What condition must be met for gravity fuel systems regarding fuel flow?

For gravity fuel systems, the requirement that the fuel flow must be at least 150% of the takeoff fuel consumption is critical for ensuring safe and reliable operation. This condition ensures that there is a sufficient fuel supply available throughout all phases of the flight, especially during takeoff and initial climb when the demand for fuel is at its highest.

Having 150% of the takeoff fuel consumption accounted for allows for a cushion that compensates for potential fuel flow interruptions, variations in fuel system performance, or changes in aircraft operations that could affect fuel needs. This parameter not only enhances safety by ensuring that the fuel system can meet expected demands but also provides flexibility for variations in operating conditions, ensuring that the aircraft can operate effectively under a variety of circumstances.

Other conditions, such as equal to or less than the takeoff fuel consumption, would not provide the necessary margin of safety and performance, which is why they do not meet the required standard for gravity fuel systems.