Non-Free-Fall Motion and Newton's Second Law of Motion
The image below shows the man at the instant he falls from the airplane. At the instant he leaves the airplane, we know that his mass multiplied by his acceleration is equal to his mass multiplied by the acceleration due to gravity (g).
The green box above says that the man's mass times his acceleration is equal to his mass times the acceleration due to gravity. Notice: The man's mass appears on both sides of the equation.