Flight instructors should always guard the controls and be prepared to take control of the aircraft. When necessary, the instructor  should take the controls and calmly announce, “I have the flight controls.” If an instructor allows a learner to remain on the controls,  the instructor may not have full and effective control of the aircraft. Anxious learners can be incredibly strong and usually exhibit  reactions inappropriate to the situation. If a recovery is necessary, there is absolutely nothing to be gained by having the learner on the  controls and having to fight for control of the aircraft. Learners should never be allowed to exceed the flight instructor’s limits. Flight  instructors should not exceed their own ability to perceive a problem, decide upon a course of action, and physically react within their  ability to fly the aircraft.  Commonly known as the “sterile flight deck rule,” Title 14 of the Code of Federal Regulations (14 CFR)  part 121,  section  121.542 requires airline flight crewmembers to refrain from nonessential activities during critical phases of flight. As defined in the  regulation, critical phases of flight are all ground operations involving taxi, takeoff, and landing, and all other flight operations below  10,000 feet except cruise flight. Nonessential activities include such activities as eating, reading a newspaper, or chatting. A series of  aircraft accidents caused by flight crews who were distracted from their flight duties during critical phases of the flight caused the  FAA to propose the rule. While the regulation grew out of accidents in the airline industry, it holds true for the entire aviation  community. Pilots can improve flight safety significantly by reducing distractions during critical phases of flight. It is important the  flight instructor not only teach the concept of a sterile  flight deck  but also model such behavior during flight instruction.  Sterile Flight Deck Rule  Use of Distractions  National Transportation Safety Board (NTSB) statistics reveal that most stall/spin accidents occurred when the pilot’s attention was  diverted from the primary task of flying the aircraft. Sixty percent of stall/spin accidents occurred during takeoff and landing, and  twenty percent were preceded by engine failure. Preoccupation inside or outside the flight deck while changing aircraft configuration  or trim, maneuvering to avoid other traffic, or clearing hazardous obstacles during takeoff and climb could create a potential stall/spin  situation. The intentional practice of stalls and spins seldom resulted in an accident. The real danger was inadvertent stalls induced by  distractions during routine flight situations.  9-9 Figure 9-8.  During this procedure, a visual check is recommended to see that the other person actually has the flight controls. When  returning the controls to the instructor, the learner should follow the same procedure the instructor used when giving control to the  learner. The learner should stay on the controls and keep flying the aircraft until the instructor says, “I have the flight controls.”  There should never be any doubt about who is flying the aircraft. 