What is the reserve fuel supply requirement for a domestic air carrier flight?

The requirement for reserve fuel supply for a domestic air carrier flight is defined by regulations intended to ensure that aircraft have enough fuel to handle unforeseen circumstances. The correct option states that a flight must carry reserve fuel equating to 30 minutes of flight at normal fuel consumption, in addition to 15% of the fuel required to reach the alternate airport.

This requirement is vital because it accounts for potential delays in reaching the destination or alternate airport, including factors such as weather, air traffic control delays, or other unpredictable elements. The reserve fuel not only provides a safety margin for the flight but also ensures compliance with aviation regulations aimed at maintaining operational safety.

While other options might suggest alternative reserve requirements, they do not align with the specific regulations that govern domestic air carrier operations. For instance, carrying 45 minutes of fuel or even one hour as described in other choices does not adequately adhere to the structured guideline that incorporates both a time factor and a percentage-based contingency. Therefore, the option that specifies both the time and percentage of fuel required for the alternate airport provides a comprehensive approach that upholds safety protocols for domestic flights.