When must the XFEED selector be set to OFF?

The XFEED (Crossfeed) selector must be set to OFF during takeoff and landing to ensure that fuel from the wing tanks is supplied directly to the engines without any crossfeeding. This configuration is crucial for maintaining optimal engine performance and ensuring fuel system redundancy.

During takeoff and landing, the aircraft is operating in a critical phase where engine reliability is paramount, and the risk of fuel imbalance must be minimized. Setting the XFEED to OFF ensures that each engine is fed exclusively from its respective fuel tank, which helps in managing fuel weight distribution, stabilizing the aircraft’s center of gravity, and enhancing operational safety.

In contrast, the other choices involve phases of flight where crossfeeding may not have the same potential for risk or be necessary for operational flexibility. For example, during taxi or climb, crossfeeding can be allowed if required for fuel management, while approaching the destination could also necessitate normal fuel configurations based on operational needs rather than strict adherence to OFF.