Definition
The set of regulatory rules a pilot must follow when two-way radio contact with air traffic control is lost during IFR flight. Under 14 CFR 91.185, the pilot continues the flight using prescribed defaults for route, altitude, and timing: fly the route assigned in the last ATC clearance (or, if none, the route ATC told you to expect, or the route filed); fly the highest of the assigned, expected, or minimum IFR altitude for each segment; and depart the clearance limit at the expected further clearance time or, if none was given, on the flight plan estimated time of arrival.
Plain English
What you do if your radios stop working while flying on instruments. The rules tell you which route to fly, what altitude to hold, and when to begin your approach, so ATC can predict where you will be even though they cannot talk to you.
Context Anchor
Seen in instrument departure instructions, especially in notes for Standard Instrument Departures, and used when radio contact with air traffic control is lost after takeoff or during instrument flight.
Why Pilots Care
Prevents conflicts with other traffic and lets the flight continue without ATC guidance.
Analogy
It is like agreeing on a meeting place before a phone battery dies. If you cannot talk anymore, everyone still knows the plan.
Intuition Check
Do not read “lost communication” as only a totally dead radio. It also includes situations where reliable two-way contact with air traffic control cannot be maintained.
Example Sentence 1
After the radios went silent, the pilot followed lost communication procedures and continued on the last assigned route at the highest applicable altitude.
Example Sentence 2
Lost communication procedures guided the aircraft to climb to the published altitude and proceed to the destination airport.