Under what conditions would a takeoff alternate be required?

A takeoff alternate is required when the weather at the departure airport is below the applicable IFR (Instrument Flight Rules) minimums. This situation ensures that if the flight cannot return to the departure airport shortly after takeoff due to environmental conditions, there is another pre-identified airport nearby that meets the alternate airport criteria and can be safely reached.

Having this operational plan in place is crucial for flight safety, particularly in instances where adverse weather may prevent a safe landing at the departure point. It addresses potential complications such as low visibility or severe weather that could hinder flight operations.

In contrast, while poor visibility or the absence of a control tower may affect flight operations, they do not specifically necessitate a takeoff alternate unless they correspond with not meeting the IFR minimums. Therefore, option C is the only choice that aligns with the regulatory stipulations regarding the requirement for having a takeoff alternate when departing under challenging weather conditions.