Collision avoidance system for aircraft

Abstract

A collision avoidance system for aircraft in which one aircraft is equipped with an interrogation station having a secondary surveillance radar. .[.Coarse.]. .Iadd.A .Iaddend.distance measurement is effected either by passive or active distance measurement or by both of them. If the detected distance lies within a certain limit, the output power and/or period of the interrogation signal of the secondary surveillance radar of the subject aircraft is altered .[.so as to effect fine distance measurement.].. This system can be applied without increasing interference against the existing secondary surveillance radar system by keeping the output power and period of interrogation signal in a minimum required extent. By the same reason the system can keep the interference at a small extent between proximate aircraft, each mounting this collision avoidance system.

What is claimed is: .[.1. A collision avoidance system for aircraft each equipped with an ATC transponder comprising; 
     
        from the ATC transponder of the second aircraft..]. .[.6.  The collision avoidance system for aircraft as claimed in claim 1, wherein said coarse detection means deduces the variation of altitude difference between the aircraft by consecutively deducing altitude difference information..]. .[.7. The collision avoidance system for aircraft as claimed in claim 1, wherein the output control means for altering at least one of output power and transmission period of the interrogation signal sent from the interrogation station functions in response to detected variation of time difference between transmission of the interrogation signal and reception of the response signal..]. .[.8. The collision avoidance system for aircraft as claimed in claim 1, wherein the output control means functions in response to detection of the repetition frequency of the response signals, i.e. number of responses during a certain duration, sent from the ATC transponder on the second aircraft..]. .[.9. The collision avoidance system for aircraft as claimed in claim 1, wherein said output control means functions in response to detection of repetition frequency of interrogation signals sent from ground secondary surveillance radar, i.e. number of second interrogation signals during a certain duration..]. .[.10. Collision avoidance system as claimed in claim 5, wherein the response signal of the other aircraft is sent in response to an interrogation signal sent from the interrogation station mounted on said one aircraft..]. .[.11. Collision avoidance system as claimed in claim 6, wherein the response signal of the other aircraft is sent in response to an interrogation signal sent from the interrogation station mounted on 
     
     
        said one aircraft..]. .Iadd.12.  A collision avoidance system for aircraft which are each equipped with an ATC transponder comprising: an interrogation station located on a first aircraft and having a secondary surveillance radar function, said interrogation station emitting an interrogation signal which is to be responded to by an ATC transponder of a second aircraft;   a detection means located on said first aircraft for detecting the existence of said second aircraft in proximity to said first aircraft;   an output control means operatively connected to said detection means for altering at least one of an output power and a transmission period of said interrogation signal emitted by said interrogation station when said detection means detects information concerning said second aircraft which exceeds a predetermined value. .Iaddend. .Iadd.13. A collision avoidance system as recited in claim 12, wherein said detection means deduces distance between said first and second aircraft by detecting a time difference between reception of a second interrogation signal by said first aircraft which has been sent from a ground secondary surveillance radar and a response signal sent from said ATC transponder located on said second aircraft, said response signal being generated in response to said second interrogation signal. .Iaddend. .Iadd.14. A collision avoidance system as recited in claim 12, wherein said detection means deduces distance between said first and second aircraft by detecting a time difference between transmission of said interrogation signal sent from said interrogation station located on said first aircraft and a response signal sent from said ATC transponder located on said second aircraft, said response signal being generated in response to said interrogation   
     
     
        signal. .Iaddend. .Iadd.15.  A collision avoidance system as recited in claim 12, wherein said detection means deduces distance between said first and second aircraft by detecting a received level of a response signal generated by said ATC transponder located on said second aircraft when said response signal is responding to an interrogation signal sent from a ground interrogation station. .Iaddend. .Iadd.16. A collision avoidance system as recited in claim 12, wherein said detection means deduces altitude difference information between said first and second aircraft by detecting altitude information included in a response signal generated by said ATC transponder of said second aircraft. .Iaddend. .Iadd.17. A collision avoidance system as recited in claim 12, wherein said detection means deduces variations of altitude difference between said first and second aircraft by consecutively deducing altitude difference information. .Iaddend. .Iadd.18. A collision avoidance system as recited in claim 12, wherein said output control means functions in response to a detected variation of time difference between transmission of said interrogation 
     
     
        signal and a reception of said response signal. .Iaddend. .Iadd.19.  A collision avoidance system as recited in claim 12, wherein said output control means functions in response to a detection of the number of response signals during a predetermined time period generated by said ATC transponder located on said second aircraft. .Iaddend. .Iadd.20. A collision avoidance system as recited in claim 12, wherein said output control means functions in response to a detection of the number of interrogation signals during a predetermined time period generated by a 
     
     
        ground secondary surveillance radar. .Iaddend. .Iadd.21.  A collision avoidance system as recited in claim 16, wherein said response signal of said second aircraft is generated in response to said interrogation signal generated by said interrogation station located on said first aircraft. .Iaddend. .Iadd.22. A collision avoidance system as recited in claim 17, wherein said response signal of said second aircraft is generated in response to said interrogation signal generated by said interrogation station located on said first aircraft. .Iaddend.