What does an IFR pilot need in order to deviate from their assigned course?

• A. A weather deviation form
• B. A filed alternate route
• C. ATC clearance
• D. A new IFR flight plan

Answer: (C)

In IFR operations, you fly under ATC clearance and are expected to follow the route and altitude assigned by the controller. Any change to your course must have ATC authorization. That means deviations from the assigned path aren’t allowed on your own initiative; you request a deviation or a direct routing, and ATC may approve a different course, direct-to a waypoint, or a rerouted clearance. Without that clearance, you’re still expected to stay on the assigned route.

Other options don’t authorize a mid-flight change. A weather deviation form isn’t a thing you file to permit a turn; a filed alternate route is part of planning for alternate airport considerations, not a mid-flight clearance to deviate; a new IFR flight plan isn’t needed just to change course if ATC issues a revised clearance. In an emergency, you may deviate to handle the immediate danger, but you would still notify ATC as soon as possible.

So, the only thing that permits deviating from the assigned course is ATC clearance.