As pilot in command of an aircraft, under which situation can you deviate from an ATC clearance?

• A. In response to a traffic alert and collision avoidance system resolution advisory
• B. When the weather deteriorates
• C. When told by ATC to deviate
• D. When entering a congested airspace

Answer: (A)

You may override an ATC clearance only to avoid an imminent collision, as required by a TCAS resolution advisory. When TCAS issues a RA, you must execute the prescribed maneuver immediately to prevent a collision, even if it means deviating from your current clearance. After the maneuver, you should contact ATC as soon as practicable to re-establish separation and obtain a new clearance.

Weather deterioration, congested airspace, or simply being told by ATC to deviate do not authorize unilateral deviation from an ATC clearance in normal operations. Those situations require following ATC instructions or requesting a revised clearance, not disregarding the existing clearance.