What is a Precision Approach Radar?

A Precision Approach Radar (PAR) system is a ground-based radar that is used to guide an aircraft during landing, especially in low-visibility conditions. It is a crucial tool in modern aviation that provides the precision needed for safe landing as it provides horizontal and vertical guidance to pilots. It consists of radar antennas that transmit and receive echoes to determine the vertical and horizontal positions of the aircraft, a display system and a real-time communication system. 

Precision approach radars are most frequently used at military air traffic control facilities. Most of the facilities use the AN/FPN-63, AN/MPN, or AN/TPN-22. These radars can provide precision guidance from a distance of 10 to 20 miles down to the runway threshold. PAR is mostly used by the Navy, as it does not broadcast directional signals which might be used by an enemy to locate an aircraft carrier. 

AN/TPN-12 GCA/PAR 

The PAR radars use a unique type of radar display with two separate “traces” separated vertically. The upper trace shows the elevation of a selected aircraft compared to a line displaying the ideal glideslope, while the lower shows the aircraft’s horizontal position relative to the runway midline.  

Working of a Precision Approach Radar

The PAR is placed near the mid-point of the runway (at a distance of up to 6 ft) and works remotely. It has two antennas that emit high-frequency radar signals which spread out in a specific pattern covering the runway. As these signals encounter an aircraft, they are reflected back towards the radar antenna. The reflected signals are captured by the sensitive receivers of the radar antenna and provide lateral and vertical guidance. The horizontal antenna moves 20 degrees from the runway centerline to provide azimuth (lateral guidance) and distance information. The vertical antenna moves from -1 to 15 degrees up and down to provide the height and target distance.  

The controllers monitoring the PAR display observe each aircraft’s position and issue instructions to the pilot to keep the aircraft on course and on the glide path during the final approach. After the aircraft reaches the decision height, further guidance is optional. 

Advantages of a Precision Approach Radar

The Precision Approach Radar system provides highly accurate real-time guidance to pilots during the critical phases of landing, thereby providing enhanced safety by reducing the risks of landing-related accidents. Due to this technology, aircraft can land safely in adverse weather conditions such as fog, rain, etc., where the visibility becomes low. The controllers present in the PAR system can communicate directly with the pilot in real-time, which helps with immediate feedback and allows the pilot to make timely adjustments. Also, no specific equipment is required in the aircraft as PAR is a ground controller approach where controllers from the ground provide lateral and vertical guidance. 

Disadvantages of a Precision Approach Radar

Although the Precision Approach Radar (PAR) is highly effective for guiding aircraft during landing, it has certain disadvantages which impact its practicality and efficiency in modern aviation operations. The PAR system requires specialized radar equipment that is expensive to install and maintain. Also, dedicated controllers are required to be assigned to each flight to provide navigation, which increases the workload for the controllers.

For these reasons and with advancements in onboard navigation systems & wider ILS availability, PAR usage is less common in civil aviation compared to the past.