IFR Course Requirements

FAR 91.181 — IFR Course Requirements

FAR 91.181 explains the course IFR pilots must fly in controlled airspace—airway centerlines, direct courses, and allowed maneuvering to clear traffic.

In Plain English

FAR 91.181 sets the basic rule for what course you must fly when operating IFR in controlled airspace. Unless ATC authorizes otherwise, you have to stay on a defined track:

On an ATS route (airway): fly along the centerline of that airway.
On any other route: fly the direct course between the navaids or fixes that define the route.

Why it matters: ATC separates IFR traffic based on the assumption you're tracking exactly where you said you would. Drifting off the centerline or wandering between fixes can erode separation from other aircraft, terrain, and obstacles.

The rule does build in some practical flexibility. You're allowed to maneuver to pass well clear of other air traffic, and in VFR conditions you may maneuver to clear the intended flight path before and during a climb or descent. Outside of those exceptions, if you need to deviate—for weather, for example—you must request and receive an ATC clearance first.

Regulation Text

14 CFR § 91.181

§ 91.181 Course to be flown. Unless otherwise authorized by ATC, no person may operate an aircraft within controlled airspace under IFR except as follows: (a) On an ATS route, along the centerline of that airway. (b) On any other route, along the direct course between the navigational aids or fixes defining that route. However, this section does not prohibit maneuvering the aircraft to pass well clear of other air traffic or the maneuvering of the aircraft in VFR conditions to clear the intended flight path both before and during climb or descent. [Docket 18334, 54 FR 34294, Aug. 18, 1989, as amended by Amdt. 91-296, 72 FR 31679, June 7, 2007]

Oral Exam Questions a DPE Might Ask

Q1When operating IFR in controlled airspace, what course are you required to fly?

Per FAR 91.181, unless ATC authorizes otherwise, you must fly along the centerline of the airway when on an ATS route, or along the direct course between the navaids or fixes defining the route on any other route.

Q2Are you ever allowed to deviate from the assigned course under FAR 91.181?

Yes. FAR 91.181 permits maneuvering to pass well clear of other air traffic, and in VFR conditions you may maneuver to clear your intended flight path before and during climb or descent. Any other deviation requires ATC authorization.

Q3If you need to deviate around a thunderstorm while on an airway, what must you do?

Under FAR 91.181 you must remain on the airway centerline unless otherwise authorized by ATC, so you'd need to request and receive a deviation clearance from ATC before leaving course.

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Related Sections in Part 91

§ 91.1

Part 91 Applicability