Definition
The sequence of fixes, airways, navaids, and procedures that defines an IFR route from departure to destination, written in the standardized text format used in flight plans and ATC clearances (e.g., 'KBOS DCT GDM V3 ALB DCT KSYR').
Plain English
The line of text that spells out, step by step, the path an aircraft will fly between two airports.
Context Anchor
Seen in preferred IFR route listings, flight plan route entries, and ATC clearances.
Derivation
Route comes from an old French word meaning a road or path. String, in this use, means a connected sequence of items or characters. Together, route string means a flight route written as one ordered sequence, not a physical string.
Why Pilots Care
Using the correct route string ensures the filed flight plan matches published preferred routes, reducing the chance of a complex reroute or departure delay.
Intuition Check
Do not read string as a loose or casual description. In this context, a route string is an exact ordered line of route information; changing the order or leaving out an item changes the route.
Example Sentence 1
When filing IFR from Boston to Syracuse, the pilot copied the preferred route string directly from the FAA listing to avoid a reroute.
Example Sentence 2
ATC issued a clearance that matched the route string listed for that altitude and direction of flight.