Which of the following actions is crucial before launching a flyer?

The action of double-checking the harness and carabiner lock is crucial before launching a flyer because safety is paramount in any activity that involves heights or potential fall risks. The harness and carabiner are the primary means of securing the flyer, ensuring they are safely attached to the ride system. A secure harness prevents any possibility of a fall, which could lead to serious injury. This step is a direct measure of protecting the flyer’s safety during the experience.

While confirming that conditions are optimal, ensuring bystanders are clear, and testing the full system operation are all important safety measures, they serve more as additional layers of precaution rather than the immediate physical safety check that comes from ensuring the harness and carabiner are locked and secure. Thus, double-checking this equipment is a non-negotiable step that must precede any launch.