Definition
A path and terminator leg used in RNAV/FMS coding to define a procedure turn. The aircraft flies outbound from a fix on a specified course, then executes a 45-degree turn followed by a 180-degree turn in the opposite direction to reverse course and return to the inbound track. The leg terminates when the aircraft intercepts the inbound course back to the fix.
Plain English
It is the database code that tells the flight management system to fly a standard procedure turn — fly outbound, turn 45 degrees one way, then 180 degrees the other way, and roll out heading back toward the fix.
Context Anchor
Seen in instrument procedure coding, RNAV procedure design, and flight management system leg displays when a published procedure turn or course reversal is part of the route.
Derivation
The two-letter code 'PI' comes from ARINC 424, the industry standard that assigns each leg type a unique two-character identifier. Knowing this helps explain why the abbreviation does not match the spelled-out name.
Why Pilots Care
Provides a published method to reverse direction and establish the aircraft on the final approach course without ATC assistance.
Grounding Statement
A PI leg is the published turn-around portion of an instrument route, coded so the navigation system can guide the aircraft through it.
Intuition Check
A PI leg is not just any turn in the procedure. It specifically means a coded course reversal used to turn the aircraft around and align it for the next inbound path.
Example Sentence 1
After crossing the initial approach fix, the FMS sequenced the PI leg and the autopilot began the outbound 45-degree turn.
Example Sentence 2
After completing the PI leg the aircraft intercepted the inbound course and continued on the final approach segment.