Definition
A navigation technique used with a Radio Magnetic Indicator (RMI) to estimate the time and distance from the aircraft to a VOR or NDB station. The pilot notes the bearing to the station, turns to place that bearing 90° off the wing (a perpendicular position), and then times how long it takes for the bearing to change by a chosen number of degrees (commonly 10°). Time to the station in minutes equals 60 divided by the degrees of bearing change, multiplied by the minutes elapsed. Distance is then calculated from time and groundspeed.
Plain English
A simple in-flight calculation that lets a pilot work out how far they are from a radio navigation station, and how long it will take to reach it, by flying at right angles to the station and timing how quickly the needle on the cockpit indicator moves through a set number of degrees.
Context Anchor
Seen in navigation planning and in-flight position checks when using radio navigation equipment instead of an automatic distance readout.
Derivation
RMI stands for Radio Magnetic Indicator. The instrument combines a magnetic compass card with a needle that always points to the tuned station, so the pilot can read the bearing to the station directly. The technique itself uses simple geometry: a small angular change observed from a known perpendicular position reveals how far away the station is.
Why Pilots Care
Provides a reliable backup method to estimate arrival time and distance to a station using only bearing information.
Grounding Statement
If the RMI pointer changes direction quickly, the airplane is relatively close to the station; if it changes slowly, the airplane is farther away.
Intuition Check
Do not read “station” here as an airport or a radio broadcast station; it means a selected ground navigation transmitter. Also, the RMI does not measure distance directly—the pilot estimates distance from how fast the pointer changes direction.
Example Sentence 1
Without DME on board, the pilot performed a time and distance check from a station using a RMI to estimate they were about 20 nautical miles from the VOR.
Example Sentence 2
During the approach briefing the crew performed a time and distance check from the station using the RMI to verify their position fix.