Air traffic has become a significant concern for the aviation industry as skies are becoming crowded like roads or highways, increasing the chances of air collisions. Despite having advanced technologies present in the aerospace industry, such as ground-based radars, visual vigilance, and traffic control, maintaining air traffic has become an enormous challenge. Due to this situation, collision avoidance equipment has become increasingly normal in every aircraft to reduce the chance of mid-air collisions.
The aircraft collision avoidance system (ACAS) is equipment that works with the help of transponder signals from the secondary surveillance radar (SSR) to detect nearby aircraft while delivering alert signals to the pilot. Though the ACAS can reduce air traffic, it will not detect the aircraft without transponder equipment and cannot track nearby traffic during flight. Therefore, ACAS technology is also known as the traffic collision avoidance system (TCAS).
Monitoring air traffic and alerting systems can be separated into two categories: TCAS I and TCAS II types. The function of the TCAS I is to deal with regional airlines and the general aviation community while having the ability to identify traffic within a range of 35-40 miles of the aircraft to assist the pilot. The TCAS I is required on a plane with 30-35 seats, while the TCAS II is mandatory on aircraft with more than 30 seats. The TCAS II is more complex than its counterpart, and it serves to direct international flights and tracks the information of TCAS I equipped aircraft with projected flight paths. In addition, the TCAS II system will issue a resolution advisory when a collision occurs during flight and alerts the pilot in advance about hazardous situations.
Transponders of TCAS-equipped aircraft can track nearby transponders in other aircraft with the help of SSR technology. For detection, a 1090 MHz signal is sent before a reply is received from the examined transponder. A reply in the form of a1030 MHz signal is displayed on the TCAS computer screen with the altitude and position of the aircraft included. The position of the aircraft should be presented in terms of vertical and horizontal distances. Once a detection is made, a pilot must decide to take action according to the situation. TCAS II equipped aircraft observe the speed and position of nearby aircraft by continuously responding to detected information. Different colors and shapes categorize imminent threat levels to illustrate approaching aircraft on the flight deck screen, allowing pilots to optimally avoid any hazard.
Various displays are used in aircraft to display flight information, including versions of the electronic HSI or a multifunctional display that can portray both TCAS information and weather radar information. Due to resolution advisories (RAs) being limited to vertical evasive maneuvers, some aircraft use electronic vertical speed indicators to display TCAS information.
Several types of RAs are available for the pilot to comply with, but they can be broadly classified into two groups. Upward movement advisories can be classified as a climb, crossing climb, maintain climb, reversal climb, increase climb, preventive RA, etc. Meanwhile, downward advisories can be categorized as crossing descends, reversal descends, etc. Each RA has a set vertical limit to the pilot's response by taking the aircraft up or down. Generally, pilots must follow TCAS RAs over ATC commands when flying in a controlled airspace.
The sky is not as big and endless as it used to be with the great increase of air traffic. With many airplanes and helicopters available to private sectors and the public alike, more people are now flying, and it is getting harder for ATC to keep track of everything, especially in metropolitan areas. The ACAS system will help pilots avoid potential collisions by sending alerts if their computer detects an unsafe situation before air traffic control has a chance to assist. If you want to bolster the safety of your aircraft, you should always ensure that you have functional and reliable ACAS equipment.
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