How much fuel must a pilot plan to carry if they need to designate an alternate airport on their IFR flight plan?

When planning for an IFR flight that designates an alternate airport, the pilot must ensure they have sufficient fuel reserves to safely accommodate the possibility of diverting to that alternate. The requirement is to have enough fuel to reach the intended destination, then an additional reserve amount. According to regulations, this reserve is specifically defined as the fuel needed to fly for at least 45 minutes at normal cruising speed.

Carrying fuel sufficient for 45 minutes of flight time beyond the arrival at the intended destination allows for potential delays or increased fuel consumption during the approach and landing at the alternate airport. This is important for maintaining safety in unpredictable situations, ensuring that pilots can react to changing conditions without the immediate concern of fuel shortage.

The other choices, which suggest different time amounts, do not align with the standard requirements established for IFR operations involving alternate airports. Hence, the designation of having enough fuel to arrive at the destination, plus an additional 45 minutes of flight, is the correct planning strategy for these scenarios.