What should you do if you had a late departure due to weather and are 90 minutes away from your destination with the sun setting?

Flying to your alternate is the most prudent choice in this scenario, particularly when factoring in the setting sun and the potential difficulties associated with flying in reduced visibility due to darkness. As you are 90 minutes out from your destination and the sun is setting, you may encounter visual challenges as light diminishes.

When the light fades, you will have limited visual references that can complicate navigation and landing, especially in an unfamiliar area or if your destination does not have adequate lighting for instrument approaches. Additionally, if you have already experienced delays due to weather, the conditions at your destination could be further impacted, perhaps leading to additional challenges.

By heading to your alternate, you ensure a safer option where you can land in a more stable environment, allowing for a proper assessment of the weather conditions and ensuring that you arrive at an airport that is equipped to handle your arrival safely under IFR conditions. This decision aligns with regulations regarding the need for a workable alternate in the case of changing weather conditions and night operations.