What should be observed during the fire detection tests?

During fire detection tests, it's critical to observe warning indicators and tones. This process is essential because it verifies that the fire detection system functions as intended, ensuring that any potential fire threats are promptly identified. If a fire were to occur, timely alerts can lead to quicker responses, potentially saving lives and equipment. The system is designed to activate visual and audio warnings in the cockpit and other crew areas, signaling the presence of fire or an abnormal temperature rise.

The other options do not pertain directly to the primary focus of fire detection tests. For example, APU start parameters and power output levels may be relevant for assessing performance and operational readiness, but they do not provide insights specific to fire detection systems. Likewise, while fuel efficiency metrics are important for overall aircraft operation, they are unrelated to the task of confirming that fire detection mechanisms are operational. Thus, monitoring warning indicators and tones is the appropriate action during these tests.