Final answer:
The flight crew requires a performance alternate before departure in situations where standard operations may be compromised, illustrated by the incident of a plane losing power and safely landing at an alternate site.
Step-by-step explanation:
The flight crew must have a performance alternate before departure when there might be circumstances that compromise the standard operation of the aircraft, such as technical issues, fuel shortages, or unexpected weather conditions. For example, in the case of the 767 flight from Montreal that faced a fuel issue and power loss, having an alternate plan was crucial to ensure a safe landing. The pilots used their skills and knowledge to divert to an old RAF base, demonstrating the importance of having a performance alternate to manage unexpected situations.
The overall process of airline travel, including the checks and bottlenecks such as baggage check, security screening, and boarding, is an analogy for understanding the importance of preparation and procedural bottlenecks. It highlights why each step, such as establishing a performance alternate, is critical for the safe operation of a flight.