{"id":14506,"date":"2025-06-07T16:25:11","date_gmt":"2025-06-07T10:55:11","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14506"},"modified":"2025-06-10T12:47:15","modified_gmt":"2025-06-10T07:17:15","slug":"aircraft-collision-warning-system","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/aircraft-collision-warning-system\/","title":{"rendered":"Airborne Collision Avoidance System (ACAS)"},"content":{"rendered":"\n<h2>Airborne Collision Avoidance System<\/h2>\n\n\n\n<h3>Introduction to ACAS<\/h3>\n\n\n\n<ul><li>Airborne collision avoidance system is called Traffic collision avoidance system<\/li><li>TCAS II is mandatory for all commercial aircraft with 19 passengers or more<\/li><li>TCAS II detects, assesses and warns of collision risk<\/li><li>Warnings consist of Traffic and Resolution Advisories<\/li><li>Traffic Advisories provide proximity traffic information only.<\/li><li>Resolution Advisories offer maneuvering advice in the vertical plane.<\/li><\/ul>\n\n\n\n<h3>Principle of ACAS<\/h3>\n\n\n\n<ul><li>ACAS works on the principle of secondary radar in air to air mode<\/li><li>Minimum requirement for ACAS are Mode A SSR transponders<\/li><li>Frequencies used is 1030 to 1090 MHz just like SSR<\/li><li>TCAS creates two protective three-dimensional bubbles around aircraft<\/li><li>Bubbles represent the time to closest point of contact<\/li><\/ul>\n\n\n\n<h3>Types of ACAS Advisories<\/h3>\n\n\n\n<ul><li>ACAS provides advisories based on the type of transponder<ul><li>Mode A does not transmit height therefore can only give Traffic Advisories.<\/li><li>Mode C transponders provide both traffic as well as resolution advisories<\/li><li>Mode S transponders allow mutually resolved avoidance maneuvers<\/li><\/ul><\/li><\/ul>\n\n\n\n<h3>Operation of ACAS-TCAS<\/h3>\n\n\n\n<ul><li>TCAS measures range of an intruder by measuring the time lapse principle.<\/li><li>Interrogation signal is sent once a second and detection range of 30 NM.<\/li><li>Reduced surveillance mode is used in high traffic density areas<\/li><li>Interrogation signal is sent once in 5 seconds and detection range is 5 NM.<\/li><li>Altitude information is obtained directly from the Mode C transponder<\/li><li>Bearing of an intruder is determined by a directional antenna.<\/li><li>Resolution of bearings by ACAS is un reliable due to short wavelength<\/li><li>Collision avoidance commands are not given in the horizontal plane<\/li><\/ul>\n\n\n\n<h3>Traffic Advisory<\/h3>\n\n\n\n<ul><li>Traffic Advisories cautions when an intruder penetrates the outer bubble<ul><li>TA means that the traffic is between 45 and 35 seconds to collision<\/li><li>TAs appear as solid yellow amber circles on the TCAS display<\/li><li>Synthetic voice announces \u00e2\u20ac\u0153Traffic, Traffic\u00e2\u20ac\u009d<\/li><\/ul><\/li><\/ul>\n\n\n\n<h3>Preventive Resolution Advisory<\/h3>\n\n\n\n<ul><li>Resolution Advisories alerts if intruder penetrates the inner bubble<\/li><li>RA means traffic is between 35 and 15 seconds from the collision<\/li><li>RAs appear as solid red rectangles on the TCAS<\/li><li>Synthetic voice warnings are issued.<\/li><li>Preventative Advisories indicates no collision risk unless levels change<\/li><li>The synthetic voice advisory is \u00e2\u20ac\u0153Monitor Vertical Speed\u00e2\u20ac\u009d<\/li><\/ul>\n\n\n\n<h3>Corrective Resolution Advisory<\/h3>\n\n\n\n<ul><li>Corrective Resolution Advisories are situations where collision risk exists<\/li><li>Manoeuvre is necessary to avert collision.<\/li><li>The synthetic voice produces the appropriate command<ul><li>Reduce Climb<\/li><li>Increase Climb<\/li><li>Descend<\/li><li>Reduce Descent<\/li><\/ul><\/li><\/ul>\n\n\n\n<h3>Mode S SSR Advisory<\/h3>\n\n\n\n<ul><li>Mode S transponder uses unique identification<\/li><li>Resolution advisories with Mode S are coordinated between aircrafts<\/li><li>One of the traffic is asked to climb and the other advised to descend<\/li><\/ul>\n\n\n\n<h3>Proximate Traffic<\/h3>\n\n\n\n<ul><li>Proximate Traffic appears as a solid cyan diamond<\/li><li>Aircraft within 6 NM and within 1200 feet relative height.<\/li><li>Other Traffic appears as hollow cyan diamond<\/li><li>Aircraft within range of the display and within 2700 feet relative height<\/li><li>Climb or Descend switch is selected for climb and descend respectively<ul><li>During climb scan is 8700 feet above and 2700 feet below<\/li><li>During descent scan is 2700 feet above and 8700 feet below<\/li><\/ul><\/li><li>A + sign indicates the intruder is above, &#8211; sign below.<\/li><li>A trend arrow \u00e2\u2020\u2018 or \u00e2\u2020\u201c appears if intruder\u00e2\u20ac\u2122s vertical rate is 500 feet per minute<\/li><\/ul>\n\n\n\n<h3>ACAS Display<\/h3>\n\n\n\n<ul><li>TCAS information is displayed on one of the three displays<ul><li>Electronic Flight Information System<\/li><li>Weather radar<\/li><li>Independent display<\/li><\/ul><\/li><\/ul>\n\n\n\n<h3>Restricted Advisories<\/h3>\n\n\n\n<ul><li>TCAS and Radio altimeter modifies RAs in proximity to the ground.<ul><li>No instructions given when the aircraft is below 400 ft AGL<\/li><li>No descent RAs are given below 1000 ft AGL<\/li><li>No increase rate of descent commands below 1450 ft AGL.<\/li><\/ul><\/li><li>TCAS and Aircraft configuration modifies certain RAs<\/li><li>Climb RAs are avoided with gear and flaps down<\/li><li>TCAS and ADC modifies certain RAs<\/li><li>Climb RA are avoided close to its performance ceiling<\/li><\/ul>\n\n\n\n<h3>Action on ACAS Advisories<\/h3>\n\n\n\n<ul><li>Action on Traffic Advisories<ul><li>Start visual search and identify the intruder.<\/li><li>Contact ATC if the intruder is not located.<\/li><\/ul><\/li><li>Action on Resolution Advisories<ul><li>Initiate required manoeuvres as advised<\/li><li>Look out for other aircraft and inform ATC<\/li><\/ul><\/li><li>Resolution Advisories can be ignored only if conflicting traffic is visually located<\/li><li>If ATC and ACAS provide conflicting advise, ACAS advisory must be followed<\/li><\/ul>\n\n\n\n<h2>Share this Page<\/h2>\n","protected":false},"excerpt":{"rendered":"<p>Airborne Collision Avoidance System Introduction to ACAS Airborne collision avoidance system is called Traffic collision avoidance system TCAS II is mandatory for all commercial aircraft with 19 passengers or more TCAS II detects, assesses and warns of collision risk Warnings consist of Traffic and Resolution Advisories Traffic Advisories provide proximity traffic information only. Resolution Advisories offer maneuvering advice in the vertical plane. Principle of ACAS ACAS works on the principle of secondary radar in air to air mode Minimum requirement for ACAS are Mode A SSR transponders Frequencies used is&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false},"categories":[345],"tags":[],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14506"}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=14506"}],"version-history":[{"count":0,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14506\/revisions"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14506"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14506"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14506"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}