Which operation is prohibited?

• A. Use of autopilot in cruise flight
• B. Normal takeoff and landing with standard configurations
• C. Extended flight in smooth air without adjusting crew alertness
• D. Intentional spins, stalls, aerobatics, steep dives (not associated with an Emergency Descent), or maneuvers resulting in abrupt accelerations.

Answer: (D)

Deliberate maneuvers outside the normal flight envelope are prohibited to protect the airframe, flight controls, and crew from overstress or loss of situational awareness. Spinning, stalling, aerobatics, steep dives (not part of an Emergency Descent), or any maneuver that produces abrupt accelerations push the airplane beyond its tested limits and can lead to loss of control or system failures. Because of the elevated risk and the need to maintain predictable, recoverable flight, these actions are disallowed.

The other scenarios describe routine or standard operating procedures—autopilot use in cruise, normal takeoff and landing with standard configurations, and extended cruise in smooth air with appropriate crew vigilance—that fall within normal operating limits and are not part of the prohibited category.