What is the primary purpose of including an alternate airport in IFR flight planning?

The primary purpose of including an alternate airport in IFR flight planning is to account for potential weather deterioration at the destination. Weather conditions can change unexpectedly, and an alternate airport provides a safe option for landing if the forecasted weather at the intended destination becomes unsuitable for landing upon arrival. This decision emphasizes safety, allowing pilots to avoid situations where they might arrive at an airport that has become unreachable due to poor visibility or other adverse conditions.

Including an alternate also ensures that pilots have a contingency plan if their planned route encounters unforeseen obstacles, such as thunderstorms or low ceilings. The requirement for an alternate airport is an essential aspect of IFR operations, reflecting the need for preparedness in case the destination airport cannot be used for landing due to deteriorating weather conditions.