Chapter 3 — En Route Operations

En Route Navigation   3-1
Air Route Traffic Control Centers   3-1
Preferred IFR Routes   3-3
Substitute En Route Flight Procedures   3-3
Tower En Route Control   3-4
Airway and Route System   3-4
Monitoring of Navigation Facilities   3-4
LF Airways/Routes   3-4
VHF Airways/Routes   3-6
VHF En Route Obstacle Clearance Areas   3-6
Primary Area   3-6
Secondary Area   3-8
NAVAID Service Volume   3-9
Navigational Gaps   3-10
Changeover Points   3-11
IFR En Route Altitudes   3-12
Minimum En Route Altitude   3-13
Minimum Obstruction Clearance Altitude   3-13
Minimum Vectoring Altitudes   3-13
Minimum Reception Altitude   3-13
Minimum Crossing Altitude   3-13
Maximum Authorized Altitude    3-16
IFR Cruising Altitude or Flight Level   3-16
Lowest Usable Flight Level   3-16
Operations in Other Countries   3-17
Reporting Procedures   3-17
Nonradar Position Reports   3-17
Communication Failure   3-18
Climbing and Descending En Route   3-20
Pilot/Controller Expectations   3-20
Aircraft Speed and Altitude   3-22
Holding Procedures   3-23
ATC Holding Instructions   3-23
Maximum Holding Speed   3-24
High Performance Holding   3-25
Fuel State Awareness   3-25
Diversion Procedures   3-26
En Route RNAV Procedures   3-26
Off Airway Routes   3-26
Direct Flights   3-27
Random RNAV Routes   3-27
Off Route Obstacle Clearance Altitude   3-28
Published RNAV Routes   3-31
Composition of Designators   3-31
Use of Designators in Communications   3-32
RNAV Minimum En Route Altitude   3-33
Minimum IFR Altitude   3-33
WayPoints   3-34
User-Defined Waypoints   3-34
Floating Waypoints   3-34
Computer Navigation Fixes   3-35
High Altitude Airspace Redesign   3-35
Q Routes   3-36
Non-Restrictive Routing   3-36
Navigation Reference System   3-36
T-Routes   3-36
IFR Transition Routes   3-36
Required Navigation Performance   3-37
Reduced Vertical Separation Minimums   3-38