What was the reason behind frightening of the pilot of Dakota second time?

What was the reason behind frightening of the pilot of Dakota second time?

Answer: While flying through the storm, the pilot of the black aeroplane waved at the narrator to follow his lead. The narrator flew his Dakota plane behind him for half an hour. He found that the fuel in his aeroplane could allow him to fly for five to ten minutes more. Therefore, he got frightened once again.