When an ATC clearance has been obtained, no pilot in command may deviate from that clearance, unless that pilot obtains an amended clearance. The one exception to this regulation is

• A. An emergency
• B. Lost communications
• C. Weather deviation
• D. Pilot request

Answer: (A)

The pilot in command has the authority to deviate from an ATC clearance when doing so is necessary to keep the flight safe. The only general exception to needing an amended clearance is an emergency. In an emergency, you may take whatever action is required immediately to maintain safety—such as altering course, changing altitude, or diverting to a different airport—without waiting for ATC clearance. After the situation is under control, you should inform ATC and obtain the appropriate amended clearance or declare an emergency if needed (squawk 7700). Lost communications and weather-related changes do not provide the same blanket exception; they require following established procedures or obtaining a new clearance, whereas an emergency authorizes immediate deviation to prevent harm.