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## Traffic Scanning

• Theopheonix 101
• Topic Author

### Theopheonix 101 created the topic: Traffic Scanning

The size of an aircraft on a collision course will,

A. appear stationary on the horizon
B. appear stationary and increase linearly
C. increase linearly
D. increase exponentially.

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 702

### John.Heddles replied the topic: Traffic Scanning

(a) appear stationary on the horizon

Collision trajectory implies nil relative motion. However, appearing on the horizon is a sufficient but not a necessary prerequisite for collision. So, no.

(b) appear stationary and increase linearly

Collision trajectory implies nil relative motion. However, as the range decreases, the visual angle of the target must increase with the increase becoming very non-linear at relative close ranges. So, no.

(c) increase linearly

As the range decreases, the visual angle of the target must increase with the increase becoming very non-linear at relative close ranges. So, no.

(d) increase exponentially.

Very much so as the aircraft range gets within the final few seconds prior to impact.

For instance, see fig 5.10 p 142. The graphic plots various speeds against visual angle change but, in effect, is talking about distance against visual angle.