A system for warning a pilot of a risk of collision, the system comprising: a first camera mounted at a first height to a leading edge of a vertical stabilizer of an aircraft for generating a first stream of video frames that include first image data representing an image of an object in a scene and second image data representing an image of a portion of the aircraft; a second camera mounted at a second height to the leading edge of the vertical stabilizer for generating a second stream of video frames that include third image data representing an image of the object in the scene and fourth image data representing an image of the portion of the aircraft, wherein the second height is less than the first height; a cue system on a flight deck of the aircraft capable of generating a cue; and a computer system programmed to: process the video frames of the first and second streams to determine a first range to the object and a first range rate at which the range to the object is changing at a first time, wherein the video frames of the first and second streams are processed using a stereoscopic technique to estimate a depth of the object, wherein the video frames of the first and second streams are processed using a structure from motion technique to estimate a three-dimensional structure of the scene, the range rate being determined based on a change in range across one or more frames together with a given frame rate of the first and second cameras, the known geometry of the aircraft and the installation position of the first and second cameras; compute a first time to collision based on at least the first range and first range rate; and trigger the cue system to produce a first cue in response to the first time to collision being less than a first detection threshold. a first camera mounted at a first height to a leading edge of a vertical stabilizer of an aircraft for generating a first stream of video frames that include first image data representing an image of an object in a scene and second image data representing an image of a portion of the aircraft; a second camera mounted at a second height to the leading edge of the vertical stabilizer for generating a second stream of video frames that include third image data representing an image of the object in the scene and fourth image data representing an image of the portion of the aircraft, wherein the second height is less than the first height; a cue system on a flight deck of the aircraft capable of generating a cue; and a computer system programmed to: process the video frames of the first and second streams to determine a first range to the object and a first range rate at which the range to the object is changing at a first time, wherein the video frames of the first and second streams are processed using a stereoscopic technique to estimate a depth of the object, wherein the video frames of the first and second streams are processed using a structure from motion technique to estimate a three-dimensional structure of the scene, the range rate being determined based on a change in range across one or more frames together with a given frame rate of the first and second cameras, the known geometry of the aircraft and the installation position of the first and second cameras; compute a first time to collision based on at least the first range and first range rate; and trigger the cue system to produce a first cue in response to the first time to collision being less than a first detection threshold. process the video frames of the first and second streams to determine a first range to the object and a first range rate at which the range to the object is changing at a first time, wherein the video frames of the first and second streams are processed using a stereoscopic technique to estimate a depth of the object, wherein the video frames of the first and second streams are processed using a structure from motion technique to estimate a three-dimensional structure of the scene, the range rate being determined based on a change in range across one or more frames together with a given frame rate of the first and second cameras, the known geometry of the aircraft and the installation position of the first and second cameras; compute a first time to collision based on at least the first range and first range rate; and trigger the cue system to produce a first cue in response to the first time to collision being less than a first detection threshold.