Passage Summary: The author argues that a specific radar system makes flying safer because it helps avoid collisions, despite the fact that it sometimes gives false alarms.

Conclusion: Passengers are safer on airplanes equipped with collision-avoidance radar than on those without it.

Reasoning: The system provides pilots with proximity information and prompts evasive action during potential collisions, even though it occasionally triggers for non-existent 'phantom' planes.

Analysis: This 'Necessary Assumption' question requires us to find a hidden requirement for the conclusion to hold true. The author admits the system has a flaw—false alarms—but still insists it is safer overall. Therefore, the argument must assume that the 'evasive action' taken to avoid these phantom planes does not create a danger that outweighs the safety benefits of the system. If dodging a ghost plane was more dangerous than a potential collision, the conclusion would fall apart.