Off-Airway Route

An off-airway route, also known as an off-route obstruction clearance altitude (OROCA), is a flight path not following a designated airway, providing obstruction clearance with a 1,000-foot buffer in non-mountainous areas and a 2,000-foot buffer in mountainous areas.

Historical Context

Early Aviation

Initially, aviation relied on visual flight rules (VFR) and pilots navigated by landmarks and the sun. As aviation grew, the need for a more structured system for instrument flight rules (IFR) emerged.

Development of Airways

The concept of airways, or designated routes in the sky, emerged as a way to standardize flight paths and improve air traffic control efficiency.

Off-Airway Routes

Off-airway routes, or OROCA, were developed to allow pilots to fly between points that did not lie directly on a designated airway, while still maintaining adequate obstacle clearance.

Modern Usage

Today, off-airway routes are common, particularly for RNAV (Required Navigation Performance) routes, which allow aircraft to fly more direct routes using GPS or other navigation systems, and are published in the Airport/Facility Directory (A/FD).

Obstacle Clearance

The FAA ensures that off-route altitudes provide sufficient obstacle clearance, with the 1,000-foot and 2,000-foot buffers designed to account for terrain and potential obstacles.

Minimum Reception Altitude (MRA)

An MRA is determined by FAA flight inspection traversing an entire route of flight to establish the minimum altitude the navigation signal can be received for the route (which, along with obstacle clearance, defines the Minimum Enroute Altitude - MEA) and for off-course NAVAID facilities that determine a fix.