Heavy precipitation can attenuate the radar signal, reducing its range and accuracy. Furthermore, weather can create significant clutter on the radar screen, making it difficult to detect aircraft. Finally, PSR only provides information about aircraft that are within its coverage area. Aircraft operating outside of the radar's coverage area are not visible to the controller. Therefore, these limitations necessitate the use of secondary surveillance radar and other technologies to provide a more complete and reliable picture of air traffic.