What is a limitation for on-demand flight time in a quarter?

The limitation for on-demand flight time in a quarter is indeed 500 hours. This standard is in accordance with regulations governing Part 135 operations which stipulate the maximum flight hours allowed for pilots in on-demand service within a quarterly period.

Understanding this limitation is crucial for maintaining safety and regulatory compliance in aviation operations. The limit serves to prevent pilot fatigue and ensure that crews are adequately rested and fit to perform their duties, thereby sustaining a high level of operational safety. This regulation reflects industry best practices in managing workload and ensuring that pilots do not exceed safe operational limits.

In the context of the other options, 600, 400, and 300 hours are not permissible limitations for this specific category of operation under Part 135 regulations. The 500-hour limit has been established to balance operational needs with the health and safety of crew members and passengers.