Definition
The set of TERPS (Terminal Instrument Procedures) standards that establish the minimum vertical clearance an aircraft must have above terrain and obstacles while flying along an en route segment of an IFR route or feeder route. Standard en route criteria require 1,000 feet of obstacle clearance within the protected airspace of the route (2,000 feet in designated mountainous areas), and these criteria are used when designing published altitudes such as MEA, MOCA, and feeder route altitudes.
Plain English
The rules that decide how much room must be left between an aircraft and the ground or obstacles when flying the en route portion of an instrument route. Normally that buffer is 1,000 feet, or 2,000 feet over mountains.
Context Anchor
Seen when studying feeder routes and how published instrument routes connect the en route structure to the beginning of an instrument approach.
Derivation
En route comes from French and means “on the way.” Obstacle means something that stands in the way, and criteria means standards used to judge or design something. Together, the phrase means the standards used to keep an aircraft safely above obstacles while it is still on the way to the approach.
Why Pilots Care
Directly determines the lowest safe altitude a pilot can accept on an airway or feeder route and is therefore a key factor in both route planning and terrain-avoidance decisions.
Grounding Statement
On a feeder route, the published altitude is not just a suggestion; it is part of the design that keeps the aircraft above known terrain and obstacles along that route.
Intuition Check
Do not read “clearance” here as an air traffic control clearance. In this phrase, obstacle clearance means designed vertical space between the aircraft’s route altitude and obstacles below.
Example Sentence 1
The feeder route altitude was set using en route obstacle clearance criteria, giving us 1,000 feet of guaranteed terrain clearance until reaching the IAF.
Example Sentence 2
Before accepting a direct routing, the controller confirmed that the altitude complied with en route obstacle clearance criteria.