When is a take-off alternate required according to regulations?

A take-off alternate is required when the airport of takeoff has weather conditions that are below the established landing minimums for that airport. This is an essential safety regulation that ensures pilots have a predetermined location to divert to if they cannot land at the intended airport following takeoff due to poor weather conditions.

If the weather at the departure airport does not meet the minimum requirements for a safe landing, having a take-off alternate helps ensure that the aircraft can safely land elsewhere without unnecessarily jeopardizing the flight or passengers.

The other options do not represent the criteria that dictate the need for a take-off alternate in aviation regulations. For instance, merely flying over a certain distance or the number of engines on an aircraft does not inherently necessitate a take-off alternate, nor does the forecast of thunderstorms by itself establish the need for one. The critical factor remains the weather at the airport of takeoff concerning landing minimums.